of @cite{The GNU Bash Reference Manual},
for @code{Bash}, Version @value{VERSION}.
-Copyright @copyright{} 1988--2021 Free Software Foundation, Inc.
+Copyright @copyright{} 1988--2023 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
@subsubsection ANSI-C Quoting
@cindex quoting, ANSI
-Character sequences of the form $'@var{string}' are treated as a special
-kind of single quotes.
+Character sequences of the form @code{$'@var{string}'} are treated as
+a special kind of single quotes.
The sequence expands to @var{string}, with backslash-escaped characters
in @var{string} replaced as specified by the ANSI C standard.
Backslash escape sequences, if present, are decoded as follows:
@cindex internationalization
@cindex native languages
@cindex translation, native languages
+@menu
+* Creating Internationalized Scripts:: How to use translations and different
+ languages in your scripts.
+@end menu
-A double-quoted string preceded by a dollar sign (@samp{$})
+Prefixing a double-quoted string with a dollar sign (@samp{$}), such
+as @verb{|$"hello, world"|},
will cause the string to be translated according to the current locale.
-The @code{gettext} infrastructure performs the message catalog lookup and
-translation, using the @code{LC_MESSAGES} and @code{TEXTDOMAIN} shell
-variables, as explained below. See the gettext documentation for additional
-details.
+The @code{gettext} infrastructure performs the lookup and
+translation, using the @code{LC_MESSAGES}, @code{TEXTDOMAINDIR},
+and @code{TEXTDOMAIN} shell variables, as explained below.
+See the gettext documentation for additional details not covered here.
If the current locale is @code{C} or @code{POSIX},
-or if there are no translations available,
+if there are no translations available,
+of if the string is not translated,
the dollar sign is ignored.
-If the string is translated and replaced, the replacement is
-double-quoted.
+Since this is a form of double quoting, the string remains double-quoted
+by default, whether or not it is translated and replaced.
+If the @code{noexpand_translation} option is enabled
+using the @code{shopt} builtin (@pxref{The Shopt Builtin}),
+translated strings are single-quoted instead of double-quoted.
+
+The rest of this section is a brief overview of how you use gettext to
+create translations for strings in a shell script named @var{scriptname}.
+There are more details in the gettext documentation.
+
+@node Creating Internationalized Scripts
+@cindex internationalized scripts
+@cindex string translations
+Once you've marked the strings in your script
+that you want to translate using $"...",
+you create a gettext "template" file using the command
+
+@example
+bash --dump-po-strings @var{scriptname} > @var{domain}.pot
+@end example
+
+@noindent
+The @var{domain} is your @dfn{message domain}.
+It's just an arbitrary string that's used to identify the files gettext
+needs, like a package or script name.
+It needs to be unique among all
+the message domains on systems where you install the translations, so
+gettext knows which translations correspond to your script.
+You'll use the template file to create translations for each target language.
+The template file conventionally has the suffix @samp{.pot}.
+
+You copy this template file to a separate file for each target language
+you want to support (called "PO" files, which use the suffix @samp{.po}).
+PO files use various naming conventions, but
+when you are working to translate a template file into a particular
+language, you first copy the template file to a file whose name is the
+language you want to target, with the @samp{.po} suffix.
+For instance, the Spanish translations of your strings would be
+in a file named @samp{es.po}, and to get started using a message
+domain named "example," you would run
+
+@example
+cp example.pot es.po
+@end example
+
+@noindent
+Ultimately, PO files are often named @var{domain}.po and installed in
+directories that contain multiple translation files for a particular language.
+
+Whichever naming convention you choose, you will need to translate the
+strings in the PO files into the appropriate languages.
+This has to be done manually.
+
+When you have the translations and PO files complete, you'll use the
+gettext tools to produce what are called "MO" files, which are compiled
+versions of the PO files the gettext tools use to look up translations
+efficiently.
+MO files are also called "message catalog" files.
+You use the @command{msgfmt} program to do this.
+For instance, if you had a file with Spanish translations, you could run
+@example
+msgfmt -o es.mo es.po
+@end example
+
+@noindent
+to produce the corresponding MO file.
+
+Once you have the MO files, you decide where to install them and use the
+@code{TEXTDOMAINDIR} shell variable to tell the gettext tools where they are.
+Make sure to use the same message domain to name the MO files
+as you did for the PO files when you install them.
+
+@vindex LANG
@vindex LC_MESSAGES
@vindex TEXTDOMAIN
@vindex TEXTDOMAINDIR
-Some systems use the message catalog selected by the @env{LC_MESSAGES}
-shell variable. Others create the name of the message catalog from the
-value of the @env{TEXTDOMAIN} shell variable, possibly adding a
-suffix of @samp{.mo}. If you use the @env{TEXTDOMAIN} variable, you
-may need to set the @env{TEXTDOMAINDIR} variable to the location of
-the message catalog files. Still others use both variables in this
-fashion:
-@env{TEXTDOMAINDIR}/@env{LC_MESSAGES}/LC_MESSAGES/@env{TEXTDOMAIN}.mo.
