Eval

Nvim :help pages, generated from source using the tree-sitter-vimdoc parser.

Expression evaluation expression expr E15 eval

Using expressions is introduced in chapter 41 of the user manual usr_41.txt.

1. Variables variables

1.1 Variable types

E712 E896 E897 E899 There are seven types of variables:

Number Integer Number A 32 or 64 bit signed number. expr-number The number of bits is available in v:numbersize. Examples: -123 0x10 0177 0o177 0b1011

Float A floating point number. floating-point-format Float Examples: 123.456 1.15e-6 -1.1e3

String A NUL terminated string of 8-bit unsigned characters (bytes). expr-string Examples: "ab\txx\"--" 'x-z''a,c'

Funcref A reference to a function Funcref. Example: function("strlen") It can be bound to a dictionary and arguments, it then works like a Partial. Example: function("Callback", [arg], myDict)

List An ordered sequence of items, see List for details. Example: [1, 2, ['a', 'b']]

Dictionary An associative, unordered array: Each entry has a key and a value. Dictionary Examples:

{"blue": "#0000ff", "red": "#ff0000"}
#{blue: "#0000ff", red: "#ff0000"}

Blob Binary Large Object. Stores any sequence of bytes. See Blob for details. Example: 0zFF00ED015DAF 0z is an empty Blob.

The Number and String types are converted automatically, depending on how they are used.

Conversion from a Number to a String is by making the ASCII representation of the Number. Examples:

Number 123 --> String "123"

Number 0 --> String "0"

Number -1 --> String "-1"

octal
Conversion from a String to a Number is done by converting the first digits to a number. Hexadecimal "0xf9", Octal "017" or "0o17", and Binary "0b10" numbers are recognized. If the String doesn't start with digits, the result is zero. Examples:

String "456" --> Number 456

String "6bar" --> Number 6

String "foo" --> Number 0

String "0xf1" --> Number 241

String "0100" --> Number 64

String "0o100" --> Number 64

String "0b101" --> Number 5

String "-8" --> Number -8

String "+8" --> Number 0

To force conversion from String to Number, add zero to it:

:echo "0100" + 0

To avoid a leading zero to cause octal conversion, or for using a different base, use str2nr().

TRUE FALSE Boolean For boolean operators Numbers are used. Zero is FALSE, non-zero is TRUE. You can also use v:false and v:true. When TRUE is returned from a function it is the Number one, FALSE is the number zero.

Note that in the command:

:if "foo"
:" NOT executed

"foo" is converted to 0, which means FALSE. If the string starts with a non-zero number it means TRUE:

:if "8foo"
:" executed

To test for a non-empty string, use empty():

:if !empty("foo")

falsy truthy An expression can be used as a condition, ignoring the type and only using whether the value is "sort of true" or "sort of false". Falsy is: the number zero empty string, blob, list or dictionary Other values are truthy. Examples: 0 falsy 1 truthy -1 truthy 0.0 falsy 0.1 truthy '' falsy 'x' truthy [] falsy [0] truthy {} falsy #{x: 1} truthy 0z falsy 0z00 truthy

non-zero-arg
Function arguments often behave slightly different from TRUE: If the argument is present and it evaluates to a non-zero Number, v:true or a non-empty String, then the value is considered to be TRUE. Note that " " and "0" are also non-empty strings, thus considered to be TRUE. A List, Dictionary or Float is not a Number or String, thus evaluate to FALSE.

E745 E728 E703 E729 E730 E731 E974 E975 E976 List, Dictionary, Funcref, and Blob types are not automatically converted.

E805 E806 E808 When mixing Number and Float the Number is converted to Float. Otherwise there is no automatic conversion of Float. You can use str2float() for String to Float, printf() for Float to String and float2nr() for Float to Number.

E362 E891 E892 E893 E894 E907 When expecting a Float a Number can also be used, but nothing else.

no-type-checking
You will not get an error if you try to change the type of a variable.

1.2 Function references

Funcref E695 E718 E1192 A Funcref variable is obtained with the function() function, the funcref() function or created with the lambda expression expr-lambda. It can be used in an expression in the place of a function name, before the parenthesis around the arguments, to invoke the function it refers to. Example:

:let Fn = function("MyFunc")
:echo Fn()

E704 E705 E707 A Funcref variable must start with a capital, "s:", "w:", "t:" or "b:". You can use "g:" but the following name must still start with a capital. You cannot have both a Funcref variable and a function with the same name.

A special case is defining a function and directly assigning its Funcref to a Dictionary entry. Example:

:function dict.init() dict
:   let self.val = 0
:endfunction

The key of the Dictionary can start with a lower case letter. The actual function name is not used here. Also see numbered-function.

A Funcref can also be used with the :call command:

:call Fn()
:call dict.init()

The name of the referenced function can be obtained with string().

:let func = string(Fn)

You can use call() to invoke a Funcref and use a list variable for the arguments:

:let r = call(Fn, mylist)

Partial
A Funcref optionally binds a Dictionary and/or arguments. This is also called a Partial. This is created by passing the Dictionary and/or arguments to function() or funcref(). When calling the function the Dictionary and/or arguments will be passed to the function. Example:

let Cb = function('Callback', ['foo'], myDict)
call Cb('bar')

This will invoke the function as if using:

call myDict.Callback('foo', 'bar')

Note that binding a function to a Dictionary also happens when the function is a member of the Dictionary:

let myDict.myFunction = MyFunction
call myDict.myFunction()

Here MyFunction() will get myDict passed as "self". This happens when the "myFunction" member is accessed. When assigning "myFunction" to otherDict and calling it, it will be bound to otherDict:

let otherDict.myFunction = myDict.myFunction
call otherDict.myFunction()

Now "self" will be "otherDict". But when the dictionary was bound explicitly this won't happen:

let myDict.myFunction = function(MyFunction, myDict)
let otherDict.myFunction = myDict.myFunction
call otherDict.myFunction()

Here "self" will be "myDict", because it was bound explicitly.

1.3 Lists

list List Lists E686 A List is an ordered sequence of items. An item can be of any type. Items can be accessed by their index number. Items can be added and removed at any position in the sequence.

List creation

E696 E697 A List is created with a comma-separated list of items in square brackets. Examples:

:let mylist = [1, two, 3, "four"]
:let emptylist = []

An item can be any expression. Using a List for an item creates a List of Lists:

:let nestlist = [[11, 12], [21, 22], [31, 32]]

An extra comma after the last item is ignored.

List index

list-index E684 An item in the List can be accessed by putting the index in square brackets after the List. Indexes are zero-based, thus the first item has index zero.

:let item = mylist[0]		" get the first item: 1
:let item = mylist[2]		" get the third item: 3

When the resulting item is a list this can be repeated:

:let item = nestlist[0][1]	" get the first list, second item: 12

A negative index is counted from the end. Index -1 refers to the last item in the List, -2 to the last but one item, etc.

:let last = mylist[-1]		" get the last item: "four"

To avoid an error for an invalid index use the get() function. When an item is not available it returns zero or the default value you specify:

:echo get(mylist, idx)
:echo get(mylist, idx, "NONE")

List concatenation

list-concatenation
Two lists can be concatenated with the "+" operator:

:let longlist = mylist + [5, 6]
:let longlist = [5, 6] + mylist

To prepend or append an item, turn it into a list by putting [] around it.

A list can be concatenated with another one in-place using :let+= or extend():

:let mylist += [7, 8]
:call extend(mylist, [7, 8])

See list-modification below for more about changing a list in-place.

Sublist

sublist
A part of the List can be obtained by specifying the first and last index, separated by a colon in square brackets:

:let shortlist = mylist[2:-1]	" get List [3, "four"]

Omitting the first index is similar to zero. Omitting the last index is similar to -1.

:let endlist = mylist[2:]	" from item 2 to the end: [3, "four"]
:let shortlist = mylist[2:2]	" List with one item: [3]
:let otherlist = mylist[:]	" make a copy of the List

Notice that the last index is inclusive. If you prefer using an exclusive index use the slice() method.

If the first index is beyond the last item of the List or the second item is before the first item, the result is an empty list. There is no error message.

If the second index is equal to or greater than the length of the list the length minus one is used:

:let mylist = [0, 1, 2, 3]
:echo mylist[2:8]		" result: [2, 3]

NOTE: mylist[s:e] means using the variable "s:e" as index. Watch out for using a single letter variable before the ":". Insert a space when needed: mylist[s : e].

List identity

list-identity
When variable "aa" is a list and you assign it to another variable "bb", both variables refer to the same list. Thus changing the list "aa" will also change "bb":

:let aa = [1, 2, 3]
:let bb = aa
:call add(aa, 4)
:echo bb

[1, 2, 3, 4]

Making a copy of a list is done with the copy() function. Using [:] also works, as explained above. This creates a shallow copy of the list: Changing a list item in the list will also change the item in the copied list:

:let aa = [[1, 'a'], 2, 3]
:let bb = copy(aa)
:call add(aa, 4)
:let aa[0][1] = 'aaa'
:echo aa

[[1, aaa], 2, 3, 4]

:echo bb

[[1, aaa], 2, 3]

To make a completely independent list use deepcopy(). This also makes a copy of the values in the list, recursively. Up to a hundred levels deep.

The operator "is" can be used to check if two variables refer to the same List. "isnot" does the opposite. In contrast "==" compares if two lists have the same value.

:let alist = [1, 2, 3]
:let blist = [1, 2, 3]
:echo alist is blist

:echo alist == blist

Note about comparing lists: Two lists are considered equal if they have the same length and all items compare equal, as with using "==". There is one exception: When comparing a number with a string they are considered different. There is no automatic type conversion, as with using "==" on variables. Example:

echo 4 == "4"

echo [4] == ["4"]

Thus comparing Lists is more strict than comparing numbers and strings. You can compare simple values this way too by putting them in a list:

:let a = 5
:let b = "5"
:echo a == b

:echo [a] == [b]

List unpack

To unpack the items in a list to individual variables, put the variables in square brackets, like list items:

:let [var1, var2] = mylist

When the number of variables does not match the number of items in the list this produces an error. To handle any extra items from the list append ";" and a variable name:

:let [var1, var2; rest] = mylist

This works like:

:let var1 = mylist[0]
:let var2 = mylist[1]
:let rest = mylist[2:]

Except that there is no error if there are only two items. "rest" will be an empty list then.

List modification

list-modification
To change a specific item of a list use :let this way:

:let list[4] = "four"
:let listlist[0][3] = item

To change part of a list you can specify the first and last item to be modified. The value must at least have the number of items in the range:

:let list[3:5] = [3, 4, 5]

To add items to a List in-place, you can use :let+= (list-concatenation):

:let listA = [1, 2]
:let listA += [3, 4]

When two variables refer to the same List, changing one List in-place will cause the referenced List to be changed in-place:

:let listA = [1, 2]
:let listB = listA
:let listB += [3, 4]
:echo listA
[1, 2, 3, 4]

Adding and removing items from a list is done with functions. Here are a few examples:

:call insert(list, 'a')		" prepend item 'a'
:call insert(list, 'a', 3)	" insert item 'a' before list[3]
:call add(list, "new")		" append String item
:call add(list, [1, 2])		" append a List as one new item
:call extend(list, [1, 2])	" extend the list with two more items
:let i = remove(list, 3)	" remove item 3
:unlet list[3]			" idem
:let l = remove(list, 3, -1)	" remove items 3 to last item
:unlet list[3 : ]		" idem
:call filter(list, 'v:val !~ "x"')  " remove items with an 'x'

Changing the order of items in a list:

:call sort(list)		" sort a list alphabetically
:call reverse(list)		" reverse the order of items
:call uniq(sort(list))		" sort and remove duplicates

For loop

The :for loop executes commands for each item in a List, String or Blob. A variable is set to each item in sequence. Example with a List:

:for item in mylist
:   call Doit(item)
:endfor

This works like:

:let index = 0
:while index < len(mylist)
:   let item = mylist[index]
:   :call Doit(item)
:   let index = index + 1
:endwhile

If all you want to do is modify each item in the list then the map() function will be a simpler method than a for loop.

Just like the :let command, :for also accepts a list of variables. This requires the argument to be a List of Lists.

:for [lnum, col] in [[1, 3], [2, 8], [3, 0]]
:   call Doit(lnum, col)
:endfor

This works like a :let command is done for each list item. Again, the types must remain the same to avoid an error.

It is also possible to put remaining items in a List variable:

:for [i, j; rest] in listlist
:   call Doit(i, j)
:   if !empty(rest)
:      echo "remainder: " .. string(rest)
:   endif
:endfor

For a Blob one byte at a time is used.

For a String one character, including any composing characters, is used as a String. Example:

for c in text
  echo 'This character is ' .. c
endfor

List functions

E714
Functions that are useful with a List:

:let r = call(funcname, list)	" call a function with an argument list
:if empty(list)			" check if list is empty
:let l = len(list)		" number of items in list
:let big = max(list)		" maximum value in list
:let small = min(list)		" minimum value in list
:let xs = count(list, 'x')	" count nr of times 'x' appears in list
:let i = index(list, 'x')	" index of first 'x' in list
:let lines = getline(1, 10)	" get ten text lines from buffer
:call append('$', lines)	" append text lines in buffer
:let list = split("a b c")	" create list from items in a string
:let string = join(list, ', ')	" create string from list items
:let s = string(list)		" String representation of list
:call map(list, '">> " .. v:val')  " prepend ">> " to each item

Don't forget that a combination of features can make things simple. For example, to add up all the numbers in a list:

:exe 'let sum = ' .. join(nrlist, '+')

1.4 Dictionaries

Dict dict Dictionaries Dictionary A Dictionary is an associative array: Each entry has a key and a value. The entry can be located with the key. The entries are stored without a specific ordering.

Dictionary creation

E720 E721 E722 E723 A Dictionary is created with a comma-separated list of entries in curly braces. Each entry has a key and a value, separated by a colon. Each key can only appear once. Examples:

:let mydict = {1: 'one', 2: 'two', 3: 'three'}
:let emptydict = {}

E713 E716 E717 A key is always a String. You can use a Number, it will be converted to a String automatically. Thus the String '4' and the number 4 will find the same entry. Note that the String '04' and the Number 04 are different, since the Number will be converted to the String '4', leading zeros are dropped. The empty string can also be used as a key. literal-Dict #{} To avoid having to put quotes around every key the #{} form can be used. This does require the key to consist only of ASCII letters, digits, '-' and '_'. Example:

:let mydict = #{zero: 0, one_key: 1, two-key: 2, 333: 3}

Note that 333 here is the string "333". Empty keys are not possible with #{}.

