p2open(3G)

NAME
     p2open, p2close - open, close pipes to and from a command

SYNOPSIS
     cc [flag ...] file ...  -lgen [library ...]

     #include <libgen.h>

     int p2open (const char *cmd, FILE *fp[2]);

     int p2close (FILE *fp[2]);

DESCRIPTION
     p2open forks and execs a shell running the command line pointed to by
     cmd.  On return, fp[0] points to a FILE pointer to write the command's
     standard input and fp[1] points to a FILE pointer to read from the
     command's standard output.  In this way the program has control over the
     input and output of the command.

     The function returns 0 if successful; otherwise it returns -1.

     p2close is used to close the file pointers that p2open opened.  It waits
     for the process to terminate and returns the process status.  It returns
     0 if successful; otherwise it returns -1.

EXAMPLES
     #include <stdio.h>
     #include <libgen.h>
     main(argc,argv)
     int argc;
     char **argv;
     {
          FILE *fp[2];
          pid_t pid;
          char buf[16];
          pid=p2open("/usr/bin/cat", fp);
          if ( pid != 0 ) {
               fprintf(stderr, "p2open failed\n");
               exit(1);
          }
          write(fileno(fp[0]),"This is a test\n", 16);
          if(read(fileno(fp[1]), buf, 16) <=0)
               fprintf(stderr, "p2open failed\n");
          else
               write(1, buf, 16);
          (void)p2close(fp);
     }
SEE ALSO
     fclose(3S), popen(3S), setbuf(3S)

DIAGNOSTICS
     A common problem is having too few file descriptors.  p2close returns -1
     if the two file pointers are not from the same p2open.

NOTES
     Buffered writes on fp[0] can make it appear that the command is not
     listening.  Judiciously placed fflush calls or unbuffering fp[0] can be a
     big help; see fclose(3S).

     Many commands use buffered output when connected to a pipe.  That, too,
     can make it appear as if things are not working.

     Usage is not the same as for popen, although it is closely related.