+Your users will use the @env{LANG} or @env{LC_MESSAGES} shell variables to
+select the desired language.
+
+You set the @env{TEXTDOMAIN} variable to the script's message domain.
+As above, you use the message domain to name your translation files.
+
+You, or possibly your users, set the @env{TEXTDOMAINDIR} variable to the
+name of a directory where the message catalog files are stored.
+If you install the message files into the system's standard message catalog
+directory, you don't need to worry about this variable.
+
+The directory where the message catalog files are stored varies between
+systems.
+Some use the message catalog selected by the @env{LC_MESSAGES}
+shell variable.
+Others create the name of the message catalog from the value of the
+@env{TEXTDOMAIN} shell variable, possibly adding the @samp{.mo} suffix.
+If you use the @env{TEXTDOMAIN} variable, you may need to set the
+@env{TEXTDOMAINDIR} variable to the location of the message catalog files,
+as above.
+It's common to use both variables in this fashion:
+@env{$TEXTDOMAINDIR}/@env{$LC_MESSAGES}/LC_MESSAGES/@env{$TEXTDOMAIN}.mo.
+
+If you used that last convention, and you wanted to store the message
+catalog files with Spanish (es) and Esperanto (eo) translations into a
+local directory you use for custom translation files, you could run
+
+@example
+TEXTDOMAIN=example
+TEXTDOMAINDIR=/usr/local/share/locale
+
+cp es.mo $@{TEXTDOMAINDIR@}/es/LC_MESSAGES/$@{TEXTDOMAIN@}.mo
+cp eo.mo $@{TEXTDOMAINDIR@}/eo/LC_MESSAGES/$@{TEXTDOMAIN@}.mo
+@end example
+
+When all of this is done, and the message catalog files containing the
+compiled translations are installed in the correct location,
+your users will be able to see translated strings
+in any of the supported languages by setting the @env{LANG} or
+@env{LC_MESSAGES} environment variables before running your script.
@node Comments
@subsection Comments
When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}), @code{time}
may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children.
-The @env{TIMEFORMAT} variable may be used to specify the format of
-the time information.
+The @env{TIMEFORMAT} variable specifies the format of the time information.
If the pipeline is not executed asynchronously (@pxref{Lists}), the
shell waits for all commands in the pipeline to complete.
-Each command in a pipeline is executed in its own subshell, which is a
+Each command in a multi-command pipeline,
+where pipes are created,
+is executed in its own @dfn{subshell}, which is a
separate process (@pxref{Command Execution Environment}).
If the @code{lastpipe} option is enabled using the @code{shopt} builtin
(@pxref{The Shopt Builtin}),
The @var{word} undergoes tilde expansion, parameter expansion, command
substitution, arithmetic expansion, and quote removal
(@pxref{Shell Parameter Expansion})
-before matching is
-attempted. Each @var{pattern} undergoes tilde expansion, parameter
-expansion, command substitution, and arithmetic expansion.
+before matching is attempted.
+Each @var{pattern} undergoes tilde expansion, parameter expansion,
+command substitution, arithmetic expansion, process substitution, and
+quote removal.
There may be an arbitrary number of @code{case} clauses, each terminated
by a @samp{;;}, @samp{;&}, or @samp{;;&}.
@end example
The list of words following @code{in} is expanded, generating a list
-of items. The set of expanded words is printed on the standard
+of items, and the set of expanded words is printed on the standard
error output stream, each preceded by a number. If the
@samp{in @var{words}} is omitted, the positional parameters are printed,
as if @samp{in "$@@"} had been specified.
-The @env{PS3} prompt is then displayed and a line is read from the
-standard input.
+@code{select} then displays the @env{PS3}
+prompt and reads a line from the standard input.
If the line consists of a number corresponding to one of the displayed
words, then the value of @var{name} is set to that word.
If the line is empty, the words and prompt are displayed again.
-If @code{EOF} is read, the @code{select} command completes.
+If @code{EOF} is read, the @code{select} command completes and returns 1.
Any other value read causes @var{name} to be set to null.
The line read is saved in the variable @env{REPLY}.
The arithmetic @var{expression} is evaluated according to the rules
described below (@pxref{Shell Arithmetic}).
+The @var{expression} undergoes the same expansions
+as if it were within double quotes,
+but double quote characters in @var{expression} are not treated specially
+are removed.
If the value of the expression is non-zero, the return status is 0;
-otherwise the return status is 1. This is exactly equivalent to
-@example
-let "@var{expression}"
-@end example
-@noindent
-@xref{Bash Builtins}, for a full description of the @code{let} builtin.
+otherwise the return status is 1.
+
@item [[@dots{}]]
@rwindex [[
the conditional expression @var{expression}.
Expressions are composed of the primaries described below in
@ref{Bash Conditional Expressions}.
