popen(3S)                    DG/UX 5.4 Rel. 2.01                   popen(3S)


NAME
       popen, pclose - initiate pipe to/from a process

SYNOPSIS
       #include <stdio.h>

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

       int pclose (FILE *stream);

DESCRIPTION
       popen creates a pipe between the calling program and the command to
       be executed.  The arguments to popen are pointers to null-terminated
       strings.  command consists of a shell command line.  /bin/sh is used
       to execute this command line.  type is an I/O mode, either r for
       reading or w for writing.  The value returned is a stream pointer
       such that one can write to the standard input of the command, if the
       I/O mode is w, by writing to the file stream [see intro(3)]; and one
       can read from the standard output of the command, if the I/O mode is
       r, by reading from the file stream.

       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.

EXAMPLE
       Here is an example of a typical call:

              #include <stdio.h>
              #include <stdlib.h>

              main()
              {
                   char *cmd = "/usr/bin/ls *.c";
                   char buf[BUFSIZ];
                   FILE *ptr;

                   if ((ptr = popen(cmd, "r")) != NULL)
                        while (fgets(buf, BUFSIZ, ptr) != NULL)
                             (void) printf("%s", buf);
                   return 0;
              }

       This program will print on the standard output [see stdio(3S)] all
       the file names in the current directory that have a .c suffix.

SEE ALSO
       pipe(2), signal(2), wait(2), waitpid(2), fclose(3S), fopen(3S),
       stdio(3S), system(3S).





Licensed material--property of copyright holder(s)                         1

popen(3S)                    DG/UX 5.4 Rel. 2.01                   popen(3S)


DIAGNOSTICS
       popen returns a null pointer if files or processes cannot be created.

       pclose returns -1 if stream is not associated with a popened command
       or waitpid (used in the implementation of pclose) returns a -1 for
       some reason (see NOTES below).

NOTES
       If the original and popened processes concurrently read or write a
       common file, neither should use buffered I/O.  Problems with an
       output filter may be forestalled by careful buffer flushing, e.g.,
       with fflush [see fclose(3S)].

       If SIGCHLD is set to SIGIGN, pclose will return a -1 with errno set
       to ECHILD (the results of calling waitpid).

       A security hole exists through the IFS and PATH environment variables
       if setuid is enabled.  Full pathnames should be used (or PATH reset)
       and IFS should be set to space and tab (" \t").






































Licensed material--property of copyright holder(s)                         2