elisp: Decoding Output
36.9.3 Decoding Process Output
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When Emacs writes process output directly into a multibyte buffer, it
decodes the output according to the process output coding system. If
the coding system is ‘raw-text’ or ‘no-conversion’, Emacs converts the
unibyte output to multibyte using ‘string-to-multibyte’, and inserts the
resulting multibyte text.
You can use ‘set-process-coding-system’ to specify which coding
system to use (
Process Information). Otherwise, the coding
system comes from ‘coding-system-for-read’, if that is non-‘nil’; or
else from the defaulting mechanism (Default Coding Systems). If
the text output by a process contains null bytes, Emacs by default uses
‘no-conversion’ for it; see inhibit-null-byte-detection Lisp and
Coding Systems, for how to control this behavior.
*Warning:* Coding systems such as ‘undecided’, which determine the
coding system from the data, do not work entirely reliably with
asynchronous subprocess output. This is because Emacs has to process
asynchronous subprocess output in batches, as it arrives. Emacs must
try to detect the proper coding system from one batch at a time, and
this does not always work. Therefore, if at all possible, specify a
coding system that determines both the character code conversion and the
end of line conversion—that is, one like ‘latin-1-unix’, rather than
‘undecided’ or ‘latin-1’.
When Emacs calls a process filter function, it provides the process
output as a multibyte string or as a unibyte string according to the
process’s filter coding system. Emacs decodes the output according to
the process output coding system, which usually produces a multibyte
string, except for coding systems such as ‘binary’ and ‘raw-text’.
Info Catalog
elisp: Filter Functions
elisp: Output from Processes
elisp: Accepting Output