call-process-region is a built-in function in `C source code'.

(call-process-region START END PROGRAM &optional DELETE BUFFER DISPLAY &rest ARGS)

Send text from START to END to a synchronous process running PROGRAM.
The remaining arguments are optional.
Delete the text if fourth arg DELETE is non-nil.

Insert output in BUFFER before point; t means current buffer; nil for
BUFFER means discard it; 0 means discard and don't wait; and `(:file
FILE)', where FILE is a file name string, means that it should be
written to that file (if the file already exists it is overwritten).
BUFFER can also have the form (REAL-BUFFER STDERR-FILE); in that case,
REAL-BUFFER says what to do with standard output, as above,
while STDERR-FILE says what to do with standard error in the child.
STDERR-FILE may be nil (discard standard error output),
t (mix it with ordinary output), or a file name string.

Sixth arg DISPLAY non-nil means redisplay buffer as output is inserted.
Remaining args are passed to PROGRAM at startup as command args.

If BUFFER is 0, `call-process-region' returns immediately with value nil.
Otherwise it waits for PROGRAM to terminate
and returns a numeric exit status or a signal description string.
If you quit, the process is killed with SIGINT, or SIGKILL if you quit again.