-Word splitting and filename expansion are not performed on the words
-between the @code{[[} and @code{]]}; tilde expansion, parameter and
+The words between the @code{[[} and @code{]]} do not undergo word splitting
+and filename expansion.
+The shell performs tilde expansion, parameter and
variable expansion, arithmetic expansion, command substitution, process
-substitution, and quote removal are performed.
+substitution, and quote removal on those words
+(the expansions that would occur if the words were enclosed in double quotes).
Conditional operators such as @samp{-f} must be unquoted to be recognized
as primaries.
The element of @code{BASH_REMATCH} with index @var{n} is the portion of the
string matching the @var{n}th parenthesized subexpression.
+Bash sets
+@code{BASH_REMATCH}
+in the global scope; declaring it as a local variable will lead to
+unexpected results.
+
Expressions may be combined using the following operators, listed
in decreasing order of precedence:
( @var{list} )
@end example
-Placing a list of commands between parentheses causes a subshell
-environment to be created (@pxref{Command Execution Environment}), and each
-of the commands in @var{list} to be executed in that subshell. Since the
-@var{list} is executed in a subshell, variable assignments do not remain in
-effect after the subshell completes.
+Placing a list of commands between parentheses forces the shell to create
+a subshell (@pxref{Command Execution Environment}), and each
+of the commands in @var{list} is executed in that subshell environment.
+Since the @var{list} is executed in a subshell, variable assignments do not
+remain in effect after the subshell completes.
@item @{@}
@rwindex @{
the input source, and so on). Parallel can replace @code{xargs} or feed
commands from its input sources to several different instances of Bash.
-For a complete description, refer to the GNU Parallel documentation. A few
-examples should provide a brief introduction to its use.
-
-For example, it is easy to replace @code{xargs} to gzip all html files in the
-current directory and its subdirectories:
-@example
-find . -type f -name '*.html' -print | parallel gzip
-@end example
-@noindent
-If you need to protect special characters such as newlines in file names,
-use find's @option{-print0} option and parallel's @option{-0} option.
-
-You can use Parallel to move files from the current directory when the
-number of files is too large to process with one @code{mv} invocation:
-@example
-printf '%s\n' * | parallel mv @{@} destdir
-@end example
-
-As you can see, the @{@} is replaced with each line read from standard input.
-While using @code{ls} will work in most instances, it is not sufficient to
-deal with all filenames. @code{printf} is a shell builtin, and therefore is
-not subject to the kernel's limit on the number of arguments to a program,
-so you can use @samp{*} (but see below about the @code{dotglob} shell option).
-If you need to accommodate special characters in filenames, you can use
-
-@example
-printf '%s\0' * | parallel -0 mv @{@} destdir
-@end example
-
-@noindent
-as alluded to above.
-
-This will run as many @code{mv} commands as there are files in the current
-directory.
-You can emulate a parallel @code{xargs} by adding the @option{-X} option:
-@example
-printf '%s\0' * | parallel -0 -X mv @{@} destdir
-@end example
-
-(You may have to modify the pattern if you have the @code{dotglob} option
-enabled.)
-
-GNU Parallel can replace certain common idioms that operate on lines read
-from a file (in this case, filenames listed one per line):
-@example
- while IFS= read -r x; do
- do-something1 "$x" "config-$x"
- do-something2 < "$x"
- done < file | process-output
-@end example
-
-@noindent
-with a more compact syntax reminiscent of lambdas:
-@example
-cat list | parallel "do-something1 @{@} config-@{@} ; do-something2 < @{@}" |
- process-output
-@end example
-
-Parallel provides a built-in mechanism to remove filename extensions, which
-lends itself to batch file transformations or renaming:
-@example
-ls *.gz | parallel -j+0 "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}"
-@end example
-@noindent
-This will recompress all files in the current directory with names ending
-in .gz using bzip2, running one job per CPU (-j+0) in parallel.
-(We use @code{ls} for brevity here; using @code{find} as above is more
-robust in the face of filenames containing unexpected characters.)
-Parallel can take arguments from the command line; the above can also be
-written as
-
-@example
-parallel "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}" ::: *.gz
-@end example
-
-If a command generates output, you may want to preserve the input order in
-the output. For instance, the following command
-@example
-@{
- echo foss.org.my ;
- echo debian.org ;
- echo freenetproject.org ;
-@} | parallel traceroute
-@end example
-@noindent
-will display as output the traceroute invocation that finishes first.
-Adding the @option{-k} option
-@example
-@{
- echo foss.org.my ;
- echo debian.org ;
- echo freenetproject.org ;
-@} | parallel -k traceroute
-@end example
-@noindent
-will ensure that the output of @code{traceroute foss.org.my} is displayed first.
-
-Finally, Parallel can be used to run a sequence of shell commands in parallel,
-similar to @samp{cat file | bash}.
-It is not uncommon to take a list of filenames, create a series of shell
-commands to operate on them, and feed that list of commands to a shell.
