# 2.11BSD#431 - /usr/man/cat3/popen.0

    POPEN(3)	    UNIX Programmer's Manual		 POPEN(3)

    NAME
         popen, pclose - initiate I/O to/from a process

    SYNOPSIS
         #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.

    SEE ALSO
         pipe(2), fopen(3S), fclose(3S), system(3), wait(2), sh(1)

    DIAGNOSTICS
         Popen returns a null pointer if files or processes cannot be
         created, or the shell cannot be accessed.

         Pclose returns -1 if stream is not associated with a
         `popened' command.

    BUGS
         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, see fclose(3S).

         Popen always calls sh, never calls csh.

    Printed 11/26/99	  May 15, 1985				1

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