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 #ifdef __sun
  27 #include <signal.h> /* raise() */
  28 #endif
  29
  30 #define streq(a, b) (!strcmp((a), (b)))
  31
  32 static void stdin_to_stream(char *buf, ssize_t r, FILE *outf) {
  33         while (r > 0) {
  34                 if (fwrite(buf, r*sizeof(char), 1, outf) < 1) {
  35                         fprintf(stderr, "Write error\n");
  36                         exit(EXIT_FAILURE);
  37                 }
  38                 r = read(0, buf, BUFSIZ*sizeof(char));
  39         }
  40         if (r == -1) {
  41                 perror("read");
  42                 exit(EXIT_FAILURE);
  43         }
  44 }
  45
  46 int main(int argc, char **argv) {
  47         ssize_t r;
  48         int run_if_empty;
  49         char **argv_exec;
  50         int fds[2];
  51         int child_status;
  52         pid_t child_pid;
  53         char buf[BUFSIZ];
  54         FILE *outf;
  55
  56         if ((argc < 2) || ((argc == 2) && streq(argv[1], "-n"))) {
  57                 fprintf(stderr, "Usage: ifne [-n] command [args]\n");
  58                 return EXIT_FAILURE;
  59         }
  60
  61         if (streq(argv[1], "-n")) {
  62                 run_if_empty = 1;
  63                 argv_exec = &argv[2];
  64         } else {
  65                 run_if_empty = 0;
  66                 argv_exec = &argv[1];
  67         }
  68
  69         r = read(0, buf, BUFSIZ*sizeof(char));
  70
  71         if ((r == 0) && !run_if_empty)
  72                 return EXIT_SUCCESS;
  73         else if (r == -1) {
  74                 perror("read");
  75                 return EXIT_FAILURE;
  76         }
  77
  78         if (pipe(fds)) {
  79                 perror("pipe");
  80                 return EXIT_FAILURE;
  81         }
  82
  83         if (r && run_if_empty) {
  84                 /* don't run the subcommand if we read something from stdin and -n was set */
  85                 /* But write stdin to stdout so ifne -n can be piped without sucking the stream */
  86                 stdin_to_stream(buf, r, stdout);
  87                 return EXIT_SUCCESS;
  88         }
  89
  90         child_pid = fork();
  91         if (!child_pid) {
  92                 /* child process: rebind stdin and exec the subcommand */
  93                 close(fds[1]);
  94                 if (dup2(fds[0], 0)) {
  95                         perror("dup2");
  96                         return EXIT_FAILURE;
  97                 }
  98
  99                 execvp(*argv_exec, argv_exec);
 100                 perror(*argv_exec);
 101                 close(fds[0]);
 102                 return EXIT_FAILURE;
 103         } else if (child_pid == -1) {
 104                 perror("fork");
 105                 return EXIT_FAILURE;
 106         }
 107
 108         /* Parent: write stdin to fds[1] */
 109         close(fds[0]);
 110         outf = fdopen(fds[1], "w");
 111         if (! outf) {
 112                 perror("fdopen");
 113                 exit(1);
 114         }
 115
 116         stdin_to_stream(buf, r, outf);
 117         fclose(outf);
 118
 119         if (waitpid(child_pid, &child_status, 0) != child_pid) {
 120                 perror("waitpid");
 121                 return EXIT_FAILURE;
 122         }
 123         if (WIFEXITED(child_status)) {
 124                 return (WEXITSTATUS(child_status));
 125         } else if (WIFSIGNALED(child_status)) {
 126                 raise(WTERMSIG(child_status));
 127                 return EXIT_FAILURE;
 128         }
 129
 130         return EXIT_FAILURE;
 131 }