-Parallel can speed this up. Assuming that @file{file} contains a list of
-shell commands, one per line,
-
-@example
-parallel -j 10 < file
-@end example
-
-@noindent
-will evaluate the commands using the shell (since no explicit command is
-supplied as an argument), in blocks of ten shell jobs at a time.
+For a complete description, refer to the GNU Parallel documentation, which
+is available at
+@url{https://www.gnu.org/software/parallel/parallel_tutorial.html}.
@node Shell Functions
@section Shell Functions
before the @code{return}.
Variables local to the function may be declared with the
-@code{local} builtin. These variables are visible only to
+@code{local} builtin (@dfn{local variables}).
+Ordinarily, variables and their values
+are shared between a function and its caller.
+These variables are visible only to
the function and the commands it invokes. This is particularly
important when a shell function calls other functions.
+In the following description, the @dfn{current scope} is a currently-
+executing function.
+Previous scopes consist of that function's caller and so on,
+back to the "global" scope, where the shell is not executing
+any shell function.
+Consequently, a local variable at the current local scope is a variable
+declared using the @code{local} or @code{declare} builtins in the
+function that is currently executing.
+
Local variables "shadow" variables with the same name declared at
previous scopes. For instance, a local variable declared in a function
hides a global variable of the same name: references and assignments
otherwise the unset will refer to the variable found in any calling scope
as described above.
If a variable at the current local scope is unset, it will remain so
+(appearing as unset)
until it is reset in that scope or until the function returns.
Once the function returns, any instance of the variable at a previous
scope will become visible.
If the unset acts on a variable at a previous scope, any instance of a
-variable with that name that had been shadowed will become visible.
+variable with that name that had been shadowed will become visible
+(see below how @code{localvar_unset}shell option changes this behavior).
Function names and definitions may be listed with the
@option{-f} option to the @code{declare} (@code{typeset})
will list the function names only
(and optionally the source file and line number, if the @code{extdebug}
shell option is enabled).
-Functions may be exported so that subshells
+Functions may be exported so that child shell processes
+(those created when executing a separate shell invocation)
automatically have them defined with the
@option{-f} option to the @code{export} builtin
(@pxref{Bourne Shell Builtins}).
is not given, the variable is assigned the null string. All
@var{value}s undergo tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, and quote
-removal (detailed below). If the variable has its @code{integer}
+removal (@pxref{Shell Parameter Expansion}).
+If the variable has its @code{integer}
attribute set, then @var{value}
is evaluated as an arithmetic expression even if the @code{$((@dots{}))}
expansion is not used (@pxref{Arithmetic Expansion}).
-Word splitting is not performed, with the exception
-of @code{"$@@"} as explained below.
-Filename expansion is not performed.
+Word splitting and filename expansion are not performed.
Assignment statements may also appear as arguments to the
@code{alias},
@code{declare}, @code{typeset}, @code{export}, @code{readonly},
@item $
@vindex $$
-($$) Expands to the process @sc{id} of the shell. In a @code{()} subshell, it
+($$) Expands to the process @sc{id} of the shell. In a subshell, it
expands to the process @sc{id} of the invoking shell, not the subshell.
@item !
After these expansions are performed, quote characters present in the
original word are removed unless they have been quoted themselves
-(@dfn{quote removal}).
+(@dfn{quote removal}). @xref{Quote Removal} for more details.
Only brace expansion, word splitting, and filename expansion
can increase the number of words of the expansion; other expansions
@code{"$@{@var{name}[@@]@}"} and @code{$@{@var{name}[*]@}}
(@pxref{Arrays}).
-After all expansions, @code{quote removal} (@pxref{Quote Removal})
-is performed.
-
@node Brace Expansion
@subsection Brace Expansion
@cindex brace expansion
@end example
A sequence expression takes the form @code{@{@var{x}..@var{y}[..@var{incr}]@}},
-where @var{x} and @var{y} are either integers or single characters,
+where @var{x} and @var{y} are either integers or letters,
and @var{incr}, an optional increment, is an integer.
When integers are supplied, the expression expands to each number between
@var{x} and @var{y}, inclusive.
When either @var{x} or @var{y} begins with a zero, the shell
attempts to force all generated terms to contain the same number of digits,
zero-padding where necessary.
-When characters are supplied, the expression expands to each character
+When letters are supplied, the expression expands to each character
lexicographically between @var{x} and @var{y}, inclusive,
using the default C locale.
-Note that both @var{x} and @var{y} must be of the same type.
+Note that both @var{x} and @var{y} must be of the same type
+(integer or letter).
When the increment is supplied, it is used as the difference between
each term. The default increment is 1 or -1 as appropriate.
In each of the cases below, @var{word} is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
-When not performing substring expansion, using the form described
+When not performing substring expansion, using the forms described
below (e.g., @samp{:-}), Bash tests for a parameter that is unset or null.
