popen(3s)
NAME
popen, pclose − initiate I/O to/from a process
SYNTAX
#include <stdio.h>
FILE *popen(command, type)
char *command, *type;
int pclose(stream)
FILE *stream;
DESCRIPTION
The arguments to popen are pointers to null-terminated strings containing, respectively, a shell command line and an I/O mode, either r for reading or w for writing. The popen subroutine creates a pipe between the calling process and the command to be executed. The value returned is a stream pointer that can be used (as appropriate) to write to the standard input of the command or read from its standard output.
A stream opened by popen should be closed by pclose, which waits for the associated process to terminate and returns the exit status of the command.
Because open files are shared, a type r command may be used as an input filter, and a type w as an output filter.
RESTRICTIONS
Buffered reading before opening an input filter may leave the standard input of that filter mispositioned. Similar problems with an output filter may be forestalled by careful buffer flushing, for example with fflush. For further information, see fclose(3s).
DIAGNOSTICS
The popen subroutine returns a null pointer if files or processes cannot be created, or the Shell cannot be accessed.
The pclose subroutine returns −1 if stream is not associated with a popen call.