The
popen()
function opens a process by creating a pipe, forking, and invoking the
shell. Since a pipe is by definition unidirectional, the
type
argument may specify only reading or writing, not both; the resulting
stream is correspondingly read-only or write-only.
The
command
argument is a pointer to a null-terminated string containing a shell
command line. This command is passed to
/bin/sh
using the
-c
flag; interpretation, if any, is performed by the shell. The
mode
argument is a pointer to a null-terminated string which must be either `r'
for reading or `w' for writing.
The return value from
popen()
is a normal standard I/O stream in all respects save that it must be closed
with
pclose()
rather than
fclose() .
Writing to such a stream writes to the standard input of the command; the
command's standard output is the same as that of the process that called
popen() ,
unless this is altered by the command itself. Conversely, reading from a
``popened'' stream reads the command's standard output, and the command's
standard input is the same as that of the process that called
popen .
Note that output
popen
streams are fully buffered by default.
The
pclose
function waits for the associated process to terminate and returns the exit
status of the command as returned by
wait4 .