Omitting the colon results in a test only for a parameter that is unset.
Put another way, if the colon is included,
@var{word} is substituted. Otherwise, the value of
@var{parameter} is substituted.
+@example
+$ v=123
+$ echo $@{v-unset@}
+123
+$ echo $@{v:-unset-or-null@}
+123
+$ unset v
+$ echo $@{v-unset@}
+unset
+$ v=
+$ echo $@{v:-unset-or-null@}
+unset-or-null
+@end example
+
@item $@{@var{parameter}:=@var{word}@}
If @var{parameter}
is unset or null, the expansion of @var{word}
Positional parameters and special parameters may not be assigned to
in this way.
+@example
+$ var=
+$ : $@{var:=DEFAULT@}
+$ echo $var
+DEFAULT
+@end example
+
@item $@{@var{parameter}:?@var{word}@}
If @var{parameter}
is null or unset, the expansion of @var{word} (or a message
is not interactive, exits. Otherwise, the value of @var{parameter} is
substituted.
+@example
+$ var=
+$ : $@{var:?var is unset or null@}
+bash: var: var is unset or null
+@end example
+
@item $@{@var{parameter}:+@var{word}@}
If @var{parameter}
is null or unset, nothing is substituted, otherwise the expansion of
@var{word} is substituted.
+@example
+$ var=123
+$ echo $@{var:+var is set and not null@}
+var is set and not null
+@end example
+
@item $@{@var{parameter}:@var{offset}@}
@itemx $@{@var{parameter}:@var{offset}:@var{length}@}
This is referred to as Substring Expansion.
It expands to up to @var{length} characters of the value of @var{parameter}
starting at the character specified by @var{offset}.
-If @var{parameter} is @samp{@@}, an indexed array subscripted by
+If @var{parameter} is @samp{@@} or @samp{*}, an indexed array subscripted by
@samp{@@} or @samp{*}, or an associative array name, the results differ as
described below.
If @var{length} is omitted, it expands to the substring of the value of
bcdef
@end verbatim
-If @var{parameter} is @samp{@@}, the result is @var{length} positional
-parameters beginning at @var{offset}.
+If @var{parameter} is @samp{@@} or @samp{*}, the result is @var{length}
+positional parameters beginning at @var{offset}.
A negative @var{offset} is taken relative to one greater than the greatest
positional parameter, so an offset of -1 evaluates to the last positional
-parameter.
+parameter (or 0 if there are no positional parameters).
It is an expansion error if @var{length} evaluates to a number less than zero.
The following examples illustrate substring expansion using positional
array in turn, and the expansion is the resultant list.
@item $@{@var{parameter}/@var{pattern}/@var{string}@}
-
+@itemx $@{@var{parameter}//@var{pattern}/@var{string}@}
+@itemx $@{@var{parameter}/#@var{pattern}/@var{string}@}
+@itemx $@{@var{parameter}/%@var{pattern}/@var{string}@}
The @var{pattern} is expanded to produce a pattern just as in
filename expansion.
@var{Parameter} is expanded and the longest match of @var{pattern}
against its value is replaced with @var{string}.
+@var{string} undergoes tilde expansion, parameter and variable expansion,
+arithmetic expansion, command and process substitution, and quote removal.
The match is performed according to the rules described below
(@pxref{Pattern Matching}).
-If @var{pattern} begins with @samp{/}, all matches of @var{pattern} are
-replaced with @var{string}. Normally only the first match is replaced.
-If @var{pattern} begins with @samp{#}, it must match at the beginning
-of the expanded value of @var{parameter}.
-If @var{pattern} begins with @samp{%}, it must match at the end
-of the expanded value of @var{parameter}.
-If @var{string} is null, matches of @var{pattern} are deleted
+
+In the first form above, only the first match is replaced.
+If there are two slashes separating @var{parameter} and @var{pattern}
+(the second form above), all matches of @var{pattern} are
+replaced with @var{string}.
+If @var{pattern} is preceded by @samp{#} (the third form above),
+it must match at the beginning of the expanded value of @var{parameter}.
+If @var{pattern} is preceded by @samp{%} (the fourth form above),
+it must match at the end of the expanded value of @var{parameter}.
+If the expansion of @var{string} is null,
+matches of @var{pattern} are deleted.
+If @var{string} is null,
+matches of @var{pattern} are deleted
and the @samp{/} following @var{pattern} may be omitted.
+
+If the @code{patsub_replacement} shell option is enabled using @code{shopt},
+any unquoted instances of @samp{&} in @var{string} are replaced with the
+matching portion of @var{pattern}.
+This is intended to duplicate a common @code{sed} idiom.
+
+Quoting any part of @var{string} inhibits replacement in the
+expansion of the quoted portion, including replacement strings stored
+in shell variables.
+Backslash will escape @samp{&} in @var{string}; the backslash is removed
+in order to permit a literal @samp{&} in the replacement string.
