POPEN(3S-SVR4)      RISC/os Reference Manual       POPEN(3S-SVR4)



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.

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.





                        Printed 11/19/92                   Page 1

POPEN(3S-SVR4)      RISC/os Reference Manual       POPEN(3S-SVR4)



SEE ALSO
     pipe(2), wait(2), 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.

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

     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.



































 Page 2                 Printed 11/19/92