popen(), pclose() - process I/O with pipes
#include <stdio.h>
FILE * popen (const char *command, const char *type)
int pclose (FILE *stream)
The popen(3) 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(3) is a normal standard I/O stream in all respects save that it must be closed with pclose(3) rather than fclose(3). 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(3) 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(3).
Note that output popen(3) streams are fully buffered by default.
The pclose(3) function waits for the associated process to terminate and returns the exit status of the command.
The popen(3) function returns NULL if the fork(2) or pipe(2) calls fail, or if it cannot allocate memory.
On success, the pclose(3) function the exit status of the terminating command. On failure, pclose(3) returns -1 if stream is not associated with a popen(3)'ed command, or if stream already pclose(3)'d
The popen(3) function does not reliably set errno
sh(1)
fork(2)
pipe(2)
fflush(3)
fclose(3)
fopen(3)
system(3)