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22.9 Specifying a Coding System for File Text

In cases where Emacs does not automatically choose the right coding system for a file’s contents, you can use these commands to specify one:

C-x RET f coding RET​

Use coding system coding to save or revisit the file in the current buffer (set-buffer-file-coding-system).

C-x RET c coding RET​

Specify coding system coding for the immediately following command (universal-coding-system-argument).

C-x RET r coding RET​

Revisit the current file using the coding system coding (revert-buffer-with-coding-system).

M-x recode-region RET right RET wrong RET​

Convert a region that was decoded using coding system wrong, decoding it using coding system right instead.

The command C-x RET f (set-buffer-file-coding-system) sets the file coding system for the current buffer (i.e., the coding system to use when saving or reverting the file). You specify which coding system using the minibuffer. You can also invoke this command by clicking with mouse-3 on the coding system indicator in the mode line (see Mode Line).

If you specify a coding system that cannot handle all the characters in the buffer, Emacs will warn you about the troublesome characters, and ask you to choose another coding system, when you try to save the buffer (see Output Coding).

You can also use this command to specify the end-of-line conversion (see end-of-line conversion) for encoding the current buffer. For example, C-x RET f dos RET will cause Emacs to save the current buffer’s text with DOS-style carriage return followed by linefeed line endings.

Another way to specify the coding system for a file is when you visit the file. First use the command C-x RET c (universal-coding-system-argument); this command uses the minibuffer to read a coding system name. After you exit the minibuffer, the specified coding system is used for the immediately following command.

So if the immediately following command is C-x C-f, for example, it reads the file using that coding system (and records the coding system for when you later save the file). Or if the immediately following command is C-x C-w, it writes the file using that coding system. When you specify the coding system for saving in this way, instead of with C-x RET f, there is no warning if the buffer contains characters that the coding system cannot handle.

Other file commands affected by a specified coding system include C-x i and C-x C-v, as well as the other-window variants of C-x C-f. C-x RET c also affects commands that start subprocesses, including M-x shell (see Shell). If the immediately following command does not use the coding system, then C-x RET c ultimately has no effect.

An easy way to visit a file with no conversion is with the M-x find-file-literally command. See Visiting.

The default value of the variable buffer-file-coding-system specifies the choice of coding system to use when you create a new file. It applies when you find a new file, and when you create a buffer and then save it in a file. Selecting a language environment typically sets this variable to a good choice of default coding system for that language environment.

If you visit a file with a wrong coding system, you can correct this with C-x RET r (revert-buffer-with-coding-system). This visits the current file again, using a coding system you specify.

If a piece of text has already been inserted into a buffer using the wrong coding system, you can redo the decoding of it using M-x recode-region. This prompts you for the proper coding system, then for the wrong coding system that was actually used, and does the conversion. It first encodes the region using the wrong coding system, then decodes it again using the proper coding system.