What is Optarg in shell?

The Optarg is a Variable that is used by getopt( ) funtion. Optarg is used as a optional parameter to a command line option. The getopt( ) function is used to parse a command line argument in main( ) method in other words getopt( ) is a command line parser.

Is Optarg a string?

optstring is a string containing the legitimate option characters. If such a character is followed by a colon, the option requires an argument, so getopt() places a pointer to the following text in the same argv-element, or the text of the following argv-element, in optarg.

How does get opt work?

The getopt() function parses the command-line arguments. Its arguments argc and argv are the argument count and array as passed to the main() function on program invocation. An element of argv that starts with ‘-‘ (and is not exactly “-” or “–“) is an option element.

How does getopts work in bash?

getopts is designed to run multiple times in your script, in a loop, for example. It processes one option per loop iteration. When there are no more options to be processed, getopts returns false, which automatically terminates a while loop. For this reason, getopts and while are frequently used together.

What is getopt in shell?

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.

Is Optarg a pointer?

You don’t ordinarily need to copy the optarg string, since it is a pointer into the original argv array, not into a static area that might be overwritten.

Can Optarg be null?

4 Answers. Your argument string does not have a : after the X (e.g. X:f) so optarg will always be null.

Is getopt portable?

First, they are not portable. getopt is part of the POSIX standard but not the C standard; getopt_long is not part of any standards. In addition, getopt may behave differently depending on whether GNU extension is enabled. Using these functions can be tricky.

Where is Optarg defined?

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.