A value can be any expression. Using a Dictionary for a value creates a nested Dictionary:

:let nestdict = {1: {11: 'a', 12: 'b'}, 2: {21: 'c'}}

An extra comma after the last entry is ignored.

Accessing entries

The normal way to access an entry is by putting the key in square brackets:

:let val = mydict["one"]
:let mydict["four"] = 4

You can add new entries to an existing Dictionary this way, unlike Lists.

For keys that consist entirely of letters, digits and underscore the following form can be used expr-entry:

:let val = mydict.one
:let mydict.four = 4

Since an entry can be any type, also a List and a Dictionary, the indexing and key lookup can be repeated:

:echo dict.key[idx].key

Dictionary to List conversion

You may want to loop over the entries in a dictionary. For this you need to turn the Dictionary into a List and pass it to :for.

Most often you want to loop over the keys, using the keys() function:

:for key in keys(mydict)
:   echo key .. ': ' .. mydict[key]
:endfor

The List of keys is unsorted. You may want to sort them first:

:for key in sort(keys(mydict))

To loop over the values use the values() function:

:for v in values(mydict)
:   echo "value: " .. v
:endfor

If you want both the key and the value use the items() function. It returns a List in which each item is a List with two items, the key and the value:

:for [key, value] in items(mydict)
:   echo key .. ': ' .. value
:endfor

Dictionary identity

dict-identity
Just like Lists you need to use copy() and deepcopy() to make a copy of a Dictionary. Otherwise, assignment results in referring to the same Dictionary:

:let onedict = {'a': 1, 'b': 2}
:let adict = onedict
:let adict['a'] = 11
:echo onedict['a']
11

Two Dictionaries compare equal if all the key-value pairs compare equal. For more info see list-identity.

Dictionary modification

dict-modification
To change an already existing entry of a Dictionary, or to add a new entry, use :let this way:

:let dict[4] = "four"
:let dict['one'] = item

Removing an entry from a Dictionary is done with remove() or :unlet. Three ways to remove the entry with key "aaa" from dict:

:let i = remove(dict, 'aaa')
:unlet dict.aaa
:unlet dict['aaa']

Merging a Dictionary with another is done with extend():

:call extend(adict, bdict)

This extends adict with all entries from bdict. Duplicate keys cause entries in adict to be overwritten. An optional third argument can change this. Note that the order of entries in a Dictionary is irrelevant, thus don't expect ":echo adict" to show the items from bdict after the older entries in adict.

Weeding out entries from a Dictionary can be done with filter():

:call filter(dict, 'v:val =~ "x"')

This removes all entries from "dict" with a value not matching 'x'. This can also be used to remove all entries:

call filter(dict, 0)

Dictionary function

Dictionary-function self E725 E862 When a function is defined with the "dict" attribute it can be used in a special way with a dictionary. Example:

:function Mylen() dict
:   return len(self.data)
:endfunction
:let mydict = {'data': [0, 1, 2, 3], 'len': function("Mylen")}
:echo mydict.len()

This is like a method in object oriented programming. The entry in the Dictionary is a Funcref. The local variable "self" refers to the dictionary the function was invoked from.

It is also possible to add a function without the "dict" attribute as a Funcref to a Dictionary, but the "self" variable is not available then.

numbered-function anonymous-function To avoid the extra name for the function it can be defined and directly assigned to a Dictionary in this way:

:let mydict = {'data': [0, 1, 2, 3]}
:function mydict.len()
:   return len(self.data)
:endfunction
:echo mydict.len()

The function will then get a number and the value of dict.len is a Funcref that references this function. The function can only be used through a Funcref. It will automatically be deleted when there is no Funcref remaining that refers to it.

It is not necessary to use the "dict" attribute for a numbered function.

If you get an error for a numbered function, you can find out what it is with a trick. Assuming the function is 42, the command is:

:function g:42

Functions for Dictionaries

E715
Functions that can be used with a Dictionary:

:if has_key(dict, 'foo')	" TRUE if dict has entry with key "foo"
:if empty(dict)			" TRUE if dict is empty
:let l = len(dict)		" number of items in dict
:let big = max(dict)		" maximum value in dict
:let small = min(dict)		" minimum value in dict
:let xs = count(dict, 'x')	" count nr of times 'x' appears in dict
:let s = string(dict)		" String representation of dict
:call map(dict, '">> " .. v:val')  " prepend ">> " to each item

1.5 Blobs

blob Blob Blobs E978 A Blob is a binary object. It can be used to read an image from a file and send it over a channel, for example.

A Blob mostly behaves like a List of numbers, where each number has the value of an 8-bit byte, from 0 to 255.

Blob creation

A Blob can be created with a blob-literal:

:let b = 0zFF00ED015DAF

Dots can be inserted between bytes (pair of hex characters) for readability, they don't change the value:

:let b = 0zFF00.ED01.5DAF

A blob can be read from a file with readfile() passing the {type} argument set to "B", for example:

:let b = readfile('image.png', 'B')

Blob index

blob-index E979 A byte in the Blob can be accessed by putting the index in square brackets after the Blob. Indexes are zero-based, thus the first byte has index zero.

:let myblob = 0z00112233
:let byte = myblob[0]		" get the first byte: 0x00
:let byte = myblob[2]		" get the third byte: 0x22

A negative index is counted from the end. Index -1 refers to the last byte in the Blob, -2 to the last but one byte, etc.

:let last = myblob[-1]		" get the last byte: 0x33

To avoid an error for an invalid index use the get() function. When an item is not available it returns -1 or the default value you specify:

:echo get(myblob, idx)
:echo get(myblob, idx, 999)

Blob iteration

The :for loop executes commands for each byte of a Blob. The loop variable is set to each byte in the Blob. Example:

:for byte in 0z112233
:   call Doit(byte)
:endfor

This calls Doit() with 0x11, 0x22 and 0x33.

Blob concatenation

blob-concatenation
Two blobs can be concatenated with the "+" operator:

:let longblob = myblob + 0z4455
:let longblob = 0z4455 + myblob

A blob can be concatenated with another one in-place using :let+=:

:let myblob += 0z6677

See blob-modification below for more about changing a blob in-place.

Part of a blob

A part of the Blob can be obtained by specifying the first and last index, separated by a colon in square brackets:

:let myblob = 0z00112233
:let shortblob = myblob[1:2]	" get 0z1122
:let shortblob = myblob[2:-1]	" get 0z2233

Omitting the first index is similar to zero. Omitting the last index is similar to -1.

:let endblob = myblob[2:]	" from item 2 to the end: 0z2233
:let shortblob = myblob[2:2]	" Blob with one byte: 0z22
:let otherblob = myblob[:]	" make a copy of the Blob

If the first index is beyond the last byte of the Blob or the second index is before the first index, the result is an empty Blob. There is no error message.

If the second index is equal to or greater than the length of the Blob the length minus one is used:

:echo myblob[2:8]		" result: 0z2233

Blob modification

blob-modification
To change a specific byte of a blob use :let this way:

:let blob[4] = 0x44

When the index is just one beyond the end of the Blob, it is appended. Any higher index is an error.

To change a sequence of bytes the [:] notation can be used:

let blob[1:3] = 0z445566

The length of the replaced bytes must be exactly the same as the value provided. E972

To change part of a blob you can specify the first and last byte to be modified. The value must have the same number of bytes in the range:

:let blob[3:5] = 0z334455

To add items to a Blob in-place, you can use :let+= (blob-concatenation):

:let blobA = 0z1122
:let blobA += 0z3344

When two variables refer to the same Blob, changing one Blob in-place will cause the referenced Blob to be changed in-place:

:let blobA = 0z1122
:let blobB = blobA
:let blobB += 0z3344
:echo blobA
0z11223344

You can also use the functions add(), remove() and insert().

Blob identity

Blobs can be compared for equality:

if blob == 0z001122

And for equal identity:

if blob is otherblob

blob-identity E977 When variable "aa" is a Blob and you assign it to another variable "bb", both variables refer to the same Blob. Then the "is" operator returns true.

When making a copy using [:] or copy() the values are the same, but the identity is different:

:let blob = 0z112233
:let blob2 = blob
:echo blob == blob2

:echo blob is blob2

:let blob3 = blob[:]
:echo blob == blob3

:echo blob is blob3

Making a copy of a Blob is done with the copy() function. Using [:] also works, as explained above.

1.6 More about variables

more-variables
If you need to know the type of a variable or expression, use the type() function.

When the '!' flag is included in the 'shada' option, global variables that start with an uppercase letter, and don't contain a lowercase letter, are stored in the shada file shada-file.

When the 'sessionoptions' option contains "global", global variables that start with an uppercase letter and contain at least one lowercase letter are stored in the session file session-file.

variable name can be stored where

my_var_6 not My_Var_6 session file MY_VAR_6 shada file

It's possible to form a variable name with curly braces, see curly-braces-names.

2. Expression syntax expression-syntax

Expression syntax summary, from least to most significant:

expr1 expr2 expr2 ? expr1 : expr1 if-then-else

expr2 expr3 expr3 || expr3 ... logical OR

expr3 expr4 expr4 && expr4 ... logical AND

expr4 expr5 expr5 == expr5 equal expr5 != expr5 not equal expr5 > expr5 greater than expr5 >= expr5 greater than or equal expr5 < expr5 smaller than expr5 <= expr5 smaller than or equal expr5 =~ expr5 regexp matches expr5 !~ expr5 regexp doesn't match

expr5 ==? expr5 equal, ignoring case expr5 ==# expr5 equal, match case etc. As above, append ? for ignoring case, # for matching case

expr5 is expr5 same List, Dictionary or Blob instance expr5 isnot expr5 different List, Dictionary or Blob instance

expr5 expr6 expr6 + expr6 ... number addition, list or blob concatenation expr6 - expr6 ... number subtraction expr6 . expr6 ... string concatenation expr6 .. expr6 ... string concatenation

expr6 expr7 expr7 * expr7 ... number multiplication expr7 / expr7 ... number division expr7 % expr7 ... number modulo

expr7 expr8 ! expr7 logical NOT

expr7 unary minus + expr7 unary plus

expr8 expr9 expr8[expr1] byte of a String or item of a List expr8[expr1 : expr1] substring of a String or sublist of a List expr8.name entry in a Dictionary expr8(expr1, ...) function call with Funcref variable expr8->name(expr1, ...) method call

expr9 number number constant "string" string constant, backslash is special 'string' string constant, ' is doubled [expr1, ...] List {expr1: expr1, ...} Dictionary #{key: expr1, ...} Dictionary &option option value (expr1) nested expression variable internal variable va{ria}ble internal variable with curly braces $VAR environment variable @r contents of register "r" function(expr1, ...) function call func{ti}on(expr1, ...) function call with curly braces {args -> expr1} lambda expression

"..." indicates that the operations in this level can be concatenated. Example:

&nu || &list && &shell == "csh"

All expressions within one level are parsed from left to right.

Expression nesting is limited to 1000 levels deep (300 when build with MSVC) to avoid running out of stack and crashing. E1169

expr1 expr1 ternary falsy-operator ?? E109

The ternary operator: expr2 ? expr1 : expr1 The falsy operator: expr2 ?? expr1

Ternary operator

The expression before the '?' is evaluated to a number. If it evaluates to TRUE, the result is the value of the expression between the '?' and ':', otherwise the result is the value of the expression after the ':'. Example:

:echo lnum == 1 ? "top" : lnum

Since the first expression is an "expr2", it cannot contain another ?:. The other two expressions can, thus allow for recursive use of ?:. Example:

:echo lnum == 1 ? "top" : lnum == 1000 ? "last" : lnum

To keep this readable, using line-continuation is suggested:

:echo lnum == 1
:\	? "top"
:\	: lnum == 1000
:\		? "last"
:\		: lnum

You should always put a space before the ':', otherwise it can be mistaken for use in a variable such as "a:1".

Falsy operator

This is also known as the "null coalescing operator", but that's too complicated, thus we just call it the falsy operator.

The expression before the '??' is evaluated. If it evaluates to truthy, this is used as the result. Otherwise the expression after the '??' is evaluated and used as the result. This is most useful to have a default value for an expression that may result in zero or empty:

echo theList ?? 'list is empty'
echo GetName() ?? 'unknown'

These are similar, but not equal:

expr2 ?? expr1
expr2 ? expr2 : expr1

In the second line "expr2" is evaluated twice.

expr2 and expr3 expr2 expr3

expr3 || expr3 .. logical OR expr-barbar
expr4 && expr4 .. logical AND expr-&&

The "||" and "&&" operators take one argument on each side. The arguments are (converted to) Numbers. The result is:

input output

n1 n2 n1 || n2 n1 && n2

FALSE FALSE FALSE FALSE FALSE TRUE TRUE FALSE TRUE FALSE TRUE FALSE TRUE TRUE TRUE TRUE

The operators can be concatenated, for example:

&nu || &list && &shell == "csh"

Note that "&&" takes precedence over "||", so this has the meaning of:

&nu || (&list && &shell == "csh")

Once the result is known, the expression "short-circuits", that is, further arguments are not evaluated. This is like what happens in C. For example:

let a = 1
echo a || b

This is valid even if there is no variable called "b" because "a" is TRUE, so the result must be TRUE. Similarly below:

echo exists("b") && b == "yes"

This is valid whether "b" has been defined or not. The second clause will only be evaluated if "b" has been defined.

expr4 expr4

expr5 {cmp} expr5

Compare two expr5 expressions, resulting in a 0 if it evaluates to false, or 1 if it evaluates to true.

expr-== expr-!= expr-> expr->=
expr-< expr-<= expr-=~ expr-!~ expr-==# expr-!=# expr-># expr->=# expr-<# expr-<=# expr-=~# expr-!~# expr-==? expr-!=? expr->? expr->=? expr-<? expr-<=? expr-=~? expr-!~? expr-is expr-isnot expr-is# expr-isnot# expr-is? expr-isnot?

use 'ignorecase' match case ignore case

equal == ==# ==? not equal != !=# !=? greater than > ># >? greater than or equal >= >=# >=? smaller than < <# <? smaller than or equal <= <=# <=? regexp matches =~ =~# =~? regexp doesn't match !~ !~# !~? same instance is is# is? different instance isnot isnot# isnot?

