Bash options | Notion

<aside> 💡 Options are settings that change shell or script behaviour. The set builtin command can be use to set options. There are two ways to set options either by set -o option-name or, in short form, set -option-abbrev ****. To disable **an option, use set +o option-name ****or set +option-abbrev ****. To enable option on a script on the command line use, set +o option-name script-name ****or ****set option-abbrev script-name

</aside>

Abbreviation	Name	Effect
`-B`	brace expansion	Enable brace expansion (default setting = on)
`+B`	brace expansion	Disable brace expansion
`-C`	noclobber	Prevent overwriting of files by redirection (but this may be overridden by `>
`-D`	(none)	List double-quoted strings prefixed by $, but do not execute commands in script
`-a`	allexport	Export all defined variables
`-b`	notify	Notify when jobs running in background terminate (not of much use in a script)
`-c …`	(none)	Read commands from ...
`checkjobs`		Informs user of any open jobs upon shell exit. Introduced in version 4 of Bash, and still "experimental." Usage: shopt -s checkjobs (Caution: may hang!)
`-e`	errexit	Abort script at first error, when a command exits with non-zero status (except in until or while loops, if-tests, list constructs)
`-f`	noglob	Disable filename expansion (globbing)
`globstar`	globbing star-match	Enables the `*` globbing operator. Usage:* `shopt -s globstar`
`-i`	interactive	Runs a script in interactive mode
`-n`	noexec	Read commands in script, but do not execute them (syntax check)
`-o Option-Name`	(none)	Invoke the `Option-Name` option
`-o posix`	POSIX	Change the behavior of Bash, or invoked script, to conform to POSIX standard.
`-o pipefail`	pipe failure	Causes a pipeline to return the exit status of the last command in the pipe that returned a non-zero return value.
`-p`	privileged	Script runs as "suid" (caution!)
`-r`	restricted	Script runs in restricted mode
`-s`	stdin	Read commands from stdin
`-t`	onecmd	Exit after first command
`-u`	nounset	Attempt to use undefined variable outputs error message, and forces an exit
`-v`	verbose	Print each command to stdout before executing it
`-x`	xtrace	Similar to -v, but expands commands
`-`	(none)	End of options flag. All other arguments are positional parameters.
`--`	(none)	Unset positional parameters. If arguments given (-- arg1 arg2), positional parameters set to arguments.

<aside> 💡 Read more about bash options

More about bash options here

</aside>

Additional bash options

Description

<aside> 💡 The shopt builtin command allows you to change additional shell optional behavior.

</aside>

shopt options

Option	Description
`-o`	Restrict the values of `<OPTNAME…>` to only those also known by the set builtin
`-p`	Print all shell options and their current value. Default.
`-q`	Quiet mode. Set exit code if named option is set. For multiple options: `TRUE` if all options are set, `FALSE` otherwise
`-s`	Enable (set) the shell options named by `<OPTNAME…>` or list all enabled options if no names are given
`-u`	Disabe (unset) the shell options named by `<OPTNAME…>` or list all disabled options
if no names are given

shopt syntax

<aside> 🛠 shopt [-pqsu] [-o] <OPTNAME...>

</aside>

<aside> 💡 According to the option table, if only -s or -u are specified without any option names, only the currently enabled (-s) or disabled (-u) options are printed.

</aside>

Exit code

<aside> 💡 When listing options, the exit code is TRUE (0), if all options are enabled, FALSE otherwise.

When setting/unsetting an option, the exit code is TRUE unless the named option doesn't exitst.

</aside>

shopt -s nullglob  #Example to enable nullglob option

List of additional shell options

Option name	Description
`autocd`	If set, a command name that is the name of a directory is executed as if it were the argument to the cd command.
`cdspell`	If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correction is found, the corrected file name is printed, and the command proceeds.
`checkjobs`	If set, Bash lists the status of any stopped and running jobs before exiting an interactive shell. If any jobs are running, this causes the exit to be deferred until a second exit is attempted without an intervening command. The shell always postpones exiting if any jobs are stopped.
`dirspell`	If set, Bash will perform spelling corrections on directory names to match a glob.
`dotglob`	If set, Bash includes filenames beginning with a `.` (dot) in the results of pathname expansion.
`nullglob`	If set, Bash allows filename patterns which match no files to expand to a null string, rather than themselves.
`failglob`	If set, patterns which fail to match filenames during filename expansion result in an expansion error.
`nocaseglob`	If set, Bash matches filenames in a case-insensitive fashion when performing filename expansion.
`globstar`	If set, the pattern ‘**’ used in a filename expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a ‘/’, only directories and subdirectories match.

<aside> 💡 Here is an exhaustive lists of all the additional options

</aside>