Info Catalog elisp: Default Coding Systems elisp: Coding Systems elisp: Explicit Encoding

elisp: Specifying Coding Systems

 
 32.10.6 Specifying a Coding System for One Operation
 ----------------------------------------------------
 
 You can specify the coding system for a specific operation by binding
 the variables ‘coding-system-for-read’ and/or ‘coding-system-for-write’.
 
  -- Variable: coding-system-for-read
      If this variable is non-‘nil’, it specifies the coding system to
      use for reading a file, or for input from a synchronous subprocess.
 
      It also applies to any asynchronous subprocess or network stream,
      but in a different way: the value of ‘coding-system-for-read’ when
      you start the subprocess or open the network stream specifies the
      input decoding method for that subprocess or network stream.  It
      remains in use for that subprocess or network stream unless and
      until overridden.
 
      The right way to use this variable is to bind it with ‘let’ for a
      specific I/O operation.  Its global value is normally ‘nil’, and
      you should not globally set it to any other value.  Here is an
      example of the right way to use the variable:
 
           ;; Read the file with no character code conversion.
           (let ((coding-system-for-read 'no-conversion))
             (insert-file-contents filename))
 
      When its value is non-‘nil’, this variable takes precedence over
      all other methods of specifying a coding system to use for input,
      including ‘file-coding-system-alist’, ‘process-coding-system-alist’
      and ‘network-coding-system-alist’.
 
  -- Variable: coding-system-for-write
      This works much like ‘coding-system-for-read’, except that it
      applies to output rather than input.  It affects writing to files,
      as well as sending output to subprocesses and net connections.  It
      also applies to encoding command-line arguments with which Emacs
      invokes subprocesses.
 
      When a single operation does both input and output, as do
      ‘call-process-region’ and ‘start-process’, both
      ‘coding-system-for-read’ and ‘coding-system-for-write’ affect it.
 
  -- Variable: coding-system-require-warning
      Binding ‘coding-system-for-write’ to a non-‘nil’ value prevents
      output primitives from calling the function specified by
      ‘select-safe-coding-system-function’ (User-Chosen Coding
      Systems).  This is because ‘C-x RET c’
      (‘universal-coding-system-argument’) works by binding
      ‘coding-system-for-write’, and Emacs should obey user selection.
      If a Lisp program binds ‘coding-system-for-write’ to a value that
      might not be safe for encoding the text to be written, it can also
      bind ‘coding-system-require-warning’ to a non-‘nil’ value, which
      will force the output primitives to check the encoding by calling
      the value of ‘select-safe-coding-system-function’ even though
      ‘coding-system-for-write’ is non-‘nil’.  Alternatively, call
      ‘select-safe-coding-system’ explicitly before using the specified
      encoding.
 
  -- User Option: inhibit-eol-conversion
      When this variable is non-‘nil’, no end-of-line conversion is done,
      no matter which coding system is specified.  This applies to all
      the Emacs I/O and subprocess primitives, and to the explicit
      encoding and decoding functions (Explicit Encoding).
 
    Sometimes, you need to prefer several coding systems for some
 operation, rather than fix a single one.  Emacs lets you specify a
 priority order for using coding systems.  This ordering affects the
 sorting of lists of coding systems returned by functions such as
 ‘find-coding-systems-region’ (Lisp and Coding Systems).
 
  -- Function: coding-system-priority-list &optional highestp
      This function returns the list of coding systems in the order of
      their current priorities.  Optional argument HIGHESTP, if
      non-‘nil’, means return only the highest priority coding system.
 
  -- Function: set-coding-system-priority &rest coding-systems
      This function puts CODING-SYSTEMS at the beginning of the priority
      list for coding systems, thus making their priority higher than all
      the rest.
 
  -- Macro: with-coding-priority coding-systems &rest body...
      This macro execute BODY, like ‘progn’ does (progn
      Sequencing.), with CODING-SYSTEMS at the front of the priority list
      for coding systems.  CODING-SYSTEMS should be a list of coding
      systems to prefer during execution of BODY.
 

Info Catalog elisp: Default Coding Systems elisp: Coding Systems elisp: Explicit Encoding