ifne.c

   1 /*
   2  *
   3  * Copyright 2008 Javier Merino <cibervicho@gmail.com>
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License as published by the
   6  * Free Software Foundation; either version 2 of the License, or (at your
   7  * option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
  12  * Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along
  15  * with this program; if not, write to the Free Software Foundation, Inc.,
  16  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  17  *
  18  */
  19
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22 #include <unistd.h>
  23 #include <sys/wait.h>
  24 #include <sys/types.h>
  25 #include <string.h>
  26 #include <signal.h>
  27
  28 #define streq(a, b) (!strcmp((a), (b)))
  29
  30 static void stdin_to_stream(char *buf, ssize_t r, FILE *outf) {
  31         while (r > 0) {
  32                 if (fwrite(buf, r*sizeof(char), 1, outf) < 1) {
  33                         fprintf(stderr, "Write error\n");
  34                         exit(EXIT_FAILURE);
  35                 }
  36                 r = read(0, buf, BUFSIZ*sizeof(char));
  37         }
  38         if (r == -1) {
  39                 perror("read");
  40                 exit(EXIT_FAILURE);
  41         }
  42 }
  43
  44 int main(int argc, char **argv) {
  45         ssize_t r;
  46         int run_if_empty;
  47         char **argv_exec;
  48         int fds[2];
  49         int child_status;
  50         pid_t child_pid;
  51         char buf[BUFSIZ];
  52         FILE *outf;
  53
  54         if ((argc < 2) || ((argc == 2) && streq(argv[1], "-n"))) {
  55                 fprintf(stderr, "Usage: ifne [-n] command [args]\n");
  56                 return EXIT_FAILURE;
  57         }
  58
  59         if (streq(argv[1], "-n")) {
  60                 run_if_empty = 1;
  61                 argv_exec = &argv[2];
  62         } else {
  63                 run_if_empty = 0;
  64                 argv_exec = &argv[1];
  65         }
  66
  67         r = read(0, buf, BUFSIZ*sizeof(char));
  68
  69         if ((r == 0) && !run_if_empty)
  70                 return EXIT_SUCCESS;
  71         else if (r == -1) {
  72                 perror("read");
  73                 return EXIT_FAILURE;
  74         }
  75
  76         if (pipe(fds)) {
  77                 perror("pipe");
  78                 return EXIT_FAILURE;
  79         }
  80
  81         if (r && run_if_empty) {
  82                 /* don't run the subcommand if we read something from stdin and -n was set */
  83                 /* But write stdin to stdout so ifne -n can be piped without sucking the stream */
  84                 stdin_to_stream(buf, r, stdout);
  85                 return EXIT_SUCCESS;
  86         }
  87
  88         child_pid = fork();
  89         if (!child_pid) {
  90                 /* child process: rebind stdin and exec the subcommand */
  91                 close(fds[1]);
  92                 if (dup2(fds[0], 0)) {
  93                         perror("dup2");
  94                         return EXIT_FAILURE;
  95                 }
  96
  97                 execvp(*argv_exec, argv_exec);
  98                 perror(*argv_exec);
  99                 close(fds[0]);
 100                 return EXIT_FAILURE;
 101         } else if (child_pid == -1) {
 102                 perror("fork");
 103                 return EXIT_FAILURE;
 104         }
 105
 106         /* Parent: write stdin to fds[1] */
 107         close(fds[0]);
 108         outf = fdopen(fds[1], "w");
 109         if (! outf) {
 110                 perror("fdopen");
 111                 exit(1);
 112         }
 113
 114         stdin_to_stream(buf, r, outf);
 115         fclose(outf);
 116
 117         if (waitpid(child_pid, &child_status, 0) != child_pid) {
 118                 perror("waitpid");
 119                 return EXIT_FAILURE;
 120         }
 121         if (WIFEXITED(child_status)) {
 122                 return (WEXITSTATUS(child_status));
 123         } else if (WIFSIGNALED(child_status)) {
 124                 raise(WTERMSIG(child_status));
 125                 return EXIT_FAILURE;
 126         }
 127
 128         return EXIT_FAILURE;
 129 }