What is getopts in shell script?

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.

What is the purpose of getopts command?

Description. The getopts command is a Korn/POSIX Shell built-in command that retrieves options and option-arguments from a list of parameters.

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 Optind in bash?

$OPTIND is the number of options found by getopts . As pauljohn32 mentions in the comments, strictly speaking, OPTIND gives the position of the next command line argument. From the GNU Bash Reference Manual: getopts optstring name [args] getopts is used by shell scripts to parse positional parameters.

What does colon mean in Getopts?

If a letter is followed by a colon, the option is expected to have an argument, or group of arguments, which must be separated from it by white space. Each time it is invoked, getopts places the next option in the shell variable name and the index of the next argument to be processed in the shell variable OPTIND.

What is $? In script?

$? is a special variable in shell that reads the exit status of the last command executed. After a function returns, $? gives the exit status of the last command executed in the function.

What means $? In bash?

$? Expands to the exit status of the most recently executed foreground pipeline. By convention an exit status of 0 means success, and non-zero return status means failure. Learn more about exit statuses on wikipedia.

How do you ignore a case in UNIX?

The key to that case-insensitive search is the use of the -iname option, which is only one character different from the -name option. The -iname option is what makes the search case-insensitive.

What is the use of getopts command?

On Unix-like operating systems, getopts is a builtin command of the Bash shell. It parses command options and arguments, such as those passed to a shell script. getopts is the bash version of another system tool, getopt.

How to use getopts with multiple options?

Using getopts, you can provide also more than one option at the time to your script, combining the flags when you launch it. For example, let’s see what happens when we try to call our scripts with both the l and h options: As we can observe, both the options got processed, in the order we provided them.

Does getopts run on POSIX?

So if you write a script using getopts, you can be sure that it runs on any system running bash in POSIX mode (e.g., set -o posix ). getopts parses short options, which are a single dash (” – “) and a letter or digit. Examples of short options are -2, -d, and -D. It can also parse short options in combination, for instance -2dD.

What is the difference between getopts and optstring?

If optstring starts with a colon (: ), the script must take care of generating error messages; otherwise, getopts generates error messages. The getopts builtin uses the OPTIND (option index) and OPTARG (option argument) variables to track and store option-related values. When a shell script starts, the value of OPTIND is 1.