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What is getopts in linux?
getopts is a built-in Unix shell command for parsing command-line arguments. It is designed to process command line arguments that follow the POSIX Utility Syntax Guidelines, based on the C interface of getopt. The predecessor to getopts was the external program getopt by Unix System Laboratories.
How does Getopt work in Unix?
The optstring works in the following way: Every option letter followed by a colon expects an argument, which is stored in the variable OPTARG. If getopts was expecting an argument, but could not parse one, it prints an error. If it was not expecting one, OPTARG will be initialized to “”(an empty string).
What is ${ Optarg?
optarg indicates an optional parameter to a command line option. opterr can be set to 0 to prevent getopt() from printing error messages. optind is the index of the next element of the argument list to be process, and optopt is the command line option last matched.
When to use the optind variable in getopts?
OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG.
Do you have to have an optional argument in getopts?
Any “optional” option arguments must actually be required as far as getopts will know. Of course, an optional argument must be a part of the same argument to the script as the option it goes with. Otherwise an option -f with an optional argument and an option -a with a required argument can get confused:
How is getopts initialized each time it is invoked?
Each time it is invoked, getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked.
Do you have to decrement optind to find an option?
The only way to do this is to test whether the option and its argument are in the same argument to the script. If so, OPTARG is the argument to the option. Otherwise, OPTIND must be decremented by one. Of course, the option is now required to have an argument, meaning a character will be found when an option is missing an argument.