343 lines
12 KiB
Text
343 lines
12 KiB
Text
*usr_23.txt* For Vim version 7.4. Last change: 2006 Apr 24
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VIM USER MANUAL - by Bram Moolenaar
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Editing other files
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This chapter is about editing files that are not ordinary files. With Vim you
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can edit files that are compressed or encrypted. Some files need to be
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accessed over the internet. With some restrictions, binary files can be
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edited as well.
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|23.1| DOS, Mac and Unix files
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|23.2| Files on the internet
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|23.3| Encryption
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|23.4| Binary files
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|23.5| Compressed files
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Next chapter: |usr_24.txt| Inserting quickly
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Previous chapter: |usr_22.txt| Finding the file to edit
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Table of contents: |usr_toc.txt|
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==============================================================================
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*23.1* DOS, Mac and Unix files
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Back in the early days, the old Teletype machines used two characters to
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start a new line. One to move the carriage back to the first position
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(carriage return, <CR>), another to move the paper up (line feed, <LF>).
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When computers came out, storage was expensive. Some people decided that
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they did not need two characters for end-of-line. The UNIX people decided
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they could use <Line Feed> only for end-of-line. The Apple people
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standardized on <CR>. The MS-DOS (and Microsoft Windows) folks decided to
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keep the old <CR><LF>.
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This means that if you try to move a file from one system to another, you
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have line-break problems. The Vim editor automatically recognizes the
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different file formats and handles things properly behind your back.
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The option 'fileformats' contains the various formats that will be tried
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when a new file is edited. The following command, for example, tells Vim to
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try UNIX format first and MS-DOS format second: >
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:set fileformats=unix,dos
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You will notice the format in the message you get when editing a file. You
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don't see anything if you edit a native file format. Thus editing a Unix file
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on Unix won't result in a remark. But when you edit a dos file, Vim will
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notify you of this:
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"/tmp/test" [dos] 3L, 71C ~
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For a Mac file you would see "[mac]".
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The detected file format is stored in the 'fileformat' option. To see
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which format you have, execute the following command: >
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:set fileformat?
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The three names that Vim uses are:
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unix <LF>
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dos <CR><LF>
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mac <CR>
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USING THE MAC FORMAT
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On Unix, <LF> is used to break a line. It's not unusual to have a <CR>
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character halfway a line. Incidentally, this happens quite often in Vi (and
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Vim) scripts.
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On the Macintosh, where <CR> is the line break character, it's possible to
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have a <LF> character halfway a line.
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The result is that it's not possible to be 100% sure whether a file
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containing both <CR> and <LF> characters is a Mac or a Unix file. Therefore,
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Vim assumes that on Unix you probably won't edit a Mac file, and doesn't check
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for this type of file. To check for this format anyway, add "mac" to
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'fileformats': >
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:set fileformats+=mac
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Then Vim will take a guess at the file format. Watch out for situations where
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Vim guesses wrong.
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OVERRULING THE FORMAT
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If you use the good old Vi and try to edit an MS-DOS format file, you will
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find that each line ends with a ^M character. (^M is <CR>). The automatic
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detection avoids this. Suppose you do want to edit the file that way? Then
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you need to overrule the format: >
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:edit ++ff=unix file.txt
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The "++" string is an item that tells Vim that an option name follows, which
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overrules the default for this single command. "++ff" is used for
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'fileformat'. You could also use "++ff=mac" or "++ff=dos".
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This doesn't work for any option, only "++ff" and "++enc" are currently
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implemented. The full names "++fileformat" and "++encoding" also work.
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CONVERSION
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You can use the 'fileformat' option to convert from one file format to
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another. Suppose, for example, that you have an MS-DOS file named README.TXT
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that you want to convert to UNIX format. Start by editing the MS-DOS format
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file: >
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vim README.TXT
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Vim will recognize this as a dos format file. Now change the file format to
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UNIX: >
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:set fileformat=unix
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:write
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The file is written in Unix format.
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==============================================================================
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*23.2* Files on the internet
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Someone sends you an e-mail message, which refers to a file by its URL. For
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example:
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You can find the information here: ~
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ftp://ftp.vim.org/pub/vim/README ~
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You could start a program to download the file, save it on your local disk and
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then start Vim to edit it.
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There is a much simpler way. Move the cursor to any character of the URL.
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Then use this command: >
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gf
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With a bit of luck, Vim will figure out which program to use for downloading
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the file, download it and edit the copy. To open the file in a new window use
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CTRL-W f.
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If something goes wrong you will get an error message. It's possible that
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the URL is wrong, you don't have permission to read it, the network connection
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is down, etc. Unfortunately, it's hard to tell the cause of the error. You
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might want to try the manual way of downloading the file.
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Accessing files over the internet works with the netrw plugin. Currently URLs
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with these formats are recognized:
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ftp:// uses ftp
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rcp:// uses rcp
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scp:// uses scp
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http:// uses wget (reading only)
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Vim doesn't do the communication itself, it relies on the mentioned programs
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to be available on your computer. On most Unix systems "ftp" and "rcp" will
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be present. "scp" and "wget" might need to be installed.
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Vim detects these URLs for each command that starts editing a new file, also
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with ":edit" and ":split", for example. Write commands also work, except for
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http://.
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For more information, also about passwords, see |netrw|.
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==============================================================================
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*23.3* Encryption
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Some information you prefer to keep to yourself. For example, when writing
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a test on a computer that students also use. You don't want clever students
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to figure out a way to read the questions before the exam starts. Vim can
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encrypt the file for you, which gives you some protection.