Examples: "abc" ==# "Abc" evaluates to 0 "abc" ==? "Abc" evaluates to 1 "abc" == "Abc" evaluates to 1 if 'ignorecase' is set, 0 otherwise

E691 E692 A List can only be compared with a List and only "equal", "not equal", "is" and "isnot" can be used. This compares the values of the list, recursively. Ignoring case means case is ignored when comparing item values.

E735 E736 A Dictionary can only be compared with a Dictionary and only "equal", "not equal", "is" and "isnot" can be used. This compares the key/values of the Dictionary recursively. Ignoring case means case is ignored when comparing item values.

E694
A Funcref can only be compared with a Funcref and only "equal", "not equal", "is" and "isnot" can be used. Case is never ignored. Whether arguments or a Dictionary are bound (with a partial) matters. The Dictionaries must also be equal (or the same, in case of "is") and the arguments must be equal (or the same).

To compare Funcrefs to see if they refer to the same function, ignoring bound Dictionary and arguments, use get() to get the function name:

if get(Part1, 'name') == get(Part2, 'name')
   " Part1 and Part2 refer to the same function

Using "is" or "isnot" with a List, Dictionary or Blob checks whether the expressions are referring to the same List, Dictionary or Blob instance. A copy of a List is different from the original List. When using "is" without a List, Dictionary or Blob, it is equivalent to using "equal", using "isnot" is equivalent to using "not equal". Except that a different type means the values are different:

echo 4 == '4'
1
echo 4 is '4'
0
echo 0 is []
0

"is#"/"isnot#" and "is?"/"isnot?" can be used to match and ignore case.

When comparing a String with a Number, the String is converted to a Number, and the comparison is done on Numbers. This means that:

echo 0 == 'x'
1

because 'x' converted to a Number is zero. However:

echo [0] == ['x']
0

Inside a List or Dictionary this conversion is not used.

When comparing two Strings, this is done with strcmp() or stricmp(). This results in the mathematical difference (comparing byte values), not necessarily the alphabetical difference in the local language.

When using the operators with a trailing '#', or the short version and 'ignorecase' is off, the comparing is done with strcmp(): case matters.

When using the operators with a trailing '?', or the short version and 'ignorecase' is set, the comparing is done with stricmp(): case is ignored.

'smartcase' is not used.

The "=~" and "!~" operators match the lefthand argument with the righthand argument, which is used as a pattern. See pattern for what a pattern is. This matching is always done like 'magic' was set and 'cpoptions' is empty, no matter what the actual value of 'magic' or 'cpoptions' is. This makes scripts portable. To avoid backslashes in the regexp pattern to be doubled, use a single-quote string, see literal-string. Since a string is considered to be a single line, a multi-line pattern (containing \n, backslash-n) will not match. However, a literal NL character can be matched like an ordinary character. Examples: "foo\nbar" =~ "\n" evaluates to 1 "foo\nbar" =~ "\\n" evaluates to 0

expr5 and expr6 expr5 expr6

expr6 + expr6 Number addition, List or Blob concatenation expr-+ expr6 - expr6 Number subtraction expr--
expr6 . expr6 String concatenation expr-.
expr6 .. expr6 String concatenation expr-..

For Lists only "+" is possible and then both expr6 must be a list. The result is a new list with the two lists Concatenated.

For String concatenation ".." is preferred, since "." is ambiguous, it is also used for Dict member access and floating point numbers.

expr7 * expr7 Number multiplication expr-star
expr7 / expr7 Number division expr-/
expr7 % expr7 Number modulo expr-%

For all, except "." and "..", Strings are converted to Numbers. For bitwise operators see and(), or() and xor().

Note the difference between "+" and ".": "123" + "456" = 579 "123" . "456" = "123456"

Since '.' has the same precedence as '+' and '-', you need to read:

1 . 90 + 90.0

As:

(1 . 90) + 90.0

That works, since the String "190" is automatically converted to the Number 190, which can be added to the Float 90.0. However:

1 . 90 * 90.0

Should be read as:

1 . (90 * 90.0)

Since '.' has lower precedence than "*". This does NOT work, since this attempts to concatenate a Float and a String.

When dividing a Number by zero the result depends on the value: 0 / 0 = -0x80000000 (like NaN for Float) >0 / 0 = 0x7fffffff (like positive infinity) <0 / 0 = -0x7fffffff (like negative infinity) (before Vim 7.2 it was always 0x7fffffff)

When 64-bit Number support is enabled: 0 / 0 = -0x8000000000000000 (like NaN for Float) >0 / 0 = 0x7fffffffffffffff (like positive infinity) <0 / 0 = -0x7fffffffffffffff (like negative infinity)

When the righthand side of '%' is zero, the result is 0.

None of these work for Funcrefs.

. and % do not work for Float. E804

expr7 expr7

! expr7 logical NOT expr-!

expr7 unary minus expr-unary--
+ expr7 unary plus expr-unary-+

For '!' TRUE becomes FALSE, FALSE becomes TRUE (one). For '-' the sign of the number is changed. For '+' the number is unchanged. Note: "++" has no effect.

A String will be converted to a Number first.

These three can be repeated and mixed. Examples: !-1 == 0 !!8 == 1 --9 == 9

expr8 expr8

This expression is either expr9 or a sequence of the alternatives below, in any order. E.g., these are all possible: expr8[expr1].name expr8.name[expr1] expr8(expr1, ...)[expr1].name expr8->(expr1, ...)[expr1] Evaluation is always from left to right.

expr8[expr1] item of String or List expr-[] E111 subscript
In legacy Vim script: If expr8 is a Number or String this results in a String that contains the expr1'th single byte from expr8. expr8 is used as a String (a number is automatically converted to a String), expr1 as a Number. This doesn't recognize multibyte encodings, see byteidx() for an alternative, or use split() to turn the string into a list of characters. Example, to get the byte under the cursor:

:let c = getline(".")[col(".") - 1]

Index zero gives the first byte. This is like it works in C. Careful: text column numbers start with one! Example, to get the byte under the cursor:

:let c = getline(".")[col(".") - 1]

Index zero gives the first byte. Careful: text column numbers start with one!

If the length of the String is less than the index, the result is an empty String. A negative index always results in an empty string (reason: backward compatibility). Use [-1:] to get the last byte.

If expr8 is a List then it results the item at index expr1. See list-index for possible index values. If the index is out of range this results in an error. Example:

:let item = mylist[-1]		" get last item

Generally, if a List index is equal to or higher than the length of the List, or more negative than the length of the List, this results in an error.

expr8[expr1a : expr1b] substring or sublist expr-[:] substring

If expr8 is a String this results in the substring with the bytes or characters from expr1a to and including expr1b. expr8 is used as a String, expr1a and expr1b are used as a Number.

In legacy Vim script the indexes are byte indexes. This doesn't recognize multibyte encodings, see byteidx() for computing the indexes. If expr8 is a Number it is first converted to a String.

The item at index expr1b is included, it is inclusive. For an exclusive index use the slice() function.

If expr1a is omitted zero is used. If expr1b is omitted the length of the string minus one is used.

A negative number can be used to measure from the end of the string. -1 is the last character, -2 the last but one, etc.

If an index goes out of range for the string characters are omitted. If expr1b is smaller than expr1a the result is an empty string.

Examples:

:let c = name[-1:]		" last byte of a string
:let c = name[0:-1]		" the whole string
:let c = name[-2:-2]		" last but one byte of a string
:let s = line(".")[4:]		" from the fifth byte to the end
:let s = s[:-3]			" remove last two bytes

slice
If expr8 is a List this results in a new List with the items indicated by the indexes expr1a and expr1b. This works like with a String, as explained just above. Also see sublist below. Examples:

:let l = mylist[:3]		" first four items
:let l = mylist[4:4]		" List with one item
:let l = mylist[:]		" shallow copy of a List

If expr8 is a Blob this results in a new Blob with the bytes in the indexes expr1a and expr1b, inclusive. Examples:

:let b = 0zDEADBEEF
:let bs = b[1:2]		" 0zADBE
:let bs = b[]			" copy of 0zDEADBEEF

Using expr8[expr1] or expr8[expr1a : expr1b] on a Funcref results in an error.

Watch out for confusion between a namespace and a variable followed by a colon for a sublist:

mylist[n:]     " uses variable n
mylist[s:]     " uses namespace s:, error!

expr8.name entry in a Dictionary expr-entry

If expr8 is a Dictionary and it is followed by a dot, then the following name will be used as a key in the Dictionary. This is just like: expr8[name].

The name must consist of alphanumeric characters, just like a variable name, but it may start with a number. Curly braces cannot be used.

There must not be white space before or after the dot.

Examples:

:let dict = {"one": 1, 2: "two"}
:echo dict.one		" shows "1"
:echo dict.2		" shows "two"
:echo dict .2		" error because of space before the dot

Note that the dot is also used for String concatenation. To avoid confusion always put spaces around the dot for String concatenation.

expr8(expr1, ...) Funcref function call E1085

When expr8 is a Funcref type variable, invoke the function it refers to.

expr8->name([args]) method call method -> expr8->{lambda}([args])

E260 E276 For methods that are also available as global functions this is the same as:

name(expr8 [, args])

There can also be methods specifically for the type of "expr8".

This allows for chaining, passing the value that one method returns to the next method:

mylist->filter(filterexpr)->map(mapexpr)->sort()->join()

Example of using a lambda:

GetPercentage()->{x -> x * 100}()->printf('%d%%')

When using -> the expr7 operators will be applied first, thus:

-1.234->string()

Is equivalent to:

(-1.234)->string()

And NOT:

-(1.234->string())

E274
"->name(" must not contain white space. There can be white space before the "->" and after the "(", thus you can split the lines like this:

mylist
\ ->filter(filterexpr)
\ ->map(mapexpr)
\ ->sort()
\ ->join()

When using the lambda form there must be no white space between the } and the

(.

expr9

number

number number constant expr-number

0x hex-number 0o octal-number binary-number Decimal, Hexadecimal (starting with 0x or 0X), Binary (starting with 0b or 0B) and Octal (starting with 0, 0o or 0O).

floating-point-format
Floating point numbers can be written in two forms:

[-+]{N}.{M} [-+]{N}.{M}[eE][-+]{exp}

{N} and {M} are numbers. Both {N} and {M} must be present and can only contain digits. [-+] means there is an optional plus or minus sign. {exp} is the exponent, power of 10. Only a decimal point is accepted, not a comma. No matter what the current locale is.

Examples: 123.456 +0.0001 55.0 -0.123 1.234e03 1.0E-6 -3.1416e+88

These are INVALID: 3. empty {M} 1e40 missing .{M}

Rationale: Before floating point was introduced, the text "123.456" was interpreted as the two numbers "123" and "456", both converted to a string and concatenated, resulting in the string "123456". Since this was considered pointless, and we could not find it intentionally being used in Vim scripts, this backwards incompatibility was accepted in favor of being able to use the normal notation for floating point numbers.

float-pi float-e A few useful values to copy&paste:

:let pi = 3.14159265359
:let e  = 2.71828182846

Or, if you don't want to write them in as floating-point literals, you can also use functions, like the following:

:let pi = acos(-1.0)
:let e  = exp(1.0)

floating-point-precision
The precision and range of floating points numbers depends on what "double" means in the library Vim was compiled with. There is no way to change this at runtime.

The default for displaying a Float is to use 6 decimal places, like using printf("%g", f). You can select something else when using the printf() function. Example:

:echo printf('%.15e', atan(1))

7.853981633974483e-01

string string String expr-string E114

"string" string constant expr-quote

Note that double quotes are used.

A string constant accepts these special characters: \... three-digit octal number (e.g., "\316") \.. two-digit octal number (must be followed by non-digit) \. one-digit octal number (must be followed by non-digit) \x.. byte specified with two hex numbers (e.g., "\x1f") \x. byte specified with one hex number (must be followed by non-hex char) \X.. same as \x.. \X. same as \x. \u.... character specified with up to 4 hex numbers, stored as UTF-8 (e.g., "\u02a4") \U.... same as \u but allows up to 8 hex numbers. \b backspace <BS> \e escape <Esc> \f formfeed 0x0C \n newline <NL> \r return <CR> \t tab <Tab> \\ backslash \" double quote \<xxx> Special key named "xxx". e.g. "\<C-W>" for CTRL-W. This is for use in mappings, the 0x80 byte is escaped. To use the double quote character it must be escaped: "<M-\">". Don't use <Char-xxxx> to get a UTF-8 character, use \uxxxx as mentioned above. \<*xxx> Like \<xxx> but prepends a modifier instead of including it in the character. E.g. "\<C-w>" is one character 0x17 while "\<*C-w>" is four bytes: 3 for the CTRL modifier and then character "W".

Note that "\xff" is stored as the byte 255, which may be invalid in some encodings. Use "\u00ff" to store character 255 correctly as UTF-8.

Note that "\000" and "\x00" force the end of the string.

blob-literal blob-literal E973

Hexadecimal starting with 0z or 0Z, with an arbitrary number of bytes. The sequence must be an even number of hex characters. Example:

:let b = 0zFF00ED015DAF

literal-string literal-string E115

string string constant expr-'

Note that single quotes are used.

This string is taken as it is. No backslashes are removed or have a special meaning. The only exception is that two quotes stand for one quote.

Single quoted strings are useful for patterns, so that backslashes do not need to be doubled. These two commands are equivalent:

if a =~ "\\s*"
if a =~ '\s*'

interpolated-string $quote interpolated-string

$"string" interpolated string constant expr-$quote
$'string' interpolated literal string constant expr-$'

Interpolated strings are an extension of the string and literal-string, allowing the inclusion of Vim script expressions (see expr1). Any expression returning a value can be enclosed between curly braces. The value is converted to a string. All the text and results of the expressions are concatenated to make a new string. E1278
To include an opening brace '{' or closing brace '}' in the string content double it. For double quoted strings using a backslash also works. A single closing brace '}' will result in an error.

Examples:

let your_name = input("What's your name? ")

What's your name? Peter

echo
echo $"Hello, {your_name}!"

