arg.c - arg

(50 lines)
   1 /* 
   2  * arg - A simple C program by Bruce Hill for parsing command line arguments
   3  *   Licensed under the MIT license (see LICENSE for details).
   4  *
   5  *   Example: arg --foo a b --foo=blah --baz -xyz
   6  *     - Prints "blah" and exits with success
   7  *   Example: arg --nope a b --foo=blah --baz -xyz
   8  *     - Prints nothing and exits with failure
   9  *   Example: arg -y a b --foo=blah --baz -xyz
  10  *     - Prints nothing and exits with success
  11  */
  12 #include <stdio.h>
  13 #include <string.h>
  14 
  15 const int EXIT_SUCCESS = 0;
  16 const int EXIT_NO_MATCH = 1;
  17 const int EXIT_BAD_USAGE = -1;
  18 
  19 int main(int argc, char **argv)
  20 {
  21     char *flag = argv[1];
  22     if (!flag) {
  23         fprintf(stderr, "Usage: arg <flag> ...\n");
  24         return EXIT_BAD_USAGE;
  25     }
  26     size_t flaglen = strlen(flag);
  27     int ischarflag = flag[0] == '-' && flaglen == 2;
  28     for (int i = 2; i < argc; i++) {
  29         char *arg = argv[i];
  30         if (strncmp(arg, flag, flaglen) == 0) {
  31             if (arg[flaglen] == '\0') { // --flag ...
  32                 if (argv[i+1] && argv[i+1][0] != '-') // --flag <value>
  33                     puts(argv[i+1]); // value of the flag
  34                 return EXIT_SUCCESS;
  35             } else if (arg[flaglen] == '=') { // --flag=<value>
  36                 puts(&arg[flaglen+1]);
  37                 return EXIT_SUCCESS;
  38             }
  39         }
  40         if (ischarflag && arg[0] == '-' && arg[1] != '-') {
  41             // If flag is single-character, e.g. -f, look for it among other
  42             // single character flags like -xfy.
  43             for (char *c = &arg[1]; *c; c++) {
  44                 if (*c == flag[1])
  45                     return EXIT_SUCCESS;
  46             }
  47         }
  48     }
  49     return EXIT_NO_MATCH;
  50 }