+Users should take care if @var{string} is double-quoted to avoid
+unwanted interactions between the backslash and double-quoting, since
+backslash has special meaning within double quotes.
+Pattern substitution performs the check for unquoted @samp{&} after
+expanding @var{string},
+so users should ensure to properly quote any occurrences of @samp{&}
+they want to be taken literally in the replacement
+and ensure any instances of @samp{&} they want to be replaced are unquoted.
+
+For instance,
+
+@example
+var=abcdef
+rep='& '
+echo $@{var/abc/& @}
+echo "$@{var/abc/& @}"
+echo $@{var/abc/$rep@}
+echo "$@{var/abc/$rep@}"
+@end example
+
+@noindent
+will display four lines of "abc def", while
+
+@example
+var=abcdef
+rep='& '
+echo $@{var/abc/\& @}
+echo "$@{var/abc/\& @}"
+echo $@{var/abc/"& "@}
+echo $@{var/abc/"$rep"@}
+@end example
+
+@noindent
+will display four lines of "& def".
+Like the pattern removal operators, double quotes surrounding the
+replacement string quote the expanded characters, while double quotes
+enclosing the entire parameter substitution do not, since
+the expansion is performed in a
+context that doesn't take any enclosing double quotes into account.
+
+Since backslash can escape @samp{&}, it can also escape a backslash in
+the replacement string.
+This means that @samp{\\} will insert a literal
+backslash into the replacement, so these two @code{echo} commands
+
+@example
+var=abcdef
+rep='\\&xyz'
+echo $@{var/abc/\\&xyz@}
+echo $@{var/abc/$rep@}
+@end example
+
+@noindent
+will both output @samp{\abcxyzdef}.
+
+It should rarely be necessary to enclose only @var{string} in double
+quotes.
+
If the @code{nocasematch} shell option
(see the description of @code{shopt} in @ref{The Shopt Builtin})
is enabled, the match is performed without regard to the case
Each character in the expanded value of @var{parameter} is tested against
@var{pattern}, and, if it matches the pattern, its case is converted.
The pattern should not attempt to match more than one character.
+
The @samp{^} operator converts lowercase letters matching @var{pattern}
to uppercase; the @samp{,} operator converts matching uppercase letters
to lowercase.
the first character in the expanded value.
If @var{pattern} is omitted, it is treated like a @samp{?}, which matches
every character.
+
If @var{parameter} is @samp{@@} or @samp{*},
the case modification operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
@item a
The expansion is a string consisting of flag values representing
@var{parameter}'s attributes.
+@item k
+Like the @samp{K} transformation, but expands the keys and values of
+indexed and associative arrays to separate words after word splitting.
@end table
If @var{parameter} is @samp{@@} or @samp{*},
Command substitution allows the output of a command to replace
the command itself.
-Command substitution occurs when a command is enclosed as follows:
+The standard form of command substitution occurs when a command is
+enclosed as follows:
@example
$(@var{command})
@end example
@noindent
-or
+or (deprecated)
@example
-`@var{command}`
+`@var{command}`.
@end example
@noindent
-Bash performs the expansion by executing @var{command} in a subshell environment
-and replacing the command substitution with the standard output of the
-command, with any trailing newlines deleted.
+Bash performs command substitution by executing @var{command} in a subshell
+environment and replacing the command substitution with the standard
+output of the command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution @code{$(cat @var{file})} can be
replaced by the equivalent but faster @code{$(< @var{file})}.
-When the old-style backquote form of substitution is used,
+With the old-style backquote form of substitution,
backslash retains its literal meaning except when followed by
@samp{$}, @samp{`}, or @samp{\}.
The first backquote not preceded by a backslash terminates the
When using the @code{$(@var{command})} form, all characters between
the parentheses make up the command; none are treated specially.
+There is an alternate form of command substitution:
+
+@example
+$@{@var{c} @var{command}; @}
+@end example
+
+@noindent
+which executes @var{command} in the current execution environment
+and captures its output, again with trailing newlines removed.
+
+The character @var{c} following the open brace must be a space, tab,
+newline, or @samp{|}, and the close brace must be in a position
+where a reserved word may appear (i.e., preceded by a command terminator
+such as semicolon).
+Bash allows the close brace to be joined to the remaining characters in
+the word without being followed by a shell metacharacter as a reserved
+word would usually require.
+
+Any side effects of @var{command} take effect immediately
+in the current execution environment and persist in the current
+environment after the command completes (e.g., the @code{exit} builtin
+will exit the shell).
+
+This type of command substitution superficially resembles executing an
+unnamed shell function: local variables are created as when a shell
+function is executing, and the @code{return} builtin forces
+@var{command} to complete;
+however, the rest of the execution environment,
+including the positional parameters, is shared with the caller.
+
+If the first character following the open brace
+is a @samp{|}, the construct expands to the
+value of the @code{REPLY} shell variable after @var{command} executes,
+without removing any trailing newlines,
+and the standard output of @var{command} remains the same as in the
+calling shell.