Hello, Peter!

echo $"The square root of {{9}} is {sqrt(9)}"

The square root of {9} is 3.0

string-offset-encoding
A string consists of multiple characters. UTF-8 uses one byte for ASCII characters, two bytes for other latin characters and more bytes for other characters.

A string offset can count characters or bytes. Other programs may use UTF-16 encoding (16-bit words) and an offset of UTF-16 words. Some functions use byte offsets, usually for UTF-8 encoding. Other functions use character offsets, in which case the encoding doesn't matter.

The different offsets for the string "a©😊" are below:

UTF-8 offsets: [0]: 61, [1]: C2, [2]: A9, [3]: F0, [4]: 9F, [5]: 98, [6]: 8A UTF-16 offsets: [0]: 0061, [1]: 00A9, [2]: D83D, [3]: DE0A UTF-32 (character) offsets: [0]: 00000061, [1]: 000000A9, [2]: 0001F60A

You can use the "g8" and "ga" commands on a character to see the decimal/hex/octal values.

The functions byteidx(), utf16idx() and charidx() can be used to convert between these indices. The functions strlen(), strutf16len() and strcharlen() return the number of bytes, UTF-16 code units and characters in a string respectively.

option expr-option E112 E113

&option option value, local value if possible &g:option global option value &l:option local option value

Examples:

echo "tabstop is " .. &tabstop
if &expandtab

Any option name can be used here. See options. When using the local value and there is no buffer-local or window-local value, the global value is used anyway.

register expr-register @r

@r contents of register 'r'

The result is the contents of the named register, as a single string. Newlines are inserted where required. To get the contents of the unnamed register use @" or @@. See registers for an explanation of the available registers.

When using the '=' register you get the expression itself, not what it evaluates to. Use eval() to evaluate it.

nesting expr-nesting E110 ------- (expr1) nested expression

environment variable expr-env

$VAR environment variable

The String value of any environment variable. When it is not defined, the result is an empty string.

The functions getenv() and setenv() can also be used and work for environment variables with non-alphanumeric names. The function environ() can be used to get a Dict with all environment variables.

expr-env-expand
Note that there is a difference between using $VAR directly and using expand("$VAR"). Using it directly will only expand environment variables that are known inside the current Vim session. Using expand() will first try using the environment variables known inside the current Vim session. If that fails, a shell will be used to expand the variable. This can be slow, but it does expand all variables that the shell knows about. Example:

:echo $shell
:echo expand("$shell")

The first one probably doesn't echo anything, the second echoes the $shell variable (if your shell supports it).

internal variable expr-variable

variable internal variable See below internal-variables.

function call expr-function E116 E118 E119 E120

function(expr1, ...) function call See below functions.

lambda expression expr-lambda lambda

{args -> expr1} lambda expression E451

A lambda expression creates a new unnamed function which returns the result of evaluating expr1. Lambda expressions differ from user-functions in the following ways:

1. The body of the lambda expression is an expr1 and not a sequence of Ex commands. 2. The prefix "a:" should not be used for arguments. E.g.:

:let F = {arg1, arg2 -> arg1 - arg2}
:echo F(5, 2)

The arguments are optional. Example:

:let F = {-> 'error function'}
:echo F('ignored')

error function closure
Lambda expressions can access outer scope variables and arguments. This is often called a closure. Example where "i" and "a:arg" are used in a lambda while they already exist in the function scope. They remain valid even after the function returns:

:function Foo(arg)
:  let i = 3
:  return {x -> x + i - a:arg}
:endfunction
:let Bar = Foo(4)
:echo Bar(6)

5 Note that the variables must exist in the outer scope before the lambda is defined for this to work. See also :func-closure.

Lambda and closure support can be checked with:

if has('lambda')

Examples for using a lambda expression with sort(), map() and filter():

:echo map([1, 2, 3], {idx, val -> val + 1})

[2, 3, 4]

:echo sort([3,7,2,1,4], {a, b -> a - b})

[1, 2, 3, 4, 7]

The lambda expression is also useful for jobs and timers:

:let timer = timer_start(500,
                \ {-> execute("echo 'Handler called'", "")},
                \ {'repeat': 3})

Handler called Handler called Handler called

Note that it is possible to cause memory to be used and not freed if the closure is referenced by the context it depends on:

function Function()
   let x = 0
   let F = {-> x}
 endfunction

The closure uses "x" from the function scope, and "F" in that same scope refers to the closure. This cycle results in the memory not being freed. Recommendation: don't do this.

Notice how execute() is used to execute an Ex command. That's ugly though.

Lambda expressions have internal names like '<lambda>42'. If you get an error for a lambda expression, you can find what it is with the following command:

:function <lambda>42

3. Internal variable internal-variables E461

An internal variable name can be made up of letters, digits and '_'. But it cannot start with a digit. It's also possible to use curly braces, see curly-braces-names.

An internal variable is created with the ":let" command :let. An internal variable is explicitly destroyed with the ":unlet" command :unlet. Using a name that is not an internal variable or refers to a variable that has been destroyed results in an error.

variable-scope
There are several name spaces for variables. Which one is to be used is specified by what is prepended:

(nothing) In a function: local to a function; otherwise: global buffer-variable b: Local to the current buffer. window-variable w: Local to the current window. tabpage-variable t: Local to the current tab page. global-variable g: Global. local-variable l: Local to a function. script-variable s: Local to a :sourced Vim script. function-argument a: Function argument (only inside a function). vim-variable v: Global, predefined by Vim.

The scope name by itself can be used as a Dictionary. For example, to delete all script-local variables:

:for k in keys(s:)
:    unlet s:[k]
:endfor

buffer-variable b:var b: A variable name that is preceded with "b:" is local to the current buffer. Thus you can have several "b:foo" variables, one for each buffer. This kind of variable is deleted when the buffer is wiped out or deleted with :bdelete.

One local buffer variable is predefined: b:changedtick changetick b:changedtick The total number of changes to the current buffer. It is incremented for each change. An undo command is also a change in this case. Resetting 'modified' when writing the buffer is also counted. This can be used to perform an action only when the buffer has changed. Example:

:if my_changedtick != b:changedtick
:	let my_changedtick = b:changedtick
:	call My_Update()
:endif

You cannot change or delete the b:changedtick variable.

window-variable w:var w: A variable name that is preceded with "w:" is local to the current window. It is deleted when the window is closed.

tabpage-variable t:var t: A variable name that is preceded with "t:" is local to the current tab page, It is deleted when the tab page is closed.

global-variable g:var g: Inside functions global variables are accessed with "g:". Omitting this will access a variable local to a function. But "g:" can also be used in any other place if you like.

local-variable l:var l: Inside functions local variables are accessed without prepending anything. But you can also prepend "l:" if you like. However, without prepending "l:" you may run into reserved variable names. For example "count". By itself it refers to "v:count". Using "l:count" you can have a local variable with the same name.

script-variable s:var In a Vim script variables starting with "s:" can be used. They cannot be accessed from outside of the scripts, thus are local to the script.

They can be used in:

commands executed while the script is sourced

functions defined in the script

autocommands defined in the script

functions and autocommands defined in functions and autocommands which were defined in the script (recursively)

user defined commands defined in the script Thus not in:

other scripts sourced from this one

mappings

menus

etc.

Script variables can be used to avoid conflicts with global variable names. Take this example:

let s:counter = 0
function MyCounter()
  let s:counter = s:counter + 1
  echo s:counter
endfunction
command Tick call MyCounter()

You can now invoke "Tick" from any script, and the "s:counter" variable in that script will not be changed, only the "s:counter" in the script where "Tick" was defined is used.

Another example that does the same:

let s:counter = 0
command Tick let s:counter = s:counter + 1 | echo s:counter

When calling a function and invoking a user-defined command, the context for script variables is set to the script where the function or command was defined.

The script variables are also available when a function is defined inside a function that is defined in a script. Example:

let s:counter = 0
function StartCounting(incr)
  if a:incr
    function MyCounter()
      let s:counter = s:counter + 1
    endfunction
  else
    function MyCounter()
      let s:counter = s:counter - 1
    endfunction
  endif
endfunction

This defines the MyCounter() function either for counting up or counting down when calling StartCounting(). It doesn't matter from where StartCounting() is called, the s:counter variable will be accessible in MyCounter().

When the same script is sourced again it will use the same script variables. They will remain valid as long as Vim is running. This can be used to maintain a counter:

if !exists("s:counter")
  let s:counter = 1
  echo "script executed for the first time"
else
  let s:counter = s:counter + 1
  echo "script executed " .. s:counter .. " times now"
endif

Note that this means that filetype plugins don't get a different set of script variables for each buffer. Use local buffer variables instead b:var.

PREDEFINED VIM VARIABLES vim-variable v:var v:

E963

The alphabetic list of all builtin variables and details are in a separate help file: vvars.

4. Builtin Functions vim-function functions

The Vimscript subsystem (referred to as "eval" internally) provides builtin functions. Scripts can also define user-functions.

See function-list to browse functions by topic.

The alphabetic list of all builtin functions and details are in a separate help file: builtin-functions.

5. Defining functions user-function

New functions can be defined. These can be called just like builtin functions. The function takes arguments, executes a sequence of Ex commands and can return a value.

You can find most information about defining functions in userfunc.txt.

6. Curly braces names curly-braces-names

In most places where you can use a variable, you can use a "curly braces name" variable. This is a regular variable name with one or more expressions wrapped in braces {} like this:

my_{adjective}_variable

When Vim encounters this, it evaluates the expression inside the braces, puts that in place of the expression, and re-interprets the whole as a variable name. So in the above example, if the variable "adjective" was set to "noisy", then the reference would be to "my_noisy_variable", whereas if "adjective" was set to "quiet", then it would be to "my_quiet_variable".

One application for this is to create a set of variables governed by an option value. For example, the statement

echo my_{&background}_message

would output the contents of "my_dark_message" or "my_light_message" depending on the current value of 'background'.

You can use multiple brace pairs:

echo my_{adverb}_{adjective}_message

..or even nest them:

echo my_{ad{end_of_word}}_message

where "end_of_word" is either "verb" or "jective".

However, the expression inside the braces must evaluate to a valid single variable name, e.g. this is invalid:

:let foo='a + b'
:echo c{foo}d

.. since the result of expansion is "ca + bd", which is not a variable name.

curly-braces-function-names
You can call and define functions by an evaluated name in a similar way. Example:

:let func_end='whizz'
:call my_func_{func_end}(parameter)

This would call the function "my_func_whizz(parameter)".

This does NOT work:

:let i = 3
:let @{i} = ''  " error
:echo @{i}      " error

7. Commands expression-commands

:let {var-name} = {expr1} :let E18 Set internal variable {var-name} to the result of the expression {expr1}. The variable will get the type from the {expr}. If {var-name} didn't exist yet, it is created.

:let {var-name}[{idx}] = {expr1} E689
Set a list item to the result of the expression {expr1}. {var-name} must refer to a list and {idx} must be a valid index in that list. For nested list the index can be repeated. This cannot be used to add an item to a List. This cannot be used to set a byte in a String. You can do that like this:

:let var = var[0:2] .. 'X' .. var[4:]

When {var-name} is a Blob then {idx} can be the length of the blob, in which case one byte is appended.

E711 E719 :let {var-name}[{idx1}:{idx2}] = {expr1} E708 E709 E710 Set a sequence of items in a List to the result of the expression {expr1}, which must be a list with the correct number of items. {idx1} can be omitted, zero is used instead. {idx2} can be omitted, meaning the end of the list. When the selected range of items is partly past the end of the list, items will be added.

:let+= :let-= :letstar= :let/= :let%= :let.= :let..= E734 :let {var} += {expr1} Like ":let {var} = {var} + {expr1}". :let {var} -= {expr1} Like ":let {var} = {var} - {expr1}". :let {var} *= {expr1} Like ":let {var} = {var} * {expr1}". :let {var} /= {expr1} Like ":let {var} = {var} / {expr1}". :let {var} %= {expr1} Like ":let {var} = {var} % {expr1}". :let {var} .= {expr1} Like ":let {var} = {var} . {expr1}". :let {var} ..= {expr1} Like ":let {var} = {var} .. {expr1}". These fail if {var} was not set yet and when the type of {var} and {expr1} don't fit the operator. += modifies a List or a Blob in-place instead of creating a new one.

:let ${env-name} = {expr1} :let-environment :let-$ Set environment variable {env-name} to the result of the expression {expr1}. The type is always String. :let ${env-name} .= {expr1} Append {expr1} to the environment variable {env-name}. If the environment variable didn't exist yet this works like "=".

:let @{reg-name} = {expr1} :let-register :let-@ Write the result of the expression {expr1} in register {reg-name}. {reg-name} must be a single letter, and must be the name of a writable register (see registers). "@@" can be used for the unnamed register, "@/" for the search pattern. If the result of {expr1} ends in a <CR> or <NL>, the register will be linewise, otherwise it will be set to charwise. This can be used to clear the last search pattern:

:let @/ = ""

This is different from searching for an empty string, that would match everywhere.

:let @{reg-name} .= {expr1} Append {expr1} to register {reg-name}. If the register was empty it's like setting it to {expr1}.

:let &{option-name} = {expr1} :let-option :let-& Set option {option-name} to the result of the expression {expr1}. A String or Number value is always converted to the type of the option. For an option local to a window or buffer the effect is just like using the :set command: both the local value and the global value are changed. Example:

:let &path = &path .. ',/usr/local/include'

:let &{option-name} .= {expr1} For a string option: Append {expr1} to the value. Does not insert a comma like :set+=.

:let &{option-name} += {expr1} :let &{option-name} -= {expr1} For a number or boolean option: Add or subtract {expr1}.

:let &l:{option-name} = {expr1} :let &l:{option-name} .= {expr1} :let &l:{option-name} += {expr1} :let &l:{option-name} -= {expr1} Like above, but only set the local value of an option (if there is one). Works like :setlocal.

:let &g:{option-name} = {expr1} :let &g:{option-name} .= {expr1} :let &g:{option-name} += {expr1} :let &g:{option-name} -= {expr1} Like above, but only set the global value of an option (if there is one). Works like :setglobal.

