POPEN - phpMan

POPEN(3)                   Linux Programmer’s Manual                  POPEN(3)



NAME
       popen, pclose - process I/O

SYNOPSIS
       #include <stdio.h>

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

       int pclose(FILE *stream);

DESCRIPTION
       The  popen() function opens a process by creating a pipe, forking, and invoking the
       shell.  Since a pipe is by definition unidirectional, the type argument may specify
       only  reading  or  writing, not both; the resulting stream is correspondingly read-
       only or write-only.

       The command argument is a pointer to a null-terminated string  containing  a  shell
       command line.  This command is passed to /bin/sh using the -c flag; interpretation,
       if any, is performed by the shell.  The type argument is a pointer to a null-termi-
       nated string which must be either ‘r’ for reading or ‘w’ for writing.

       The  return value from popen() is a normal standard I/O stream in all respects save
       that it must be closed with pclose() rather  than  fclose().   Writing  to  such  a
       stream  writes  to the standard input of the command; the command’s standard output
       is the same as that of the process that called popen(), unless this is  altered  by
       the  command  itself.  Conversely, reading from a ‘‘popened’’ stream reads the com-
       mand’s standard output, and the command’s standard input is the same as that of the
       process that called popen.

       Note that output popen streams are fully buffered by default.

       The  pclose  function waits for the associated process to terminate and returns the
       exit status of the command as returned by wait4.

RETURN VALUE
       The popen function returns NULL if the fork(2) or pipe(2) calls fail, or if it can-
       not allocate memory.

       The  pclose  function  returns -1 if wait4 returns an error, or some other error is
       detected.

ERRORS
       The popen function does not set errno if memory allocation fails.  If the  underly-
       ing  fork()  or  pipe() fails, errno is set appropriately.  If the type argument is
       invalid, and this condition is detected, errno is set to EINVAL.

       If pclose() cannot obtain the child status, errno is set to ECHILD.

CONFORMING TO
       POSIX.2

BUGS
       Since the standard input of a command opened for reading  shares  its  seek  offset
       with  the  process that called popen(), if the original process has done a buffered
       read, the command’s input position may not be as expected.  Similarly,  the  output
       from a command opened for writing may become intermingled with that of the original
       process.  The latter can be avoided by calling fflush(3) before popen.

       Failure to execute the shell is indistinguishable from the shell’s failure to  exe-
       cute command, or an immediate exit of the command.  The only hint is an exit status
       of 127.

HISTORY
       A popen() and a pclose() function appeared in Version 7 AT&T UNIX.

SEE ALSO
       fork(2), sh(1), pipe(2), wait4(2), fflush(3), fclose(3), fopen(3),  stdio(3),  sys-
       tem(3)



BSD MANPAGE                       1998-05-07                          POPEN(3)

Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2008-12-02 01:14 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)