How to use the command 'shopt' (with examples)

The ‘shopt’ command is used to manage Bash shell options, which are variables that control specific behavior within the Bash shell. These options are stored in the ‘$BASHOPTS’ environment variable.

Use case 1: List of all settable options and whether they are set

Code:

shopt

Motivation: This use case is helpful when you want to see a list of all the settable options and their current status. It allows you to quickly understand which options are enabled or disabled.

Explanation: The ‘shopt’ command without any arguments simply lists all the settable options and their current status. It does not make any changes to the options.

Example output:

cdable_vars              	off
cdspell                  	off
checkhash                	on
checkjobs                	off
cmdhist                  	on
compat31                 	off
compat32                 	off
compat40                 	off
compat41                 	off
compat42                 	off
compat43                 	off
compat44                 	off
compat45                 	off
compat46                 	off
compat47                 	off
compat_42                	on
compat_43                	on
complete_fullquote       	off

Use case 2: Set an option

Code:

shopt -s option_name

Motivation: This use case is useful when you want to enable a specific option. Enabling an option can change the behavior of the Bash shell and provide additional functionality.

Explanation: The ‘-s’ option is used to enable a specific option. Replace ‘option_name’ with the name of the option you want to enable.

Example:

shopt -s extglob

This command enables the ’extglob’ option, which allows the use of extended pattern matching features in filename expansion.

Use case 3: Unset an option

Code:

shopt -u option_name

Motivation: This use case is helpful when you want to disable a specific option. Disabling an option can revert the behavior of the Bash shell to its default settings.

Explanation: The ‘-u’ option is used to unset or disable a specific option. Replace ‘option_name’ with the name of the option you want to disable.

Example:

shopt -u nocaseglob

This command disables the ’nocaseglob’ option, which makes filename expansion case-sensitive.

Use case 4: Print a list of all options and their status formatted as runnable shopt commands

Code:

shopt -p

Motivation: This use case is useful when you want to see a list of all the options and their current status in a format that can be easily executed as ‘shopt’ commands. It allows you to quickly copy and paste the commands for specific options.

Explanation: The ‘-p’ option is used to print a list of all options and their status in the format of ‘shopt’ commands. Each line represents a ‘shopt’ command that can be executed to set or unset the corresponding option.

Example output:

shopt -s cdable_vars
shopt -u cdspell
shopt -s checkhash
shopt -u checkjobs
shopt -s cmdhist
shopt -u compat31
shopt -u compat32
shopt -u compat40
shopt -u compat41
shopt -u compat42
shopt -u compat43
shopt -u compat44
shopt -u compat45
shopt -u compat46
shopt -u compat47
shopt -s compat_42
shopt -s compat_43
shopt -u complete_fullquote

Use case 5: Show help for the command

Code:

help shopt

Motivation: This use case is helpful when you want to get more information about the ‘shopt’ command and its usage. The help command provides a brief description and examples of how to use the ‘shopt’ command effectively.

Explanation: The ‘help’ command followed by the name of the command you want help for is used to display the help documentation for that command.

Example output:

shopt: shopt [-pqsu] [-o] [optname...]
    Set and unset shell options.

    Change the value of shell attributes and optional behavior.  With no
    options, or with the -p option, a list of settable options is displayed,
    with an indication of whether or not each is set.  The -p option causes
...

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