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POPEN(3)                   Library Functions Manual                   POPEN(3)



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

SYNOPSIS
       #include <&lt;stdio.h>&gt;

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

       pclose(stream)
       FILE *stream;

DESCRIPTION
       The arguments to popen are pointers to null-terminated strings contain-
       ing 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(3).

       Popen always calls sh, never calls csh.



                                 18 July 1983                         POPEN(3)