:let [{name1}, {name2}, ...] = {expr1} :let-unpack E687 E688 {expr1} must evaluate to a List. The first item in the list is assigned to {name1}, the second item to {name2}, etc. The number of names must match the number of items in the List. Each name can be one of the items of the ":let" command as mentioned above. Example:

:let [s, item] = GetItem(s)

Detail: {expr1} is evaluated first, then the assignments are done in sequence. This matters if {name2} depends on {name1}. Example:

:let x = [0, 1]
:let i = 0
:let [i, x[i]] = [1, 2]
:echo x

The result is [0, 2].

:let [{name1}, {name2}, ...] .= {expr1} :let [{name1}, {name2}, ...] += {expr1} :let [{name1}, {name2}, ...] -= {expr1} Like above, but append/add/subtract the value for each List item.

:let [{name}, ..., ; {lastname}] = {expr1} E452
Like :let-unpack above, but the List may have more items than there are names. A list of the remaining items is assigned to {lastname}. If there are no remaining items {lastname} is set to an empty list. Example:

:let [a, b; rest] = ["aval", "bval", 3, 4]

:let [{name}, ..., ; {lastname}] .= {expr1} :let [{name}, ..., ; {lastname}] += {expr1} :let [{name}, ..., ; {lastname}] -= {expr1} Like above, but append/add/subtract the value for each List item.

:let=<< :let-heredoc E990 E991 E172 E221 E1145 :let {var-name} =<< [trim] [eval] {endmarker} text... text... {endmarker} Set internal variable {var-name} to a List containing the lines of text bounded by the string {endmarker}.

If "eval" is not specified, then each line of text is used as a literal-string, except that single quotes does not need to be doubled. If "eval" is specified, then any Vim expression in the form {expr} is evaluated and the result replaces the expression, like with interpolated-string. Example where $HOME is expanded:

let lines =<< trim eval END
  some text
  See the file {$HOME}/.vimrc
  more text
END

There can be multiple Vim expressions in a single line but an expression cannot span multiple lines. If any expression evaluation fails, then the assignment fails.

{endmarker} must not contain white space. {endmarker} cannot start with a lower case character. The last line should end only with the {endmarker} string without any other character. Watch out for white space after {endmarker}!

Without "trim" any white space characters in the lines of text are preserved. If "trim" is specified before {endmarker}, then indentation is stripped so you can do:

let text =<< trim END
   if ok
     echo 'done'
   endif
END

Results in: ["if ok", " echo 'done'", "endif"] The marker must line up with "let" and the indentation of the first line is removed from all the text lines. Specifically: all the leading indentation exactly matching the leading indentation of the first non-empty text line is stripped from the input lines. All leading indentation exactly matching the leading indentation before let is stripped from the line containing {endmarker}. Note that the difference between space and tab matters here.

If {var-name} didn't exist yet, it is created. Cannot be followed by another command, but can be followed by a comment.

To avoid line continuation to be applied, consider adding 'C' to 'cpoptions':

set cpo+=C
let var =<< END
   \ leading backslash
END
set cpo-=C

Examples:

let var1 =<< END
Sample text 1
    Sample text 2
Sample text 3
END
let data =<< trim DATA
        1 2 3 4
        5 6 7 8
DATA
let code =<< trim eval CODE
   let v = {10 + 20}
   let h = "{$HOME}"
   let s = "{Str1()} abc {Str2()}"
   let n = {MyFunc(3, 4)}
CODE

E121
:let {var-name} .. List the value of variable {var-name}. Multiple variable names may be given. Special names recognized here: E738
g: global variables b: local buffer variables w: local window variables t: local tab page variables s: script-local variables l: local function variables v: Vim variables.

:let List the values of all variables. The type of the variable is indicated before the value: <nothing> String # Number * Funcref

:unl[et][!] {name} ... :unlet :unl E108 E795 Remove the internal variable {name}. Several variable names can be given, they are all removed. The name may also be a List or Dictionary item. With [!] no error message is given for non-existing variables. One or more items from a List can be removed:

:unlet list[3]	  " remove fourth item
:unlet list[3:]   " remove fourth item to last

One item from a Dictionary can be removed at a time:

:unlet dict['two']
:unlet dict.two

This is especially useful to clean up used global variables and script-local variables (these are not deleted when the script ends). Function-local variables are automatically deleted when the function ends.

:unl[et] ${env-name} ... :unlet-environment :unlet-$ Remove environment variable {env-name}. Can mix {name} and ${env-name} in one :unlet command. No error message is given for a non-existing variable, also without !. If the system does not support deleting an environment variable, it is made empty.

:cons :const :cons[t] {var-name} = {expr1} :cons[t] [{name1}, {name2}, ...] = {expr1} :cons[t] [{name}, ..., ; {lastname}] = {expr1} :cons[t] {var-name} =<< [trim] [eval] {marker} text... text... {marker} Similar to :let, but additionally lock the variable after setting the value. This is the same as locking the variable with :lockvar just after :let, thus:

:const x = 1

is equivalent to:

:let x = 1
:lockvar! x

This is useful if you want to make sure the variable is not modified. If the value is a List or Dictionary literal then the items also cannot be changed:

const ll = [1, 2, 3]
let ll[1] = 5  " Error!

Nested references are not locked:

let lvar = ['a']
const lconst = [0, lvar]
let lconst[0] = 2  " Error!
let lconst[1][0] = 'b'  " OK

E995
It is an error to specify an existing variable with :const.

:let x = 1
:const x = 1  " Error!

E996
Note that environment variables, option values and register values cannot be used here, since they cannot be locked.

:cons[t] :cons[t] {var-name} If no argument is given or only {var-name} is given, the behavior is the same as :let.

:lockv[ar][!] [depth] {name} ... :lockvar :lockv Lock the internal variable {name}. Locking means that it can no longer be changed (until it is unlocked). A locked variable can be deleted:

:lockvar v
:let v = 'asdf'	  " fails!
:unlet v	  " works

E741 E940 E1122 If you try to change a locked variable you get an error message: "E741: Value is locked: {name}". If you try to lock or unlock a built-in variable you will get an error message "E940: Cannot lock or unlock variable {name}".

[depth] is relevant when locking a List or Dictionary. It specifies how deep the locking goes: 0 Lock the variable {name} but not its value. 1 Lock the List or Dictionary itself, cannot add or remove items, but can still change their values. 2 Also lock the values, cannot change the items. If an item is a List or Dictionary, cannot add or remove items, but can still change the values. 3 Like 2 but for the List / Dictionary in the List / Dictionary, one level deeper. The default [depth] is 2, thus when {name} is a List or Dictionary the values cannot be changed.

Example with [depth] 0:

let mylist = [1, 2, 3]
lockvar 0 mylist
let mylist[0] = 77	" OK
call add(mylist, 4)	" OK
let mylist = [7, 8, 9]  " Error!

E743
For unlimited depth use [!] and omit [depth]. However, there is a maximum depth of 100 to catch loops.

Note that when two variables refer to the same List and you lock one of them, the List will also be locked when used through the other variable. Example:

:let l = [0, 1, 2, 3]
:let cl = l
:lockvar l
:let cl[1] = 99		" won't work!

You may want to make a copy of a list to avoid this. See deepcopy().

:unlo[ckvar][!] [depth] {name} ... :unlockvar :unlo Unlock the internal variable {name}. Does the opposite of :lockvar.

No error is given if {name} does not exist.

:if {expr1} :if :end :endif :en E171 E579 E580 :en[dif] Execute the commands until the next matching :else or :endif if {expr1} evaluates to non-zero. Although the short forms work, it is recommended to always use :endif to avoid confusion and to make auto-indenting work properly.

From Vim version 4.5 until 5.0, every Ex command in between the :if and :endif is ignored. These two commands were just to allow for future expansions in a backward compatible way. Nesting was allowed. Note that any :else or :elseif was ignored, the else part was not executed either.

You can use this to remain compatible with older versions:

:if version >= 500
:  version-5-specific-commands
:endif

The commands still need to be parsed to find the endif. Sometimes an older Vim has a problem with a new command. For example, :silent is recognized as a :substitute command. In that case :execute can avoid problems:

:if version >= 600
:  execute "silent 1,$delete"
:endif

NOTE: The :append and :insert commands don't work properly in between :if and :endif.

:else :el E581 E583 :el[se] Execute the commands until the next matching :else or :endif if they previously were not being executed.

:elseif :elsei E582 E584 :elsei[f] {expr1} Short for :else :if, with the addition that there is no extra :endif.

:wh[ile] {expr1} :while :endwhile :wh :endw E170 E585 E588 E733 :endw[hile] Repeat the commands between :while and :endwhile, as long as {expr1} evaluates to non-zero. When an error is detected from a command inside the loop, execution continues after the endwhile. Example:

:let lnum = 1
:while lnum <= line("$")
   :call FixLine(lnum)
   :let lnum = lnum + 1
:endwhile

NOTE: The :append and :insert commands don't work properly inside a :while and :for loop.

:for {var} in {object} :for E690 E732 :endfo[r] :endfo :endfor Repeat the commands between :for and :endfor for each item in {object}. {object} can be a List, a Blob or a String.

Variable {var} is set to the value of each item.

When an error is detected for a command inside the loop, execution continues after the endfor. Changing {object} inside the loop affects what items are used. Make a copy if this is unwanted:

:for item in copy(mylist)

When {object} is a List and not making a copy, Vim stores a reference to the next item in the List before executing the commands with the current item. Thus the current item can be removed without effect. Removing any later item means it will not be found. Thus the following example works (an inefficient way to make a List empty):

for item in mylist
   call remove(mylist, 0)
endfor

Note that reordering the List (e.g., with sort() or reverse()) may have unexpected effects.

When {object} is a Blob, Vim always makes a copy to iterate over. Unlike with List, modifying the Blob does not affect the iteration.

When {object} is a String each item is a string with one character, plus any combining characters.

:for [{var1}, {var2}, ...] in {listlist} :endfo[r] Like :for above, but each item in {listlist} must be a list, of which each item is assigned to {var1}, {var2}, etc. Example:

:for [lnum, col] in [[1, 3], [2, 5], [3, 8]]
   :echo getline(lnum)[col]
:endfor

:continue :con E586 :con[tinue] When used inside a :while or :for loop, jumps back to the start of the loop.

If it is used after a :try inside the loop but before the matching :finally (if present), the commands following the :finally up to the matching :endtry are executed first. This process applies to all nested :trys inside the loop. The outermost :endtry then jumps back to the start of the loop.

:break :brea E587 :brea[k] When used inside a :while or :for loop, skips to the command after the matching :endwhile or :endfor. If it is used after a :try inside the loop but before the matching :finally (if present), the commands following the :finally up to the matching :endtry are executed first. This process applies to all nested :trys inside the loop. The outermost :endtry then jumps to the command after the loop.

:try :try :endt :endtry E600 E601 E602 :endt[ry] Change the error handling for the commands between :try and :endtry including everything being executed across :source commands, function calls, or autocommand invocations.

When an error or interrupt is detected and there is a :finally command following, execution continues after the :finally. Otherwise, or when the :endtry is reached thereafter, the next (dynamically) surrounding :try is checked for a corresponding :finally etc. Then the script processing is terminated. Whether a function definition has an "abort" argument does not matter. Example:

try | call Unknown() | finally | echomsg "cleanup" | endtry
echomsg "not reached"

Moreover, an error or interrupt (dynamically) inside :try and :endtry is converted to an exception. It can be caught as if it were thrown by a :throw command (see :catch). In this case, the script processing is not terminated.

The value "Vim:Interrupt" is used for an interrupt exception. An error in a Vim command is converted to a value of the form "Vim({command}):{errmsg}", other errors are converted to a value of the form "Vim:{errmsg}". {command} is the full command name, and {errmsg} is the message that is displayed if the error exception is not caught, always beginning with the error number. Examples:

try | sleep 100 | catch /^Vim:Interrupt$/ | endtry
try | edit | catch /^Vim(edit):E\d\+/ | echo "error" | endtry

:cat :catch E603 E604 E605 :cat[ch] /{pattern}/ The following commands until the next :catch, :finally, or :endtry that belongs to the same :try as the :catch are executed when an exception matching {pattern} is being thrown and has not yet been caught by a previous :catch. Otherwise, these commands are skipped. When {pattern} is omitted all errors are caught. Examples:

:catch /^Vim:Interrupt$/	 " catch interrupts (CTRL-C)
:catch /^Vim\%((\a\+)\)\=:E/	 " catch all Vim errors
:catch /^Vim\%((\a\+)\)\=:/	 " catch errors and interrupts
:catch /^Vim(write):/		 " catch all errors in :write
:catch /^Vim\%((\a\+)\)\=:E123:/ " catch error E123
:catch /my-exception/		 " catch user exception
:catch /.*/			 " catch everything
:catch				 " same as /.*/

Another character can be used instead of / around the {pattern}, so long as it does not have a special meaning (e.g., '|' or '"') and doesn't occur inside {pattern}. Information about the exception is available in v:exception. Also see throw-variables. NOTE: It is not reliable to ":catch" the TEXT of an error message because it may vary in different locales.

:fina :finally E606 E607 :fina[lly] The following commands until the matching :endtry are executed whenever the part between the matching :try and the :finally is left: either by falling through to the :finally or by a :continue, :break, :finish, or :return, or by an error or interrupt or exception (see :throw).

:th :throw E608 :th[row] {expr1} The {expr1} is evaluated and thrown as an exception. If the :throw is used after a :try but before the first corresponding :catch, commands are skipped until the first :catch matching {expr1} is reached. If there is no such :catch or if the :throw is used after a :catch but before the :finally, the commands following the :finally (if present) up to the matching :endtry are executed. If the :throw is after the :finally, commands up to the :endtry are skipped. At the :endtry, this process applies again for the next dynamically surrounding :try (which may be found in a calling function or sourcing script), until a matching :catch has been found. If the exception is not caught, the command processing is terminated. Example:

:try | throw "oops" | catch /^oo/ | echo "caught" | endtry

Note that "catch" may need to be on a separate line for when an error causes the parsing to skip the whole line and not see the "|" that separates the commands.

