The Shopt builtin

This builtin allows you to change additional shell optional behavior.

Documentation page here.

Shopt Flags

shopt [-pqsu] [-o] [optname …]  

Toggle the values of settings controlling optional shell behavior.
The settings can be either those listed below, or, if the -o option is used, those available with the -o option to the set builtin command (see The Set Builtin).

With no options, or with the -p option, a list of all settable options
is displayed, with an indication of whether or not each is set; if
optnames are supplied, the output is restricted to those options.

• The -p option causes output to be displayed in a form that may be reused as input.

Other options have the following meanings:

• -s: Enable (set) each optname.
• -u: Disable (unset) each optname.

• -q: Suppresses normal output; the return status indicates whether the optname is set or unset.
  If multiple optname arguments are given with -q, the return status is zero if all optnames are enabled; non-zero otherwise.

• -o: Restricts the values of optname to be those defined for the -o option to the set builtin (see The Set Builtin).

---

If either -s or -u is used with no optname arguments, shopt shows
only those options which are set or unset, respectively.

Unless otherwise noted, the shopt options are disabled (off) by default.

The return status when listing options is zero if all optnames are enabled, non-zero otherwise.
When setting or unsetting options, the return status is zero unless an optname is not a valid shell option.

---

Default Values (for me)

The output of:

shopt | column

with a clean .bashrc:

Option	Value	Option	Value
autocd	off	globstar	off
assoc_expand_once	off	gnu_errfmt	off
cdable_vars	off	histappend	off
cdspell	off	histreedit	off
checkhash	off	histverify	off
checkjobs	off	hostcomplete	off
checkwinsize	on	huponexit	off
cmdhist	on	inherit_errexit	off
compat31	off	interactive_comments	on
compat32	off	lastpipe	off
compat40	off	lithist	off
compat41	off	localvar_inherit	off
compat42	off	localvar_unset	off
compat43	off	login_shell	on
compat44	off	mailwarn	off
complete_fullquote	on	no_empty_cmd_completion	off
direxpand	off	nocaseglob	off
dirspell	off	nocasematch	off
dotglob	off	nullglob	off
execfail	off	progcomp	on
expand_aliases	on	progcomp_alias	off
extdebug	off	promptvars	on
extglob	on	restricted_shell	off
extquote	on	shift_verbose	off
failglob	off	sourcepath	on
force_fignore	on	xpg_echo	off
globasciiranges	on

The List of shopt Options

List of the options for shopt can be found at man://bash 4574

• assoc_expand_once:

  • If set, the shell suppresses multiple evaluation
    of associative array subscripts during arithmetic expression evaluation, while executing builtins
    that can perform variable assignments, and while
    executing builtins that perform array dereferencing.

• autocd:

  • This option is only used by interactive shells.
  • If set, a command name that is the name of a directory
    is executed as if it were the argument to the cd command.

• cdable_vars:

  • If this is set, an argument to the cd builtin command
    that is not a directory is assumed to be the name of a variable whose value is the directory to change to.

• cdspell:

  • This option is only used by interactive shells.
  • 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 a character too many.
  • If a correction is found, the corrected path is printed, and the command proceeds.

• checkhash:

  • If this is set, Bash checks that a command found in the hash table exists before trying to execute it.
  • If a hashed command no longer exists, a normal path search is performed.

• 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 (see Job Control).
  • The shell always postpones exiting if any jobs are stopped.

• checkwinsize:

  • If set, Bash checks the window size after each external
    (non-builtin) command and, if necessary, updates the
    values of LINES and COLUMNS.
  • This option is enabled by default.

• cmdhist:

  • If set, Bash attempts to save all lines of a multiple-line
    command in the same history entry.
  • This allows easy re-editing of multi-line commands.
  • This option is enabled by default, but only has an effect if
    command history is enabled (see Bash History Facilities).

• compat{num}:

  • compat31
  • compat32
  • compat40
  • compat41
  • compat42
  • compat43
  • compat44
  • These control aspects of the shell’s compatibility mode (see Shell Compatibility Mode).

• complete_fullquote:

  • This variable is set by default, which is the default Bash behavior in versions through 4.2.

  • If set, Bash quotes all shell metacharacters in filenames
    and directory names when performing completion.

  • If not set, Bash removes metacharacters such as the dollar sign from the set of characters that will be quoted in completed
    filenames when these metacharacters appear in shell variable references in words to be completed.

  • This means that dollar signs in variable names that expand to directories will not be quoted; however, any dollar signs
    appearing in filenames will not be quoted, either.

  • This is active only when bash is using backslashes to quote
    completed filenames.

• direxpand:

  • If set, Bash replaces directory names with the results of word expansion when performing filename completion.
  • This changes the contents of the Readline editing buffer.
  • If not set, Bash attempts to preserve what the user typed.

• dirspell:

  • If set, Bash attempts spelling correction on directory names
    during word completion if the directory name initially supplied
    does not exist.

• dotglob:

  • If set, Bash includes filenames beginning with a . in the results of filename expansion.
  • The filenames . and .. must always be matched explicitly, even if dotglob is set.

• execfail:

  • If this is set, a non-interactive shell will not exit if it cannot
    execute the file specified as an argument to the exec builtin command.
  • An interactive shell does not exit if exec fails.

• expand_aliases:

  • This option is enabled by default for interactive shells.
  • If set, aliases are expanded as described below under Aliases, Aliases.

• extdebug:

  • If set at shell invocation, or in a shell startup file, arrange
    to execute the debugger profile before the shell starts, identical to the --debugger option.

• If set after invocation, behavior intended for use by debuggers is enabled:

  • The -F option to the declare builtin (see Bash Builtin Commands)
    displays the source file name and line number corresponding to
    each function name supplied as an argument.

