popen(3)						     Library Functions Manual							  popen(3)

NAME

       popen -	Initiates a pipe to a process

LIBRARY

       Standard C Library (libc.so, libc.a)

SYNOPSIS

       #include <stdio.h>

       FILE *popen (
	       const char *command,
	       const char *type );

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       popen():  XPG4, XPG4-UNIX

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS

       Points to a null-terminated string containing a shell command line.  Points to a null-terminated string containing an I/O mode.

DESCRIPTION

       The  popen() function creates a pipe between the calling program and a shell command to be executed.  It returns a pointer to a FILE struc-
       ture for the stream.

       If the type parameter is the value r, the calling program can read from the standard output of the command by  reading  from  the  returned
       file  stream.  If  the  type parameter is the value w, the calling program can write to the standard input of the command by writing to the
       returned file stream.

       Because open files are shared, a type r command can be used as an input filter and a type w command as an output filter.

NOTES

       Programs using the popen() function to invoke an output filter should beware of possible deadlock caused by output data	remaining  in  the
       program's  buffer.   This  can be avoided by either using the setbuf() function to ensure that the output stream is unbuffered, or by using
       the fflush() function to ensure that all buffered data is flushed before calling the pclose() function.	If the original processes and  the
       process	started  with  the  popen()  function  concurrently  read or write a common file, neither should use buffered I/O. If they do, the
       results are unpredictable.

RETURN VALUES

       Upon successful completion, the popen() function returns a pointer to the FILE structure for the opened stream.	In case of  error  because
       files or processes could not be created, the popen() function returns a null pointer.

RELATED INFORMATION

       Functions: exec(2), fork(2), fclose(3), fopen(3), pclose(3), pipe(2), setbuf(3)

       Standards: standards(5) delim off

																	  popen(3)