mispipe.c

   1 /*
   2  * mispipe: written by Nathanael Nerode.
   3  *
   4  * Copyright 2004 Nathanael Nerode.
   5  *
   6  * Licensed under the GPL version 2 or above, and dual-licensed under the
   7  * following license:
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a
  10  * copy of this software and associated documentation files (the "Software"),
  11  * to deal in the Software without restriction, including without limitation
  12  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  13  * and/or sell copies of the Software, and to permit persons to whom the
  14  * Software is furnished to do so, subject to the following conditions:
  15  *
  16  * The above copyright notice and this permission notice shall be included in
  17  * all copies or substantial portions of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  22  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  25  * THE SOFTWARE.
  26  */
  27
  28 /*
  29  * Usage: mispipe <command1> <command2>
  30  * Run <command1> | <command2>, but return with the exit status of <command1>.
  31  *
  32  * This is designed for a very specific purpose: logging.
  33  * "foo | logger -t foo"
  34  * will return with the exit status of logger, not that of foo.
  35  * "mispipe foo 'logger -t foo'"
  36  * will return with the exit status of foo.
  37  */
  38
  39 /*
  40  * To do:
  41  * Make this into a fancy, internationalized, option-handling hellbeast.
  42  * (But why bother?  It does its job quite well.)
  43  */
  44
  45 #include <errno.h> /* errno */
  46 #include <sys/types.h>
  47 #include <unistd.h> /* pipe(), fork(),... */
  48 #include <stdlib.h> /* system() */
  49 #include <sys/wait.h> /* waitpid(), etc. */
  50 #include <stdio.h>
  51 #include <stdarg.h> /* va_list, for error() */
  52
  53 static const char* progname; /* Stores argv[0] */
  54 static int filedes[2]; /* Stores pipe file descriptors */
  55
  56 /* Subroutine for 'warning' and 'error' which prefixes progname */
  57 static void warning_prefix(void) {
  58         fputs(progname, stderr);
  59         fputs(": ", stderr);
  60 }
  61
  62 /* Issue a warning, then die */
  63 __attribute__(( noreturn, format (printf, 1, 2) ))
  64 static void error(const char* formatstr, ...) {
  65         va_list ap;
  66         va_start(ap, formatstr);
  67         warning_prefix();
  68         vfprintf(stderr, formatstr, ap);
  69         va_end(ap);
  70         exit(1);
  71 }
  72
  73 /* Issue a warning, then die, with errno */
  74 __attribute__(( noreturn ))
  75 static void error_with_errno(const char* message) {
  76         int saved_errno;
  77         saved_errno=errno;
  78         warning_prefix();
  79         fputs(message, stderr);
  80         fputs(": error number ", stderr);
  81         fprintf(stderr, "%i\n", saved_errno);
  82         exit(1);
  83 }
  84
  85 /* Convert 'wait'/'system'-style exit status to 'exit'-style exit status */
  86 __attribute__(( const ))
  87 static int shorten_status(int status_big) {
  88         if (WIFEXITED(status_big))
  89                 return WEXITSTATUS(status_big);
  90         if (WIFSIGNALED(status_big))
  91                 return 128+WTERMSIG(status_big);
  92         if (WIFSTOPPED(status_big))
  93                 return 128+WSTOPSIG(status_big);
  94 #ifdef WCOREDUMP
  95         if (WCOREDUMP(status_big))
  96                  error("Ow, somebody dumped core!");
  97 #endif
  98         error("shorten_status got an invalid status (?!)");
  99 }
 100
 101 /* All the work for command 2. */
 102 __attribute__(( noreturn ))
 103 static void subprocess2(const char* cmd) {
 104         /* Close the old standard input. */
 105         if (close(0))
 106                 error_with_errno("Failed (in child) closing standard input");
 107         /* Make the reading end of the pipe the new standard input. */
 108         if (dup2(filedes[0], 0) == -1)
 109                 error_with_errno("Failed (in child) redefining standard input");
 110         /* Close the original file descriptor for it */
 111         if (close(filedes[0]))
 112                 error_with_errno("Failed (in child) closing filedes[0]");
 113         /* Close the other end of the pipe. */
 114         if (close(filedes[1]))
 115                 error_with_errno("Failed (in child) closing filedes[1]");
 116         /* Do the second command, and throw away the exit status. */
 117         if (system(cmd)) {}
 118         /* Close the standard input. */
 119         if (close(0))
 120                 error_with_errno("Failed (in child) closing standard output "
 121                         " (while cleaning up)");
 122         exit(0);
 123 }
 124
 125 int main (int argc, const char ** argv) {
 126         int status_big; /* Exit status, 'wait' and 'system' style */
 127         pid_t child2_pid;
 128         pid_t dead_pid;
 129
 130         /* Set progname */
 131         progname = argv[0];
 132
 133         /* Verify arguments */
 134         if (argc != 3)
 135                 error("Wrong number of args, aborting\n");
 136         /* Open a new pipe */
 137         if (pipe(filedes))
 138                 error_with_errno("pipe() failed");
 139
 140         /* Fork to run second command */
 141         child2_pid = fork();
 142         if (child2_pid == 0)
 143                 subprocess2(argv[2]);
 144         if (child2_pid == -1)
 145                 error_with_errno("fork() failed");
 146
 147         /* Run first command inline (seriously!) */
 148         /* Close standard output. */
 149         if (close(1))
 150                 error_with_errno("Failed closing standard output");
 151         /* Make the writing end of the pipe the new standard output. */
 152         if (dup2(filedes[1], 1) == -1)
 153                 error_with_errno("Failed redefining standard output");
 154         /* Close the original file descriptor for it. */
 155         if (close(filedes[1]))
 156                 error_with_errno("Failed closing filedes[1]");
 157         /* Close the other end of the pipe. */
 158         if (close(filedes[0]))
 159                 error_with_errno("Failed closing filedes[0]");
 160         /* Do the first command, and (crucially) get the status. */
 161         status_big = system(argv[1]);
 162
 163         /* Close standard output. */
 164         if (close(1))
 165                 error_with_errno("Failed closing standard output (while cleaning up)");
 166
 167         /* Wait for the other process to exit. */
 168         /* We don't care about the status. */
 169         dead_pid = waitpid(child2_pid, NULL, WUNTRACED);
 170         if (dead_pid == -1) {
 171                 error_with_errno("waitpid() failed");
 172         }
 173         else if (dead_pid != child2_pid) {
 174                 error("waitpid(): Who died? %i\n", dead_pid);
 175         }
 176
 177         /* Return the desired exit status. */
 178         return shorten_status(status_big);
 179 }