lib/readpipe.c

   1 /* Open a pipe to read from a program without intermediary sh.
   2    Copyright (C) 1992, 1997 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 /* Written by David MacKenzie.  */
  19
  20 #if HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #include <stdio.h>
  25
  26 #if __STDC__
  27 #include <stdarg.h>
  28 #else
  29 #include <varargs.h>
  30 #endif
  31
  32 #if HAVE_UNISTD_H
  33 # include <unistd.h>
  34 #endif
  35
  36 /* Open a pipe to read from a program without intermediary sh.  Checks
  37    PATH.  Sample use:
  38
  39    stream = readpipe ("progname", "arg1", "arg2", (char *) 0);
  40
  41    Return 0 on error.  */
  42
  43 #if __STDC__
  44 FILE *
  45 readpipe (char *progname, ...)
  46 #else
  47 FILE *
  48 readpipe (va_alist)
  49 #endif
  50 {
  51 #if ! __STDC__
  52   char *progname;
  53 #endif
  54   int fds[2];
  55   va_list ap;
  56   char *args[100];
  57   int argno = 0;
  58
  59   /* Copy arguments into `args'. */
  60 #if __STDC__
  61   va_start (ap, progname);
  62 #else
  63   va_start (ap);
  64   progname = va_arg (ap, char *);
  65 #endif
  66   args[argno++] = progname;
  67   while ((args[argno++] = va_arg (ap, char *)) != NULL)
  68     ;
  69   va_end (ap);
  70
  71   if (pipe (fds) == -1)
  72     return 0;
  73
  74   switch (fork ())
  75     {
  76     case 0:                     /* Child.  Write to pipe. */
  77       close (fds[0]);           /* Not needed. */
  78       if (fds[1] != 1)          /* Redirect 1 (stdout) only if needed.  */
  79         {
  80           close (1);            /* We don't want the old stdout. */
  81           if (dup (fds[1]) == 0)/* Maybe stdin was closed. */
  82             {
  83               dup (fds[1]);     /* Guaranteed to dup to 1 (stdout). */
  84               close (0);
  85             }
  86           close (fds[1]);       /* No longer needed. */
  87         }
  88       execvp (args[0], args);
  89       _exit (2);                /* 2 for `cmp'. */
  90     case -1:                    /* Error. */
  91       return 0;
  92     default:                    /* Parent.  Read from pipe. */
  93       close (fds[1]);           /* Not needed. */
  94       return fdopen (fds[0], "r");
  95     }
  96 }