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 #define streq(a, b) (!strcmp((a), (b)))
  27
  28 static void stdin_to_stream(char *buf, ssize_t r, FILE *outf) {
  29         while (r > 0) {
  30                 if (fwrite(buf, r*sizeof(char), 1, outf) < 1) {
  31                         fprintf(stderr, "Write error\n");
  32                         exit(EXIT_FAILURE);
  33                 }
  34                 r = read(0, buf, BUFSIZ*sizeof(char));
  35         }
  36         if (r == -1) {
  37                 perror("read");
  38                 exit(EXIT_FAILURE);
  39         }
  40 }
  41
  42 int main(int argc, char **argv) {
  43         ssize_t r;
  44         int run_if_empty;
  45         char **argv_exec;
  46         int fds[2];
  47         int child_status;
  48         pid_t child_pid;
  49         char buf[BUFSIZ];
  50         FILE *outf;
  51
  52         if ((argc < 2) || ((argc == 2) && streq(argv[1], "-n"))) {
  53                 fprintf(stderr, "Usage: ifne [-n] command [args]\n");
  54                 return EXIT_FAILURE;
  55         }
  56
  57         if (streq(argv[1], "-n")) {
  58                 run_if_empty = 1;
  59                 argv_exec = &argv[2];
  60         } else {
  61                 run_if_empty = 0;
  62                 argv_exec = &argv[1];
  63         }
  64
  65         r = read(0, buf, BUFSIZ*sizeof(char));
  66
  67         if ((r == 0) && !run_if_empty)
  68                 return EXIT_SUCCESS;
  69         else if (r == -1) {
  70                 perror("read");
  71                 return EXIT_FAILURE;
  72         }
  73
  74         if (pipe(fds)) {
  75                 perror("pipe");
  76                 return EXIT_FAILURE;
  77         }
  78
  79         if (r && run_if_empty) {
  80                 /* don't run the subcommand if we read something from stdin and -n was set */
  81                 /* But write stdin to stdout so ifne -n can be piped without sucking the stream */
  82                 stdin_to_stream(buf, r, stdout);
  83                 return EXIT_SUCCESS;
  84         }
  85
  86         child_pid = fork();
  87         if (!child_pid) {
  88                 /* child process: rebind stdin and exec the subcommand */
  89                 close(fds[1]);
  90                 if (dup2(fds[0], 0)) {
  91                         perror("dup2");
  92                         return EXIT_FAILURE;
  93                 }
  94
  95                 execvp(*argv_exec, argv_exec);
  96                 perror(*argv_exec);
  97                 close(fds[0]);
  98                 return EXIT_FAILURE;
  99         } else if (child_pid == -1) {
 100                 perror("fork");
 101                 return EXIT_FAILURE;
 102         }
 103
 104         /* Parent: write stdin to fds[1] */
 105         close(fds[0]);
 106         outf = fdopen(fds[1], "w");
 107         if (! outf) {
 108                 perror("fdopen");
 109                 exit(1);
 110         }
 111
 112         stdin_to_stream(buf, r, outf);
 113         fclose(outf);
 114
 115         if (waitpid(child_pid, &child_status, 0) != child_pid) {
 116                 perror("waitpid");
 117                 return EXIT_FAILURE;
 118         }
 119         if (WIFEXITED(child_status)) {
 120                 return (WEXITSTATUS(child_status));
 121         } else if (WIFSIGNALED(child_status)) {
 122                 raise(WTERMSIG(child_status));
 123                 return EXIT_FAILURE;
 124         }
 125
 126         return EXIT_FAILURE;
 127 }