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I.1.3.7 process-connection-type—a variable

Variable: process-connection-type ¶

This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-‘nil’, then ptys are used, when available. Otherwise, pipes are used. The value of ‘process-connection-type’ takes effect when ‘make-process’ or ‘start-process’ is called. So you can specify how to communicate with one subprocess by binding the variable around the call to these functions.

Note that the value of this variable is ignored when ‘make-process’ is called with a non-‘nil’ value of the ‘:stderr’ parameter; in that case, Emacs will communicate with the process using pipes. It is also ignored if ptys are unavailable (MS-Windows).

To determine whether a given subprocess actually got a pipe or a pty, use the function process-tty-name.