:ec :echo :ec[ho] {expr1} .. Echoes each {expr1}, with a space in between. The first {expr1} starts on a new line. Also see :comment. Use "\n" to start a new line. Use "\r" to move the cursor to the first column. Uses the highlighting set by the :echohl command. Cannot be followed by a comment. Example:

:echo "the value of 'shell' is" &shell

:echo-redraw
A later redraw may make the message disappear again. And since Vim mostly postpones redrawing until it's finished with a sequence of commands this happens quite often. To avoid that a command from before the :echo causes a redraw afterwards (redraws are often postponed until you type something), force a redraw with the :redraw command. Example:

:new | redraw | echo "there is a new window"

:echo-self-refer
When printing nested containers echo prints second occurrence of the self-referencing container using "[...@level]" (self-referencing List) or "{...@level}" (self-referencing Dict):

:let l = []
:call add(l, l)
:let l2 = []
:call add(l2, [l2])
:echo l l2

echoes "[[...@0]] [[[...@0]]]". Echoing "[l]" will echo "[[[...@1]]]" because l first occurs at second level.

:echon
:echon {expr1} .. Echoes each {expr1}, without anything added. Also see :comment. Uses the highlighting set by the :echohl command. Cannot be followed by a comment. Example:

:echon "the value of 'shell' is " &shell

Note the difference between using :echo, which is a Vim command, and :!echo, which is an external shell command:

:!echo %		--> filename

The arguments of ":!" are expanded, see :_%.

:!echo "%"		--> filename or "filename"

Like the previous example. Whether you see the double quotes or not depends on your 'shell'.

:echo %			--> nothing

The '%' is an illegal character in an expression.

:echo "%"		--> %

This just echoes the '%' character.

:echo expand("%")	--> filename

This calls the expand() function to expand the '%'.

:echoh :echohl :echoh[l] {name} Use the highlight group {name} for the following :echo, :echon and :echomsg commands. Also used for the input() prompt. Example:

:echohl WarningMsg | echo "Don't panic!" | echohl None

Don't forget to set the group back to "None", otherwise all following echo's will be highlighted.

:echom :echomsg :echom[sg] {expr1} .. Echo the expression(s) as a true message, saving the message in the message-history. Spaces are placed between the arguments as with the :echo command. But unprintable characters are displayed, not interpreted. The parsing works slightly different from :echo, more like :execute. All the expressions are first evaluated and concatenated before echoing anything. If expressions does not evaluate to a Number or String, string() is used to turn it into a string. Uses the highlighting set by the :echohl command. Example:

:echomsg "It's a Zizzer Zazzer Zuzz, as you can plainly see."

See :echo-redraw to avoid the message disappearing when the screen is redrawn. :echoe :echoerr :echoe[rr] {expr1} .. Echo the expression(s) as an error message, saving the message in the message-history. When used in a script or function the line number will be added. Spaces are placed between the arguments as with the :echomsg command. When used inside a try conditional, the message is raised as an error exception instead (see try-echoerr). Example:

:echoerr "This script just failed!"

If you just want a highlighted message use :echohl. And to get a beep:

:exe "normal \<Esc>"

:eval
:eval {expr} Evaluate {expr} and discard the result. Example:

:eval Getlist()->Filter()->append('$')

The expression is supposed to have a side effect, since the resulting value is not used. In the example the append() call appends the List with text to the buffer. This is similar to :call but works with any expression.

The command can be shortened to :ev or :eva, but these are hard to recognize and therefore not to be used.

The command cannot be followed by "|" and another command, since "|" is seen as part of the expression.

:exe :execute :exe[cute] {expr1} .. Executes the string that results from the evaluation of {expr1} as an Ex command. Multiple arguments are concatenated, with a space in between. To avoid the extra space use the ".." operator to concatenate strings into one argument. {expr1} is used as the processed command, command line editing keys are not recognized. Cannot be followed by a comment. Examples:

:execute "buffer" nextbuf
:execute "normal" count .. "w"

":execute" can be used to append a command to commands that don't accept a '|'. Example:

:execute '!ls' | echo "theend"

":execute" is also a nice way to avoid having to type control characters in a Vim script for a ":normal" command:

:execute "normal ixxx\<Esc>"

This has an <Esc> character, see expr-string.

Be careful to correctly escape special characters in file names. The fnameescape() function can be used for Vim commands, shellescape() for :! commands. Examples:

:execute "e " .. fnameescape(filename)
:execute "!ls " .. shellescape(filename, 1)

Note: The executed string may be any command-line, but starting or ending "if", "while" and "for" does not always work, because when commands are skipped the ":execute" is not evaluated and Vim loses track of where blocks start and end. Also "break" and "continue" should not be inside ":execute". This example does not work, because the ":execute" is not evaluated and Vim does not see the "while", and gives an error for finding an ":endwhile":

:if 0
: execute 'while i > 5'
:  echo "test"
: endwhile
:endif

It is allowed to have a "while" or "if" command completely in the executed string:

:execute 'while i < 5 | echo i | let i = i + 1 | endwhile'

:exe-comment
":execute", ":echo" and ":echon" cannot be followed by a comment directly, because they see the '"' as the start of a string. But, you can use '|' followed by a comment. Example:

:echo "foo" | "this is a comment

8. Exception handling exception-handling

The Vim script language comprises an exception handling feature. This section explains how it can be used in a Vim script.

Exceptions may be raised by Vim on an error or on interrupt, see catch-errors and catch-interrupt. You can also explicitly throw an exception by using the ":throw" command, see throw-catch.

TRY CONDITIONALS try-conditionals

Exceptions can be caught or can cause cleanup code to be executed. You can use a try conditional to specify catch clauses (that catch exceptions) and/or a finally clause (to be executed for cleanup). A try conditional begins with a :try command and ends at the matching :endtry command. In between, you can use a :catch command to start a catch clause, or a :finally command to start a finally clause. There may be none or multiple catch clauses, but there is at most one finally clause, which must not be followed by any catch clauses. The lines before the catch clauses and the finally clause is called a try block.

:try
:	...
:	...				TRY BLOCK
:	...
:catch /{pattern}/
:	...
:	...				CATCH CLAUSE
:	...
:catch /{pattern}/
:	...
:	...				CATCH CLAUSE
:	...
:finally
:	...
:	...				FINALLY CLAUSE
:	...
:endtry

The try conditional allows to watch code for exceptions and to take the appropriate actions. Exceptions from the try block may be caught. Exceptions from the try block and also the catch clauses may cause cleanup actions. When no exception is thrown during execution of the try block, the control is transferred to the finally clause, if present. After its execution, the script continues with the line following the ":endtry". When an exception occurs during execution of the try block, the remaining lines in the try block are skipped. The exception is matched against the patterns specified as arguments to the ":catch" commands. The catch clause after the first matching ":catch" is taken, other catch clauses are not executed. The catch clause ends when the next ":catch", ":finally", or ":endtry" command is reached - whatever is first. Then, the finally clause (if present) is executed. When the ":endtry" is reached, the script execution continues in the following line as usual. When an exception that does not match any of the patterns specified by the ":catch" commands is thrown in the try block, the exception is not caught by that try conditional and none of the catch clauses is executed. Only the finally clause, if present, is taken. The exception pends during execution of the finally clause. It is resumed at the ":endtry", so that commands after the ":endtry" are not executed and the exception might be caught elsewhere, see try-nesting. When during execution of a catch clause another exception is thrown, the remaining lines in that catch clause are not executed. The new exception is not matched against the patterns in any of the ":catch" commands of the same try conditional and none of its catch clauses is taken. If there is, however, a finally clause, it is executed, and the exception pends during its execution. The commands following the ":endtry" are not executed. The new exception might, however, be caught elsewhere, see try-nesting. When during execution of the finally clause (if present) an exception is thrown, the remaining lines in the finally clause are skipped. If the finally clause has been taken because of an exception from the try block or one of the catch clauses, the original (pending) exception is discarded. The commands following the ":endtry" are not executed, and the exception from the finally clause is propagated and can be caught elsewhere, see try-nesting.

The finally clause is also executed, when a ":break" or ":continue" for a ":while" loop enclosing the complete try conditional is executed from the try block or a catch clause. Or when a ":return" or ":finish" is executed from the try block or a catch clause of a try conditional in a function or sourced script, respectively. The ":break", ":continue", ":return", or ":finish" pends during execution of the finally clause and is resumed when the ":endtry" is reached. It is, however, discarded when an exception is thrown from the finally clause. When a ":break" or ":continue" for a ":while" loop enclosing the complete try conditional or when a ":return" or ":finish" is encountered in the finally clause, the rest of the finally clause is skipped, and the ":break", ":continue", ":return" or ":finish" is executed as usual. If the finally clause has been taken because of an exception or an earlier ":break", ":continue", ":return", or ":finish" from the try block or a catch clause, this pending exception or command is discarded.

For examples see throw-catch and try-finally.

NESTING OF TRY CONDITIONALS try-nesting

Try conditionals can be nested arbitrarily. That is, a complete try conditional can be put into the try block, a catch clause, or the finally clause of another try conditional. If the inner try conditional does not catch an exception thrown in its try block or throws a new exception from one of its catch clauses or its finally clause, the outer try conditional is checked according to the rules above. If the inner try conditional is in the try block of the outer try conditional, its catch clauses are checked, but otherwise only the finally clause is executed. It does not matter for nesting, whether the inner try conditional is directly contained in the outer one, or whether the outer one sources a script or calls a function containing the inner try conditional.

When none of the active try conditionals catches an exception, just their finally clauses are executed. Thereafter, the script processing terminates. An error message is displayed in case of an uncaught exception explicitly thrown by a ":throw" command. For uncaught error and interrupt exceptions implicitly raised by Vim, the error message(s) or interrupt message are shown as usual.

For examples see throw-catch.

EXAMINING EXCEPTION HANDLING CODE except-examine

Exception handling code can get tricky. If you are in doubt what happens, set 'verbose' to 13 or use the ":13verbose" command modifier when sourcing your script file. Then you see when an exception is thrown, discarded, caught, or finished. When using a verbosity level of at least 14, things pending in a finally clause are also shown. This information is also given in debug mode (see debug-scripts).

THROWING AND CATCHING EXCEPTIONS throw-catch

You can throw any number or string as an exception. Use the :throw command and pass the value to be thrown as argument:

:throw 4711
:throw "string"

throw-expression
You can also specify an expression argument. The expression is then evaluated first, and the result is thrown:

:throw 4705 + strlen("string")
:throw strpart("strings", 0, 6)

An exception might be thrown during evaluation of the argument of the ":throw" command. Unless it is caught there, the expression evaluation is abandoned. The ":throw" command then does not throw a new exception. Example:

:function! Foo(arg)
:  try
:    throw a:arg
:  catch /foo/
:  endtry
:  return 1
:endfunction
:
:function! Bar()
:  echo "in Bar"
:  return 4710
:endfunction
:
:throw Foo("arrgh") + Bar()

This throws "arrgh", and "in Bar" is not displayed since Bar() is not executed.

:throw Foo("foo") + Bar()

however displays "in Bar" and throws 4711.

Any other command that takes an expression as argument might also be abandoned by an (uncaught) exception during the expression evaluation. The exception is then propagated to the caller of the command. Example:

:if Foo("arrgh")
:  echo "then"
:else
:  echo "else"
:endif

Here neither of "then" or "else" is displayed.

catch-order
Exceptions can be caught by a try conditional with one or more :catch commands, see try-conditionals. The values to be caught by each ":catch" command can be specified as a pattern argument. The subsequent catch clause gets executed when a matching exception is caught. Example:

:function! Foo(value)
:  try
:    throw a:value
:  catch /^\d\+$/
:    echo "Number thrown"
:  catch /.*/
:    echo "String thrown"
:  endtry
:endfunction
:
:call Foo(0x1267)
:call Foo('string')

The first call to Foo() displays "Number thrown", the second "String thrown". An exception is matched against the ":catch" commands in the order they are specified. Only the first match counts. So you should place the more specific ":catch" first. The following order does not make sense:

:  catch /.*/
:    echo "String thrown"
:  catch /^\d\+$/
:    echo "Number thrown"

The first ":catch" here matches always, so that the second catch clause is never taken.

throw-variables
If you catch an exception by a general pattern, you may access the exact value in the variable v:exception:

:  catch /^\d\+$/
:    echo "Number thrown.  Value is" v:exception

You may also be interested where an exception was thrown. This is stored in v:throwpoint. And you can obtain the stack trace from v:stacktrace. Note that "v:exception", "v:stacktrace" and "v:throwpoint" are valid for the exception most recently caught as long it is not finished. Example:

:function! Caught()
:  if v:exception != ""
:    echo 'Caught "' .. v:exception .. '" in ' .. v:throwpoint
:  else
:    echo 'Nothing caught'
:  endif
:endfunction
:
:function! Foo()
:  try
:    try
:      try
:	 throw 4711
:      finally
:	 call Caught()
:      endtry
:    catch /.*/
:      call Caught()
:      throw "oops"
:    endtry
:  catch /.*/
:    call Caught()
:  finally
:    call Caught()
:  endtry
:endfunction
:
:call Foo()

This displays

Nothing caught
Caught "4711" in function Foo, line 4
Caught "oops" in function Foo, line 10
Nothing caught

A practical example: The following command ":LineNumber" displays the line number in the script or function where it has been used:

:function! LineNumber()
:    return substitute(v:throwpoint, '.*\D\(\d\+\).*', '\1', "")
:endfunction
:command! LineNumber try | throw "" | catch | echo LineNumber() | endtry

try-nested
An exception that is not caught by a try conditional can be caught by a surrounding try conditional:

:try
:  try
:    throw "foo"
:  catch /foobar/
:    echo "foobar"
:  finally
:    echo "inner finally"
:  endtry
:catch /foo/
:  echo "foo"
:endtry

The inner try conditional does not catch the exception, just its finally clause is executed. The exception is then caught by the outer try conditional. The example displays "inner finally" and then "foo".

throw-from-catch
You can catch an exception and throw a new one to be caught elsewhere from the catch clause:

:function! Foo()
:  throw "foo"
:endfunction
:
:function! Bar()
:  try
:    call Foo()
:  catch /foo/
:    echo "Caught foo, throw bar"
:    throw "bar"
:  endtry
:endfunction
:
:try
:  call Bar()
:catch /.*/
:  echo "Caught" v:exception
:endtry

This displays "Caught foo, throw bar" and then "Caught bar".

rethrow
There is no real rethrow in the Vim script language, but you may throw "v:exception" instead:

:function! Bar()
:  try
:    call Foo()
:  catch /.*/
:    echo "Rethrow" v:exception
:    throw v:exception
:  endtry
:endfunction

try-echoerr
Note that this method cannot be used to "rethrow" Vim error or interrupt exceptions, because it is not possible to fake Vim internal exceptions. Trying so causes an error exception. You should throw your own exception denoting the situation. If you want to cause a Vim error exception containing the original error exception value, you can use the :echoerr command:

:try
:  try
:    asdf
:  catch /.*/
:    echoerr v:exception
:  endtry
:catch /.*/
:  echo v:exception
:endtry

This code displays

Vim(echoerr):Vim:E492: Not an editor command: asdf

CLEANUP CODE try-finally

Scripts often change global settings and restore them at their end. If the user however interrupts the script by pressing CTRL-C, the settings remain in an inconsistent state. The same may happen to you in the development phase of a script when an error occurs or you explicitly throw an exception without catching it. You can solve these problems by using a try conditional with a finally clause for restoring the settings. Its execution is guaranteed on normal control flow, on error, on an explicit ":throw", and on interrupt. (Note that errors and interrupts from inside the try conditional are converted to exceptions. When not caught, they terminate the script after the finally clause has been executed.) Example:

:try
:  let s:saved_ts = &ts
:  set ts=17
:
:  " Do the hard work here.
:
:finally
:  let &ts = s:saved_ts
:  unlet s:saved_ts
:endtry

This method should be used locally whenever a function or part of a script changes global settings which need to be restored on failure or normal exit of that function or script part.

break-finally
Cleanup code works also when the try block or a catch clause is left by a ":continue", ":break", ":return", or ":finish". Example:

:let first = 1
:while 1
:  try
:    if first
:      echo "first"
:      let first = 0
:      continue
:    else
:      throw "second"
:    endif
:  catch /.*/
:    echo v:exception
:    break
:  finally
:    echo "cleanup"
:  endtry
:  echo "still in while"
:endwhile
:echo "end"

This displays "first", "cleanup", "second", "cleanup", and "end".