+Bash creates @code{REPLY} as an initially-unset local variable when
+@var{command} executes, and restores @code{REPLY} to the value it had
+before the command substitution after @var{command} completes,
+as with any local variable.
+
+For example, this construct expands to @samp{12345}, and leaves the
+shell variable @code{X} unchanged in the current execution environment:
+
+@example
+
+$@{ local X=12345 ; echo $X; @}
+@end example
+
+@noindent
+(not declaring @code{X} as local would modify its value in the current
+environment, as with normal shell function execution),
+while this construct does not require any output to expand to
+@samp{12345}:
+
+@example
+$@{| REPLY=12345; @}
+@end example
+
+@noindent
+and restores @code{REPLY} to the value it had before the command substitution.
+
Command substitutions may be nested. To nest when using the backquoted
form, escape the inner backquotes with backslashes.
-If the substitution appears within double quotes, word splitting and
-filename expansion are not performed on the results.
+If the substitution appears within double quotes, Bash does not perform
+word splitting and filename expansion on the results.
@node Arithmetic Expansion
@subsection Arithmetic Expansion
$(( @var{expression} ))
@end example
-The @var{expression} is treated as if it were within double quotes, but
-a double quote inside the parentheses is not treated specially.
+The @var{expression} undergoes the same expansions
+as if it were within double quotes,
+but double quote characters in @var{expression} are not treated specially
+and are removed.
All tokens in the expression undergo parameter and variable expansion,
command substitution, and quote removal.
The result is treated as the arithmetic expression to be evaluated.
The shell treats each character of @env{$IFS} as a delimiter, and splits
the results of the other expansions into words using these characters
as field terminators.
+
If @env{IFS} is unset, or its value is exactly @code{<space><tab><newline>},
the default, then sequences of
-@code{ <space>}, @code{<tab>}, and @code{<newline>}
+@code{space}, @code{tab}, and @code{newline}
at the beginning and end of the results of the previous
expansions are ignored, and any sequence of @env{IFS}
characters not at the beginning or end serves to delimit words.
whitespace, along with any adjacent @env{IFS}
whitespace characters, delimits a field. A sequence of @env{IFS}
whitespace characters is also treated as a delimiter.
+
If the value of @env{IFS} is null, no word splitting occurs.
+If @env{IFS} is unset, word splitting behaves as if it contained
+the default value @code{<space><tab><newline>}.
Explicit null arguments (@code{""} or @code{''}) are retained
and passed to commands as empty strings.
When a pattern is used for filename expansion, the character @samp{.}
at the start of a filename or immediately following a slash
must be matched explicitly, unless the shell option @code{dotglob} is set.
-The filenames @samp{.} and @samp{..} must always be matched explicitly,
+In order to match the filenames @samp{.} and @samp{..},
+the pattern must begin with @samp{.} (for example, @samp{.?}),
even if @code{dotglob} is set.
-In other cases, the @samp{.} character is not treated specially.
+If the @code{globskipdots} shell option is enabled, the filenames
+@samp{.} and @samp{..} are never matched, even if the pattern begins
+with a @samp{.}.
+When not matching filenames, the @samp{.} character is not treated specially.
When matching a filename, the slash character must always be
matched explicitly by a slash in the pattern, but in other matching
See the description of @code{shopt} in @ref{The Shopt Builtin},
for a description of the @code{nocaseglob}, @code{nullglob},
+@code{globskipdots},
@code{failglob}, and @code{dotglob} options.
The @env{GLOBIGNORE}
The @code{dotglob} option is disabled when @env{GLOBIGNORE}
is unset.
+After the pattern is expanded and matched against filenames, the value of the
+@env{GLOBSORT} variable controls how the results are sorted, as described
+below (@pxref{Bash Variables}).
+
@node Pattern Matching
@subsubsection Pattern Matching
@cindex pattern matching
may be matched by including it as the first or last character
in the set. A @samp{]} may be matched by including it as the first
character in the set.
-The sorting order of characters in range expressions is determined by
+The sorting order of characters in range expressions,
+and the characters included in the range,
+are determined by
the current locale and the values of the
@env{LC_COLLATE} and @env{LC_ALL} shell variables, if set.
For example, in the default C locale, @samp{[a-dx-z]} is equivalent to
@samp{[abcdxyz]}. Many locales sort characters in dictionary order, and in
these locales @samp{[a-dx-z]} is typically not equivalent to @samp{[abcdxyz]};
-it might be equivalent to @samp{[aBbCcDdxXyYz]}, for example. To obtain
+it might be equivalent to @samp{[aBbCcDdxYyZz]}, for example. To obtain
the traditional interpretation of ranges in bracket expressions, you can
force the use of the C locale by setting the @env{LC_COLLATE} or
@env{LC_ALL} environment variable to the value @samp{C}, or enable the
@end table
If the @code{extglob} shell option is enabled using the @code{shopt}
-builtin, several extended pattern matching operators are recognized.