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To start editing a new file with encryption, use the "-x" argument to start
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Vim. Example: >
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vim -x exam.txt
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Vim prompts you for a key used for encrypting and decrypting the file:
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Enter encryption key: ~
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Carefully type the secret key now. You cannot see the characters you type,
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they will be replaced by stars. To avoid the situation that a typing mistake
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will cause trouble, Vim asks you to enter the key again:
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Enter same key again: ~
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You can now edit this file normally and put in all your secrets. When you
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finish editing the file and tell Vim to exit, the file is encrypted and
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written.
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When you edit the file with Vim, it will ask you to enter the same key
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again. You don't need to use the "-x" argument. You can also use the normal
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":edit" command. Vim adds a magic string to the file by which it recognizes
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that the file was encrypted.
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If you try to view this file using another program, all you get is garbage.
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Also, if you edit the file with Vim and enter the wrong key, you get garbage.
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Vim does not have a mechanism to check if the key is the right one (this makes
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it much harder to break the key).
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SWITCHING ENCRYPTION ON AND OFF
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To disable the encryption of a file, set the 'key' option to an empty string:
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>
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:set key=
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The next time you write the file this will be done without encryption.
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Setting the 'key' option to enable encryption is not a good idea, because
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the password appears in the clear. Anyone shoulder-surfing can read your
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password.
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To avoid this problem, the ":X" command was created. It asks you for an
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encryption key, just like the "-x" argument did: >
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:X
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Enter encryption key: ******
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Enter same key again: ******
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LIMITS ON ENCRYPTION
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The encryption algorithm used by Vim is weak. It is good enough to keep out
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the casual prowler, but not good enough to keep out a cryptology expert with
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lots of time on his hands. Also you should be aware that the swap file is not
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encrypted; so while you are editing, people with superuser privileges can read
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the unencrypted text from this file.
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One way to avoid letting people read your swap file is to avoid using one.
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If the -n argument is supplied on the command line, no swap file is used
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(instead, Vim puts everything in memory). For example, to edit the encrypted
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file "file.txt" without a swap file use the following command: >
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vim -x -n file.txt
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When already editing a file, the swapfile can be disabled with: >
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:setlocal noswapfile
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Since there is no swapfile, recovery will be impossible. Save the file a bit
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more often to avoid the risk of losing your changes.
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While the file is in memory, it is in plain text. Anyone with privilege can
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look in the editor's memory and discover the contents of the file.
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If you use a viminfo file, be aware that the contents of text registers are
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written out in the clear as well.
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If you really want to secure the contents of a file, edit it only on a
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portable computer not connected to a network, use good encryption tools, and
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keep the computer locked up in a big safe when not in use.
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==============================================================================
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*23.4* Binary files
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You can edit binary files with Vim. Vim wasn't really made for this, thus
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there are a few restrictions. But you can read a file, change a character and
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write it back, with the result that only that one character was changed and
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the file is identical otherwise.
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To make sure that Vim does not use its clever tricks in the wrong way, add
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the "-b" argument when starting Vim: >
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vim -b datafile
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This sets the 'binary' option. The effect of this is that unexpected side
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effects are turned off. For example, 'textwidth' is set to zero, to avoid
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automatic formatting of lines. And files are always read in Unix file format.
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Binary mode can be used to change a message in a program. Be careful not to
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insert or delete any characters, it would stop the program from working. Use
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"R" to enter replace mode.
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Many characters in the file will be unprintable. To see them in Hex format: >
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:set display=uhex
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Otherwise, the "ga" command can be used to see the value of the character
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under the cursor. The output, when the cursor is on an <Esc>, looks like
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this:
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<^[> 27, Hex 1b, Octal 033 ~
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There might not be many line breaks in the file. To get some overview switch
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the 'wrap' option off: >
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:set nowrap
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BYTE POSITION
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To see on which byte you are in the file use this command: >
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g CTRL-G
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The output is verbose:
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Col 9-16 of 9-16; Line 277 of 330; Word 1806 of 2058; Byte 10580 of 12206 ~
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The last two numbers are the byte position in the file and the total number of
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bytes. This takes into account how 'fileformat' changes the number of bytes
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that a line break uses.
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To move to a specific byte in the file, use the "go" command. For
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example, to move to byte 2345: >
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2345go
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USING XXD
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A real binary editor shows the text in two ways: as it is and in hex format.
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You can do this in Vim by first converting the file with the "xxd" program.
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This comes with Vim.
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First edit the file in binary mode: >
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vim -b datafile
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Now convert the file to a hex dump with xxd: >
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:%!xxd
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The text will look like this:
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0000000: 1f8b 0808 39d7 173b 0203 7474 002b 4e49 ....9..;..tt.+NI ~
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0000010: 4b2c 8660 eb9c ecac c462 eb94 345e 2e30 K,.`.....b..4^.0 ~
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0000020: 373b 2731 0b22 0ca6 c1a2 d669 1035 39d9 7;'1.".....i.59. ~
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You can now view and edit the text as you like. Vim treats the information as
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ordinary text. Changing the hex does not cause the printable character to be
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changed, or the other way around.
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Finally convert it back with:
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>
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:%!xxd -r
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Only changes in the hex part are used. Changes in the printable text part on
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the right are ignored.
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See the manual page of xxd for more information.
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==============================================================================
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*23.5* Compressed files
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This is easy: You can edit a compressed file just like any other file. The
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"gzip" plugin takes care of decompressing the file when you edit it. And
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compressing it again when you write it.
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These compression methods are currently supported:
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.Z compress
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.gz gzip
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.bz2 bzip2
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Vim uses the mentioned programs to do the actual compression and
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decompression. You might need to install the programs first.
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==============================================================================
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Next chapter: |usr_24.txt| Inserting quickly
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Copyright: see |manual-copyright| vim:tw=78:ts=8:ft=help:norl:
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