:function! Foo()
:  try
:    return 4711
:  finally
:    echo "cleanup\n"
:  endtry
:  echo "Foo still active"
:endfunction
:
:echo Foo() "returned by Foo"

This displays "cleanup" and "4711 returned by Foo". You don't need to add an extra ":return" in the finally clause. (Above all, this would override the return value.)

except-from-finally
Using either of ":continue", ":break", ":return", ":finish", or ":throw" in a finally clause is possible, but not recommended since it abandons the cleanup actions for the try conditional. But, of course, interrupt and error exceptions might get raised from a finally clause. Example where an error in the finally clause stops an interrupt from working correctly:

:try
:  try
:    echo "Press CTRL-C for interrupt"
:    while 1
:    endwhile
:  finally
:    unlet novar
:  endtry
:catch /novar/
:endtry
:echo "Script still running"
:sleep 1

If you need to put commands that could fail into a finally clause, you should think about catching or ignoring the errors in these commands, see catch-errors and ignore-errors.

CATCHING ERRORS catch-errors

If you want to catch specific errors, you just have to put the code to be watched in a try block and add a catch clause for the error message. The presence of the try conditional causes all errors to be converted to an exception. No message is displayed and v:errmsg is not set then. To find the right pattern for the ":catch" command, you have to know how the format of the error exception is. Error exceptions have the following format:

Vim({cmdname}):{errmsg}

Vim:{errmsg}

{cmdname} is the name of the command that failed; the second form is used when the command name is not known. {errmsg} is the error message usually produced when the error occurs outside try conditionals. It always begins with a capital "E", followed by a two or three-digit error number, a colon, and a space.

Examples:

The command

:unlet novar

normally produces the error message

E108: No such variable: "novar"

which is converted inside try conditionals to an exception

Vim(unlet):E108: No such variable: "novar"

The command

:dwim

normally produces the error message

E492: Not an editor command: dwim

which is converted inside try conditionals to an exception

Vim:E492: Not an editor command: dwim

You can catch all ":unlet" errors by a

:catch /^Vim(unlet):/

or all errors for misspelled command names by a

:catch /^Vim:E492:/

Some error messages may be produced by different commands:

:function nofunc

and

:delfunction nofunc

both produce the error message

E128: Function name must start with a capital: nofunc

which is converted inside try conditionals to an exception

Vim(function):E128: Function name must start with a capital: nofunc

Vim(delfunction):E128: Function name must start with a capital: nofunc

respectively. You can catch the error by its number independently on the command that caused it if you use the following pattern:

:catch /^Vim(\a\+):E128:/

Some commands like

:let x = novar

produce multiple error messages, here:

E121: Undefined variable: novar
E15: Invalid expression:  novar

Only the first is used for the exception value, since it is the most specific one (see except-several-errors). So you can catch it by

:catch /^Vim(\a\+):E121:/

You can catch all errors related to the name "nofunc" by

:catch /\<nofunc\>/

You can catch all Vim errors in the ":write" and ":read" commands by

:catch /^Vim(\(write\|read\)):E\d\+:/

You can catch all Vim errors by the pattern

:catch /^Vim\((\a\+)\)\=:E\d\+:/

catch-text
NOTE: You should never catch the error message text itself:

:catch /No such variable/

only works in the English locale, but not when the user has selected a different language by the :language command. It is however helpful to cite the message text in a comment:

:catch /^Vim(\a\+):E108:/   " No such variable

IGNORING ERRORS ignore-errors

You can ignore errors in a specific Vim command by catching them locally:

:try
:  write
:catch
:endtry

But you are strongly recommended NOT to use this simple form, since it could catch more than you want. With the ":write" command, some autocommands could be executed and cause errors not related to writing, for instance:

:au BufWritePre * unlet novar

There could even be such errors you are not responsible for as a script writer: a user of your script might have defined such autocommands. You would then hide the error from the user. It is much better to use

:try
:  write
:catch /^Vim(write):/
:endtry

which only catches real write errors. So catch only what you'd like to ignore intentionally.

For a single command that does not cause execution of autocommands, you could even suppress the conversion of errors to exceptions by the ":silent!" command:

:silent! nunmap k

This works also when a try conditional is active.

CATCHING INTERRUPTS catch-interrupt

When there are active try conditionals, an interrupt (CTRL-C) is converted to the exception "Vim:Interrupt". You can catch it like every exception. The script is not terminated, then. Example:

:function! TASK1()
:  sleep 10
:endfunction
:function! TASK2()
:  sleep 20
:endfunction
:while 1
:  let command = input("Type a command: ")
:  try
:    if command == ""
:      continue
:    elseif command == "END"
:      break
:    elseif command == "TASK1"
:      call TASK1()
:    elseif command == "TASK2"
:      call TASK2()
:    else
:      echo "\nIllegal command:" command
:      continue
:    endif
:  catch /^Vim:Interrupt$/
:    echo "\nCommand interrupted"
:    " Caught the interrupt.  Continue with next prompt.
:  endtry
:endwhile

You can interrupt a task here by pressing CTRL-C; the script then asks for a new command. If you press CTRL-C at the prompt, the script is terminated.

For testing what happens when CTRL-C would be pressed on a specific line in your script, use the debug mode and execute the >quit or >interrupt command on that line. See debug-scripts.

CATCHING ALL catch-all

The commands

:catch /.*/
:catch //
:catch

catch everything, error exceptions, interrupt exceptions and exceptions explicitly thrown by the :throw command. This is useful at the top level of a script in order to catch unexpected things. Example:

:try
:
:  " do the hard work here
:
:catch /MyException/
:
:  " handle known problem
:
:catch /^Vim:Interrupt$/
:    echo "Script interrupted"
:catch /.*/
:  echo "Internal error (" .. v:exception .. ")"
:  echo " - occurred at " .. v:throwpoint
:endtry
:" end of script

Note: Catching all might catch more things than you want. Thus, you are strongly encouraged to catch only for problems that you can really handle by specifying a pattern argument to the ":catch". Example: Catching all could make it nearly impossible to interrupt a script by pressing CTRL-C:

:while 1
:  try
:    sleep 1
:  catch
:  endtry
:endwhile

EXCEPTIONS AND AUTOCOMMANDS except-autocmd

Exceptions may be used during execution of autocommands. Example:

:autocmd User x try
:autocmd User x   throw "Oops!"
:autocmd User x catch
:autocmd User x   echo v:exception
:autocmd User x endtry
:autocmd User x throw "Arrgh!"
:autocmd User x echo "Should not be displayed"
:
:try
:  doautocmd User x
:catch
:  echo v:exception
:endtry

This displays "Oops!" and "Arrgh!".

except-autocmd-Pre
For some commands, autocommands get executed before the main action of the command takes place. If an exception is thrown and not caught in the sequence of autocommands, the sequence and the command that caused its execution are abandoned and the exception is propagated to the caller of the command. Example:

:autocmd BufWritePre * throw "FAIL"
:autocmd BufWritePre * echo "Should not be displayed"
:
:try
:  write
:catch
:  echo "Caught:" v:exception "from" v:throwpoint
:endtry

Here, the ":write" command does not write the file currently being edited (as you can see by checking 'modified'), since the exception from the BufWritePre autocommand abandons the ":write". The exception is then caught and the script displays:

Caught: FAIL from BufWrite Auto commands for "*"

except-autocmd-Post
For some commands, autocommands get executed after the main action of the command has taken place. If this main action fails and the command is inside an active try conditional, the autocommands are skipped and an error exception is thrown that can be caught by the caller of the command. Example:

:autocmd BufWritePost * echo "File successfully written!"
:
:try
:  write /i/m/p/o/s/s/i/b/l/e
:catch
:  echo v:exception
:endtry

This just displays:

Vim(write):E212: Can't open file for writing (/i/m/p/o/s/s/i/b/l/e)

If you really need to execute the autocommands even when the main action fails, trigger the event from the catch clause. Example:

:autocmd BufWritePre  * set noreadonly
:autocmd BufWritePost * set readonly
:
:try
:  write /i/m/p/o/s/s/i/b/l/e
:catch
:  doautocmd BufWritePost /i/m/p/o/s/s/i/b/l/e
:endtry

You can also use ":silent!":

:let x = "ok"
:let v:errmsg = ""
:autocmd BufWritePost * if v:errmsg != ""
:autocmd BufWritePost *   let x = "after fail"
:autocmd BufWritePost * endif
:try
:  silent! write /i/m/p/o/s/s/i/b/l/e
:catch
:endtry
:echo x

This displays "after fail".

If the main action of the command does not fail, exceptions from the autocommands will be catchable by the caller of the command:

:autocmd BufWritePost * throw ":-("
:autocmd BufWritePost * echo "Should not be displayed"
:
:try
:  write
:catch
:  echo v:exception
:endtry

except-autocmd-Cmd
For some commands, the normal action can be replaced by a sequence of autocommands. Exceptions from that sequence will be catchable by the caller of the command. Example: For the ":write" command, the caller cannot know whether the file had actually been written when the exception occurred. You need to tell it in some way.

:if !exists("cnt")
:  let cnt = 0
:
:  autocmd BufWriteCmd * if &modified
:  autocmd BufWriteCmd *   let cnt = cnt + 1
:  autocmd BufWriteCmd *   if cnt % 3 == 2
:  autocmd BufWriteCmd *     throw "BufWriteCmdError"
:  autocmd BufWriteCmd *   endif
:  autocmd BufWriteCmd *   write | set nomodified
:  autocmd BufWriteCmd *   if cnt % 3 == 0
:  autocmd BufWriteCmd *     throw "BufWriteCmdError"
:  autocmd BufWriteCmd *   endif
:  autocmd BufWriteCmd *   echo "File successfully written!"
:  autocmd BufWriteCmd * endif
:endif
:
:try
:	write
:catch /^BufWriteCmdError$/
:  if &modified
:    echo "Error on writing (file contents not changed)"
:  else
:    echo "Error after writing"
:  endif
:catch /^Vim(write):/
:    echo "Error on writing"
:endtry

When this script is sourced several times after making changes, it displays first

File successfully written!

then

Error on writing (file contents not changed)

then

Error after writing

etc.

except-autocmd-ill
You cannot spread a try conditional over autocommands for different events. The following code is ill-formed:

:autocmd BufWritePre  * try
:
:autocmd BufWritePost * catch
:autocmd BufWritePost *   echo v:exception
:autocmd BufWritePost * endtry
:
:write

EXCEPTION HIERARCHIES AND PARAMETERIZED EXCEPTIONS except-hier-param

Some programming languages allow to use hierarchies of exception classes or to pass additional information with the object of an exception class. You can do similar things in Vim. In order to throw an exception from a hierarchy, just throw the complete class name with the components separated by a colon, for instance throw the string "EXCEPT:MATHERR:OVERFLOW" for an overflow in a mathematical library. When you want to pass additional information with your exception class, add it in parentheses, for instance throw the string "EXCEPT:IO:WRITEERR(myfile)" for an error when writing "myfile". With the appropriate patterns in the ":catch" command, you can catch for base classes or derived classes of your hierarchy. Additional information in parentheses can be cut out from v:exception with the ":substitute" command. Example:

:function! CheckRange(a, func)
:  if a:a < 0
:    throw "EXCEPT:MATHERR:RANGE(" .. a:func .. ")"
:  endif
:endfunction
:
:function! Add(a, b)
:  call CheckRange(a:a, "Add")
:  call CheckRange(a:b, "Add")
:  let c = a:a + a:b
:  if c < 0
:    throw "EXCEPT:MATHERR:OVERFLOW"
:  endif
:  return c
:endfunction
:
:function! Div(a, b)
:  call CheckRange(a:a, "Div")
:  call CheckRange(a:b, "Div")
:  if (a:b == 0)
:    throw "EXCEPT:MATHERR:ZERODIV"
:  endif
:  return a:a / a:b
:endfunction
:
:function! Write(file)
:  try
:    execute "write" fnameescape(a:file)
:  catch /^Vim(write):/
:    throw "EXCEPT:IO(" .. getcwd() .. ", " .. a:file .. "):WRITEERR"
:  endtry
:endfunction
:
:try
:
:  " something with arithmetic and I/O
:
:catch /^EXCEPT:MATHERR:RANGE/
:  let function = substitute(v:exception, '.*(\(\a\+\)).*', '\1', "")
:  echo "Range error in" function
:
:catch /^EXCEPT:MATHERR/	" catches OVERFLOW and ZERODIV
:  echo "Math error"
:
:catch /^EXCEPT:IO/
:  let dir = substitute(v:exception, '.*(\(.\+\),\s*.\+).*', '\1', "")
:  let file = substitute(v:exception, '.*(.\+,\s*\(.\+\)).*', '\1', "")
:  if file !~ '^/'
:    let file = dir .. "/" .. file
:  endif
:  echo 'I/O error for "' .. file .. '"'
:
:catch /^EXCEPT/
:  echo "Unspecified error"
:
:endtry

The exceptions raised by Vim itself (on error or when pressing CTRL-C) use a flat hierarchy: they are all in the "Vim" class. You cannot throw yourself exceptions with the "Vim" prefix; they are reserved for Vim. Vim error exceptions are parameterized with the name of the command that failed, if known. See catch-errors.

