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 _p_o_p_e_n 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 pro‐
       cess 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 _p_o_p_e_n should be closed by _p_c_l_o_s_e,  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
       _P_o_p_e_n  returns  a null pointer if files or processes cannot be created,
       or the shell cannot be accessed.

       _P_c_l_o_s_e returns -1 if _s_t_r_e_a_m 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 _f_f_l_u_s_h_, see _f_c_l_o_s_e(3S).

       _P_o_p_e_n always calls _s_h, never calls _c_s_h.



7th Edition                      May 15, 1985                         POPEN(3)