Question

I need to run a Linux CLI command and get its stdout output from C.

I can use pipe() to create a pipe, then fork/exec, redirecting child’s stdout descriptor into the pipe before calling exec(), and reading from the pipe in parent. Plus I’ll need to wait on the child.

Is there a simple call to do fork + redirect + exec + wait, like system() does fork + exec + wait, only system() doesn’t do the redirect.

There’s popen(), which does fork + redirect + exec, but doesn’t do wait, so I can’t get exit status.

Answer 1

Is this it?

 NAME        popen, pclose - process I/O  SYNOPSIS        #include <stdio.h>           FILE *popen(const char *command, const char *type);         int pclose(FILE *stream);  DESCRIPTION        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 type 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().