PECULIARITIES

except-compat
The exception handling concept requires that the command sequence causing the exception is aborted immediately and control is transferred to finally clauses and/or a catch clause.

In the Vim script language there are cases where scripts and functions continue after an error: in functions without the "abort" flag or in a command after ":silent!", control flow goes to the following line, and outside functions, control flow goes to the line following the outermost ":endwhile" or ":endif". On the other hand, errors should be catchable as exceptions (thus, requiring the immediate abortion).

This problem has been solved by converting errors to exceptions and using immediate abortion (if not suppressed by ":silent!") only when a try conditional is active. This is no restriction since an (error) exception can be caught only from an active try conditional. If you want an immediate termination without catching the error, just use a try conditional without catch clause. (You can cause cleanup code being executed before termination by specifying a finally clause.)

When no try conditional is active, the usual abortion and continuation behavior is used instead of immediate abortion. This ensures compatibility of scripts written for Vim 6.1 and earlier.

However, when sourcing an existing script that does not use exception handling commands (or when calling one of its functions) from inside an active try conditional of a new script, you might change the control flow of the existing script on error. You get the immediate abortion on error and can catch the error in the new script. If however the sourced script suppresses error messages by using the ":silent!" command (checking for errors by testing v:errmsg if appropriate), its execution path is not changed. The error is not converted to an exception. (See :silent.) So the only remaining cause where this happens is for scripts that don't care about errors and produce error messages. You probably won't want to use such code from your new scripts.

except-syntax-err
Syntax errors in the exception handling commands are never caught by any of the ":catch" commands of the try conditional they belong to. Its finally clauses, however, is executed. Example:

:try
:  try
:    throw 4711
:  catch /\(/
:    echo "in catch with syntax error"
:  catch
:    echo "inner catch-all"
:  finally
:    echo "inner finally"
:  endtry
:catch
:  echo 'outer catch-all caught "' .. v:exception .. '"'
:  finally
:    echo "outer finally"
:endtry

This displays:

inner finally
outer catch-all caught "Vim(catch):E54: Unmatched \("
outer finally

The original exception is discarded and an error exception is raised, instead.

except-single-line
The ":try", ":catch", ":finally", and ":endtry" commands can be put on a single line, but then syntax errors may make it difficult to recognize the "catch" line, thus you better avoid this. Example:

:try | unlet! foo # | catch | endtry

raises an error exception for the trailing characters after the ":unlet!" argument, but does not see the ":catch" and ":endtry" commands, so that the error exception is discarded and the "E488: Trailing characters" message gets displayed.

except-several-errors
When several errors appear in a single command, the first error message is usually the most specific one and therefore converted to the error exception. Example:

echo novar

causes

E121: Undefined variable: novar
E15: Invalid expression: novar

The value of the error exception inside try conditionals is:

Vim(echo):E121: Undefined variable: novar

except-syntax-error
But when a syntax error is detected after a normal error in the same command, the syntax error is used for the exception being thrown. Example:

unlet novar #

causes

E108: No such variable: "novar"
E488: Trailing characters

The value of the error exception inside try conditionals is:

Vim(unlet):E488: Trailing characters

This is done because the syntax error might change the execution path in a way not intended by the user. Example:

try
    try | unlet novar # | catch | echo v:exception | endtry
catch /.*/
    echo "outer catch:" v:exception
endtry

This displays "outer catch: Vim(unlet):E488: Trailing characters", and then a "E600: Missing :endtry" error message is given, see except-single-line.

9. Examples eval-examples

Printing in Binary

:" The function Nr2Bin() returns the binary string representation of a number.
:func Nr2Bin(nr)
:  let n = a:nr
:  let r = ""
:  while n
:    let r = '01'[n % 2] .. r
:    let n = n / 2
:  endwhile
:  return r
:endfunc
:" The function String2Bin() converts each character in a string to a
:" binary string, separated with dashes.
:func String2Bin(str)
:  let out = ''
:  for ix in range(strlen(a:str))
:    let out = out .. '-' .. Nr2Bin(char2nr(a:str[ix]))
:  endfor
:  return out[1:]
:endfunc

Example of its use:

:echo Nr2Bin(32)

result: "100000"

:echo String2Bin("32")

result: "110011-110010"

Sorting lines

This example sorts lines with a specific compare function.

:func SortBuffer()
:  let lines = getline(1, '$')
:  call sort(lines, function("Strcmp"))
:  call setline(1, lines)
:endfunction

As a one-liner:

:call setline(1, sort(getline(1, '$'), function("Strcmp")))

scanf() replacement

sscanf
There is no sscanf() function in Vim. If you need to extract parts from a line, you can use matchstr() and substitute() to do it. This example shows how to get the file name, line number and column number out of a line like "foobar.txt, 123, 45".

:" Set up the match bit
:let mx='\(\f\+\),\s*\(\d\+\),\s*\(\d\+\)'
:"get the part matching the whole expression
:let l = matchstr(line, mx)
:"get each item out of the match
:let file = substitute(l, mx, '\1', '')
:let lnum = substitute(l, mx, '\2', '')
:let col = substitute(l, mx, '\3', '')

The input is in the variable "line", the results in the variables "file", "lnum" and "col". (idea from Michael Geddes)

getting the scriptnames in a Dictionary

scriptnames-dictionary
The :scriptnames command can be used to get a list of all script files that have been sourced. There is also the getscriptinfo() function, but the information returned is not exactly the same. In case you need to manipulate the output of scriptnames this code can be used:

" Get the output of ":scriptnames" in the scriptnames_output variable.
let scriptnames_output = ''
redir => scriptnames_output
silent scriptnames
redir END
" Split the output into lines and parse each line.	Add an entry to the
" "scripts" dictionary.
let scripts = {}
for line in split(scriptnames_output, "\n")
  " Only do non-blank lines.
  if line =~ '\S'
    " Get the first number in the line.
    let nr = matchstr(line, '\d\+')
    " Get the file name, remove the script number " 123: ".
    let name = substitute(line, '.\+:\s*', '', '')
    " Add an item to the Dictionary
    let scripts[nr] = name
  endif
endfor
unlet scriptnames_output

The sandbox eval-sandbox sandbox

The 'foldexpr', 'formatexpr', 'includeexpr', 'indentexpr', 'statusline' and 'foldtext' options may be evaluated in a sandbox. This means that you are protected from these expressions having nasty side effects. This gives some safety for when these options are set from a modeline. It is also used when the command from a tags file is executed and for CTRL-R = in the command line. The sandbox is also used for the :sandbox command.

E48
These items are not allowed in the sandbox:

changing the buffer text

defining or changing mapping, autocommands, user commands

setting certain options (see option-summary)

setting certain v: variables (see v:var) E794

executing a shell command

reading or writing a file

jumping to another buffer or editing a file

executing Python, Perl, etc. commands This is not guaranteed 100% secure, but it should block most attacks.

:san :sandbox :san[dbox] {cmd} Execute {cmd} in the sandbox. Useful to evaluate an option that may have been set from a modeline, e.g. 'foldexpr'.

sandbox-option
A few options contain an expression. When this expression is evaluated it may have to be done in the sandbox to avoid a security risk. But the sandbox is restrictive, thus this only happens when the option was set from an insecure location. Insecure in this context are:

sourcing a .nvimrc or .exrc in the current directory

while executing in the sandbox

value coming from a modeline

executing a function that was defined in the sandbox

Note that when in the sandbox and saving an option value and restoring it, the option will still be marked as it was set in the sandbox.

Textlock textlock

In a few situations it is not allowed to change the text in the buffer, jump to another window and some other things that might confuse or break what Vim is currently doing. This mostly applies to things that happen when Vim is actually doing something else. For example, a TextYankPost autocommand cannot edit the text it is yanking.

This is not allowed when the textlock is active:

changing the buffer text

jumping to another buffer or window

editing another file

closing a window or quitting Vim

etc.

Vim script library vim-script-library

Vim comes bundled with a Vim script library, that can be used by runtime, script authors. Currently, it only includes very few functions, but it may grow over time.

dist#vim
The functions make use of the autoloaded prefix "dist#vim".

The following functions are available:

dist#vim#IsSafeExecutable(filetype, executable)

This function takes a filetype and an executable and checks whether it is safe to execute the given executable. For security reasons users may not want to have Vim execute random executables or may have forbidden to do so for specific filetypes by setting the "<filetype>_exec" variable (plugin_exec).

It returns TRUE or FALSE to indicate whether the plugin should run the given executable. It takes the following arguments:

argument type

filetype string executable string

Command-line expressions highlighting expr-highlight

Expressions entered by the user in i_CTRL-R_=, c_CTRL-\_e, quote= are highlighted by the built-in expressions parser. It uses highlight groups described in the table below, which may be overridden by colorschemes. hl-NvimInvalid
Besides the "Nvim"-prefixed highlight groups described below, there are "NvimInvalid"-prefixed highlight groups which have the same meaning but indicate that the token contains an error or that an error occurred just before it. They have mostly the same hierarchy, except that (by default) in place of any non-Nvim-prefixed group NvimInvalid linking to Error is used and some other intermediate groups are present.

Group Default link Colored expression

hl-NvimInternalError None, red/red Parser bug

hl-NvimAssignment Operator Generic assignment hl-NvimPlainAssignment NvimAssignment = in :let hl-NvimAugmentedAssignment NvimAssignment Generic, +=/`-=`/`.=` hl-NvimAssignmentWithAddition NvimAugmentedAssignment += in :let+= hl-NvimAssignmentWithSubtraction NvimAugmentedAssignment -= in :let-= hl-NvimAssignmentWithConcatenation NvimAugmentedAssignment .= in :let.=

hl-NvimOperator Operator Generic operator

hl-NvimUnaryOperator NvimOperator Generic unary op hl-NvimUnaryPlus NvimUnaryOperator expr-unary-+ hl-NvimUnaryMinus NvimUnaryOperator expr-unary-- hl-NvimNot NvimUnaryOperator expr-!

hl-NvimBinaryOperator NvimOperator Generic binary op hl-NvimComparison NvimBinaryOperator Any expr4 operator hl-NvimComparisonModifier NvimComparison #/`?` near expr4 op hl-NvimBinaryPlus NvimBinaryOperator expr-+ hl-NvimBinaryMinus NvimBinaryOperator expr-- hl-NvimConcat NvimBinaryOperator expr-. hl-NvimConcatOrSubscript NvimConcat expr-. or expr-entry hl-NvimOr NvimBinaryOperator expr-barbar hl-NvimAnd NvimBinaryOperator expr-&& hl-NvimMultiplication NvimBinaryOperator expr-star hl-NvimDivision NvimBinaryOperator expr-/ hl-NvimMod NvimBinaryOperator expr-%

hl-NvimTernary NvimOperator ? in expr1 hl-NvimTernaryColon NvimTernary : in expr1

hl-NvimParenthesis Delimiter Generic bracket hl-NvimLambda NvimParenthesis {/`}` in lambda hl-NvimNestingParenthesis NvimParenthesis (/`)` in expr-nesting hl-NvimCallingParenthesis NvimParenthesis (/`)` in expr-function

hl-NvimSubscript NvimParenthesis Generic subscript hl-NvimSubscriptBracket NvimSubscript [/`]` in expr-[] hl-NvimSubscriptColon NvimSubscript : in expr-[:] hl-NvimCurly NvimSubscript {/`}` in curly-braces-names

hl-NvimContainer NvimParenthesis Generic container hl-NvimDict NvimContainer {/`}` in dict literal hl-NvimList NvimContainer [/`]` in list literal

hl-NvimIdentifier Identifier Generic identifier hl-NvimIdentifierScope NvimIdentifier Namespace: letter before : in internal-variables hl-NvimIdentifierScopeDelimiter NvimIdentifier : after namespace letter hl-NvimIdentifierName NvimIdentifier Rest of the ident hl-NvimIdentifierKey NvimIdentifier Identifier after expr-entry

hl-NvimColon Delimiter : in dict literal hl-NvimComma Delimiter , in dict or list literal or expr-function hl-NvimArrow Delimiter -> in lambda

hl-NvimRegister SpecialChar expr-register hl-NvimNumber Number Non-prefix digits in integer expr-number hl-NvimNumberPrefix Type 0 for octal-number 0x for hex-number 0b for binary-number hl-NvimFloat NvimNumber Floating-point number

hl-NvimOptionSigil Type & in expr-option hl-NvimOptionScope NvimIdentifierScope Option scope if any hl-NvimOptionScopeDelimiter NvimIdentifierScopeDelimiter : after option scope hl-NvimOptionName NvimIdentifier Option name

hl-NvimEnvironmentSigil NvimOptionSigil $ in expr-env hl-NvimEnvironmentName NvimIdentifier Env variable name

hl-NvimString String Generic string hl-NvimStringBody NvimString Generic string literal body hl-NvimStringQuote NvimString Generic string quote hl-NvimStringSpecial SpecialChar Generic string non-literal body

hl-NvimSingleQuote NvimStringQuote ' in expr-' hl-NvimSingleQuotedBody NvimStringBody Literal part of expr-' string body hl-NvimSingleQuotedQuote NvimStringSpecial '' inside expr-' string body

hl-NvimDoubleQuote NvimStringQuote " in expr-quote hl-NvimDoubleQuotedBody NvimStringBody Literal part of expr-quote body hl-NvimDoubleQuotedEscape NvimStringSpecial Valid expr-quote escape sequence hl-NvimDoubleQuotedUnknownEscape NvimInvalidValue Unrecognized expr-quote escape sequence