popen(3)
Name
popen, pclose − initiate I/O to/from a process
Syntax
#include <stdio.h>
FILE *popen(command, type)
char *command, *type;
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. It 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.
Environment
Differs from the System V definition in that ENFILE is not a possible error condition.
Diagnostics
The popen routine returns a null pointer if files or processes cannot be created, or the shell cannot be accessed.
The pclose routine returns −1 if stream is not associated with a ‘popened’ command.
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 instance, with fflush. For further information, see fclose(.).
The popen routine always calls sh, and never calls csh.