  • If the command run by the DEBUG trap returns a non-zero value, the next command is skipped and not executed.

  • If the command run by the DEBUG trap returns a value of 2, and the
    shell is executing in a subroutine (a shell function or a shell
    script executed by the . or source builtins), the
    shell simulates a call to return.

  • BASH_ARGC and BASH_ARGV are updated as described in their descriptions (see Bash Variables).
  • Function tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the DEBUG and RETURN traps.
  • Error tracing is enabled: command substitution, shell functions, and subshells invoked with ( command ) inherit the ERR trap.

• extglob:

  • If set, the extended pattern matching features described above (see Pattern Matching) are enabled.

• extquote:

  • This option is enabled by default.
  • If set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed in double quotes.

• failglob:

  • If set, patterns which fail to match filenames during filename
    expansion result in an expansion error.

• force_fignore:

  • This option is enabled by default.
  • If set, the suffixes specified by the FIGNORE shell
    variable cause words to be ignored when performing word completion even if the ignored words are the only possible completions.
    See Bash Variables, for a description of FIGNORE.

• globasciiranges:

  • If set, range expressions used in pattern matching bracket expressions (see Pattern Matching) behave as if in the traditional C locale when performing comparisons.
  • That is, the current locale's collating sequence is not taken into account, so b will not collate between A and B, and
    upper-case and lower-case ASCII characters will collate together.

• globskipdots:

  • If set, filename expansion will never match the filenames . and .., even if the pattern begins
    with a .. This option is enabled by default.

• 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.

• gnu_errfmt:

  • If set, shell error messages are written in the standard GNU error message format.

• histappend:

  • If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits, rather than overwriting the file.

• histreedit:

  • If set, and Readline is being used, a user is given the opportunity to re-edit a failed history substitution.

• histverify:

  • If set, and Readline is being used, the results of history substitution are not immediately passed to the shell parser.
  • Instead, the resulting line is loaded into the Readline editing buffer, allowing further modification.

• hostcomplete:

  • This option is enabled by default.
  • If set, and Readline is being used, Bash will attempt to perform hostname completion when a word containing a @ is being completed (see Letting Readline Type For You).

• huponexit:

  • If set, Bash will send SIGHUP to all jobs when an interactive login shell exits (see Signals).

• inherit_errexit:

  • If set, command substitution inherits the value of the errexit
    option, instead of unsetting it in the subshell environment.
  • This option is enabled when POSIX mode is enabled.

• interactive_comments:

  • This option is enabled by default.
  • Allow a word beginning with # to cause that word and all
    remaining characters on that line to be ignored in an interactive shell.

• lastpipe:

  • If set, and job control is not active, the shell runs the
    last command of a pipeline not executed in the background
    in the current shell environment.

• lithist:

  • If enabled, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded
    newlines rather than using semicolon separators where possible.

• localvar_inherit:

  • If set, local variables inherit the value and attributes of
    a variable of the same name that exists at a previous scope
    before any new value is assigned.
  • The nameref attribute is not inherited.

• localvar_unset:

  • If set, calling unset on local variables in previous function
    scopes marks them so subsequent lookups find them unset until that function returns.
  • This is identical to the behavior of unsetting local variables at the current function scope.

• login_shell:

  • The shell sets this option if it is started as a login shell (see Invoking Bash).
  • The value may not be changed.

• mailwarn:

  • If set, and a file that Bash is checking for mail has been accessed
    since the last time it was checked, the message "The mail in mailfile has been read" is displayed.

• no_empty_cmd_completion:

  • If set, and Readline is being used, Bash will not attempt to search the PATH for possible completions when completion is attempted on an empty line.

• nocaseglob:

  • If set, Bash matches filenames in a case-insensitive fashion when performing filename expansion.

• nocasematch:

  • If set, Bash matches patterns in a case-insensitive fashion when performing
    matching while executing case or [[ conditional commands (see Conditional Constructs), when performing pattern substitution word expansions, or when filtering possible completions as part of programmable completion.

• noexpand_translation:

  • If set, Bash encloses the translated results of $"..." quoting in
    single quotes instead of double quotes.
  • If the string is not translated, this has no effect.

• nullglob:

  • If set, Bash allows filename patterns which match no files to expand to a null string, rather than themselves.

• patsub_replacement:

  • This option is enabled by default.
  • If set, Bash expands occurrences of ‘&’ in the replacement string
    of pattern substitution to the text matched by the pattern, as described above (see Shell Parameter Expansion).

• progcomp:

  • This option is enabled by default.
  • If set, the programmable completion facilities (see Programmable Completion) are enabled.

• progcomp_alias:

  • If set, and programmable completion is enabled, Bash
    treats a command name that doesn’t have any completions as a possible alias and attempts alias expansion.
  • If it has an alias, Bash attempts programmable completion using the command word resulting from the expanded alias.

• promptvars:

  • This option is enabled by default.
  • If set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal after being expanded as
    described below (see Controlling the Prompt).

• restricted_shell:

  • The shell sets this option if it is started in restricted mode (see The Restricted Shell).
  • The value may not be changed.
  • This is not reset when the startup files are executed, allowing the startup files to discover whether or not a shell is restricted.

• shift_verbose:

  • If this is set, the shift builtin prints an error message when the shift count exceeds the number of positional parameters.

• sourcepath:

  • If set, the . (source) builtin uses the value of PATH to find the directory containing the file supplied as an argument.
  • This option is enabled by default.

• varredir_close:

  • If set, the shell automatically closes file descriptors assigned using the {varname} redirection syntax (see Redirections) instead of leaving them open when the command completes.

• xpg_echo:

  • If set, the echo builtin expands backslash-escape sequences by default.