Editing other files

This chapter is about editing files that are not ordinary files. With Vim you can edit files that are compressed. Some files need to be accessed over the internet. With some restrictions, binary files can be edited as well.

23.1 DOS, Mac and Unix files 23.2 Files on the internet 23.3 Binary files 23.4 Compressed files

Next chapter: usr_24.txt Inserting quickly Previous chapter: usr_22.txt Finding the file to edit Table of contents: usr_toc.txt

Back in the early days, the old Teletype machines used two characters to start a new line. One to move the carriage back to the first position (carriage return, <CR>), another to move the paper up (line feed, <LF>). When computers came out, storage was expensive. Some people decided that they did not need two characters for end-of-line. The Unix people decided they could use <New Line> or <NL> only for end-of-line. The Apple people standardized on <CR>. The Microsoft Windows folks decided to keep the old <CR><NL> (we use <NL> for line feed in the help text). This means that if you try to move a file from one system to another, you have line-break problems. The Vim editor automatically recognizes the different file formats and handles things properly behind your back. The option 'fileformats' contains the various formats that will be tried when a new file is edited. The following command, for example, tells Vim to try Unix format first and MS-DOS format second:

:set fileformats=unix,dos

You will notice the format in the message you get when editing a file. You don't see anything if you edit a native file format. Thus editing a Unix file on Unix won't result in a remark. But when you edit a dos file, Vim will notify you of this:

For a Mac file you would see "[mac]". The detected file format is stored in the 'fileformat' option. To see which format you have, execute the following command:

:set fileformat?

The three names that Vim uses are:

unix <NL> dos <CR><NL> mac <CR>

On Unix, <NL> is used to break a line. It's not unusual to have a <CR> character halfway in a line. Incidentally, this happens quite often in Vi (and Vim) scripts. On the Macintosh, where <CR> is the line break character, it's possible to have a <NL> character halfway in a line. The result is that it's not possible to be 100% sure whether a file containing both <CR> and <NL> characters is a Mac or a Unix file. Therefore, Vim assumes that on Unix you probably won't edit a Mac file, and doesn't check for this type of file. To check for this format anyway, add "mac" to 'fileformats':

:set fileformats+=mac

Then Vim will take a guess at the file format. Watch out for situations where Vim guesses wrong.

If you use the good old Vi and try to edit an MS-DOS format file, you will find that each line ends with a ^M character. (^M is <CR>). The automatic detection avoids this. Suppose you do want to edit the file that way? Then you need to overrule the format:

:edit ++ff=unix file.txt

The "++" string is an item that tells Vim that an option name follows, which overrules the default for this single command. "++ff" is used for 'fileformat'. You could also use "++ff=mac" or "++ff=dos". This doesn't work for any option, only "++ff" and "++enc" are currently implemented. The full names "++fileformat" and "++encoding" also work.

You can use the 'fileformat' option to convert from one file format to another. Suppose, for example, that you have an MS-DOS file named README.TXT that you want to convert to Unix format. Start by editing the MS-DOS format file:

vim README.TXT

Vim will recognize this as a dos format file. Now change the file format to Unix:

:set fileformat=unix
:write

The file is written in Unix format.

Someone sends you an e-mail message, which refers to a file by its URL. For example:

https://ftp.nluug.nl/pub/vim/README

You could start a program to download the file, save it on your local disk and then start Vim to edit it. There is a much simpler way. Move the cursor to any character of the URL. Then use this command:

gf

With a bit of luck, Vim will figure out which program to use for downloading the file, download it and edit the copy. To open the file in a new window use CTRL-W f. If something goes wrong you will get an error message. It's possible that the URL is wrong, you don't have permission to read it, the network connection is down, etc. Unfortunately, it's hard to tell the cause of the error. You might want to try the manual way of downloading the file.

Accessing files over the internet works with the netrw plugin. Currently URLs with these formats are recognized:

ftp:// uses ftp rcp:// uses rcp scp:// uses scp http:// uses wget (reading only)

Vim doesn't do the communication itself, it relies on the mentioned programs to be available on your computer. On most Unix systems "ftp" and "rcp" will be present. "scp" and "wget" might need to be installed.

Vim detects these URLs for each command that starts editing a new file, also with ":edit" and ":split", for example. Write commands also work, except for http://.

For more information, also about passwords, see netrw.

You can edit binary files with Vim. Vim wasn't really made for this, thus there are a few restrictions. But you can read a file, change a character and write it back, with the result that only that one character was changed and the file is identical otherwise. To make sure that Vim does not use its clever tricks in the wrong way, add the "-b" argument when starting Vim:

vim -b datafile

This sets the 'binary' option. The effect of this is that unexpected side effects are turned off. For example, 'textwidth' is set to zero, to avoid automatic formatting of lines. And files are always read in Unix file format.

Binary mode can be used to change a message in a program. Be careful not to insert or delete any characters, it would stop the program from working. Use "R" to enter replace mode.

Many characters in the file will be unprintable. To see them in Hex format:

:set display=uhex

Otherwise, the "ga" command can be used to see the value of the character under the cursor. The output, when the cursor is on an <Esc>, looks like this:

There might not be many line breaks in the file. To get some overview switch the 'wrap' option off:

:set nowrap

BYTE POSITION

To see on which byte you are in the file use this command:

g CTRL-G

The output is verbose:

The last two numbers are the byte position in the file and the total number of bytes. This takes into account how 'fileformat' changes the number of bytes that a line break uses. To move to a specific byte in the file, use the "go" command. For example, to move to byte 2345:

2345go

USING XXD

A real binary editor shows the text in two ways: as it is and in hex format. You can do this in Vim by first converting the file with the "xxd" program. This comes with Vim. First edit the file in binary mode:

vim -b datafile

Now convert the file to a hex dump with xxd:

:%!xxd

The text will look like this:

0000000: 1f8b 0808 39d7 173b 0203 7474 002b 4e49  ....9..;..tt.+NI
0000010: 4b2c 8660 eb9c ecac c462 eb94 345e 2e30  K,.`.....b..4^.0
0000020: 373b 2731 0b22 0ca6 c1a2 d669 1035 39d9  7;'1.".....i.59.

You can now view and edit the text as you like. Vim treats the information as ordinary text. Changing the hex does not cause the printable character to be changed, or the other way around. Finally convert it back with:

:%!xxd -r

Only changes in the hex part are used. Changes in the printable text part on the right are ignored.

See the manual page of xxd for more information.

This is easy: You can edit a compressed file just like any other file. The "gzip" plugin takes care of decompressing the file when you edit it. And compressing it again when you write it. These compression methods are currently supported:

.Z compress .gz gzip .bz2 bzip2

Vim uses the mentioned programs to do the actual compression and decompression. You might need to install the programs first.

Next chapter: usr_24.txt Inserting quickly

Copyright: see manual-copyright