getopt

Syntax

#include <unistd.h> int getopt(int argc, char * const *argv, const char *options); extern char *optarg; extern int optind, opterr, optopt;

Description

Parse options from the command line. options is a string of valid option characters. If a given option takes an argument, that character should be followed by a colon.

For each valid switch, this function sets optarg to the argument (if the switch takes one), sets optind to the index in argv that it is using, sets optopt to the option letter found, and returns the option letter found.

If an unexpected option is found, a question mark (`?') is returned. If an option argument is missing, a colon (`:') is returned if the first character in options is a colon, otherwise a question mark is returned. In both cases, if opterr is nonzero and the first character in options is not a colon, an error message is printed to stderr.

The example below shows how `?' can still be used as an option (e.g., to request a summary of program usage) in addition to flagging an unexpected option and a missing argument.

Return Value

The option character is returned when found. -1 is returned when there are no more options. A colon (`:') is returned when an option argument is missing and the first character in options is a colon. A question mark (`?') is returned when an invalid option is found or an option argument is missing and the first character in options is not a colon.

Portability

ANSI/ISO C	No
POSIX	1003.2-1992; 1003.1-2001

Example

int c; opterr = 0; while ((c=getopt(argc, argv, ":?vbf:")) != -1) { switch (c) { case 'v': verbose_flag ++; break; case 'b': binary_flag ++; break; case 'f': output_filename = optarg; break; case ':': printf("Missing argument %c\n", optopt); usage(); exit(1); case '?': if (optopt == '?') { usage(); exit(0); } else { printf("Unknown option %c\n", optopt); usage(); exit(1); } } }