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BSD 2.11 - man page for popen (bsd section 3)

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POPEN(3)										 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  fil-
       ter  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.

7th Edition				   May 15, 1985 				 POPEN(3)
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