popen(3S)                      DG/UX 5.4R3.00                      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.  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.


   Considerations for Threads Programming
                     +---------+-----------------------------+
                     |         |                      async- |
                     |function | reentrant   cancel   cancel |
                     |         |              point    safe  |
                     +---------+-----------------------------+
                     |pclose   |     N          -        -   |
                     |popen    |     N          -        -   |
                     +---------+-----------------------------+

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;



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

popen(3S)                      DG/UX 5.4R3.00                      popen(3S)


              }

       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), reentrant(3), fclose(3S),
       fopen(3S), stdio(3S), system(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.  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