+builtin, the shell recognizes several extended pattern matching operators.
In the following description, a @var{pattern-list} is a list of one
or more patterns separated by a @samp{|}.
+When matching filenames, the @code{dotglob} shell option determines
+the set of filenames that are tested, as described above.
Composite patterns may be formed using one or more of the following
sub-patterns:
Matches anything except one of the given patterns.
@end table
+The @code{extglob} option changes the behavior of the parser, since the
+parentheses are normally treated as operators with syntactic meaning.
+To ensure that extended matching patterns are parsed correctly, make sure
+that @code{extglob} is enabled before parsing constructs containing the
+patterns, including shell functions and command substitutions.
+
+When matching filenames, the @code{dotglob} shell option determines
+the set of filenames that are tested:
+when @code{dotglob} is enabled, the set of filenames includes all files
+beginning with @samp{.}, but the filenames
+@samp{.} and @samp{..} must be matched by a
+pattern or sub-pattern that begins with a dot;
+when it is disabled, the set does not
+include any filenames beginning with ``.'' unless the pattern
+or sub-pattern begins with a @samp{.}.
+As above, @samp{.} only has a special meaning when matching filenames.
+
Complicated extended pattern matching against long strings is slow,
especially when the patterns contain alternations and the strings
contain multiple matches.
If @{@var{varname}@} is supplied, the redirection persists beyond
the scope of the command, allowing the shell programmer to manage
the file descriptor's lifetime manually.
+The @code{varredir_close} shell option manages this behavior
+(@pxref{The Shopt Builtin}).
In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
Bash handles several filenames specially when they are used in
redirections, as described in the following table.
If the operating system on which Bash is running provides these
-special files, bash will use them; otherwise it will emulate them
+special files, Bash will use them; otherwise it will emulate them
internally with the behavior described below.
@table @code
@subsection Here Documents
This type of redirection instructs the shell to read input from the
-current source until a line containing only @var{word}
-(with no trailing blanks) is seen. All of
-the lines read up to that point are then used as the standard
+current source until a line containing only @var{delimiter}
+(with no trailing blanks) is seen.
+All of the lines read up to that point are then used as the standard
input (or file descriptor @var{n} if @var{n} is specified) for a command.
The format of here-documents is:
No parameter and variable expansion, command substitution,
arithmetic expansion, or filename expansion is performed on
-@var{word}. If any part of @var{word} is quoted, the
+@var{word}.
+
+If any part of @var{word} is quoted, the
@var{delimiter} is the result of quote removal on @var{word},
and the lines in the here-document are not expanded.
If @var{word} is unquoted,
+@var{delimiter} is @var{word} itself,
all lines of the here-document are subjected to
parameter expansion, command substitution, and arithmetic expansion,
the character sequence @code{\newline} is ignored, and @samp{\}
@end enumerate
If no command name results, the variable assignments affect the current
-shell environment. Otherwise, the variables are added to the environment
+shell environment.
+In the case of such a command (one that consists only of assignment
+statements and redirections), assignment statements are performed before
+redirections.
+Otherwise, the variables are added to the environment
of the executed command and do not affect the current shell environment.
If any of the assignments attempts to assign a value to a readonly variable,
an error occurs, and the command exits with a non-zero status.
@cindex command search
After a command has been split into words, if it results in a
-simple command and an optional list of arguments, the following
-actions are taken.
+simple command and an optional list of arguments, the shell performs
+the following actions.
@enumerate
@item
A command invoked in this separate environment cannot affect the
shell's execution environment.
+A @dfn{subshell} is a copy of the shell process.
+
Command substitution, commands grouped with parentheses,
and asynchronous commands are invoked in a
subshell environment that is a duplicate of the shell environment,
All builtins return an exit status of 2 to indicate incorrect usage,
generally invalid options or missing arguments.
+The exit status of the last command is available in the special
+parameter $? (@pxref{Special Parameters}).
+
@node Signals
@subsection Signals
@cindex signal handling
immediately with an exit status greater than 128, immediately after
which the trap is executed.
+When job control is not enabled, and Bash is waiting for a foreground
+command to complete, the shell receives keyboard-generated signals
+such as @code{SIGINT} (usually generated by @samp{^C}) that users
+commonly intend to send to that command.
+This happens because the shell and the command are in the same process
+group as the terminal, and @samp{^C} sends @code{SIGINT} to all processes
+in that process group.
+See @ref{Job Control}, for a more in-depth discussion of process groups.
+
+When Bash is running without job control enabled and receives @code{SIGINT}
+while waiting for a foreground command, it waits until that foreground
+command terminates and then decides what to do about the @code{SIGINT}:
+
+@enumerate
+@item
+If the command terminates due to the @code{SIGINT}, Bash concludes
+that the user meant to end the entire script, and acts on the
+@code{SIGINT} (e.g., by running a @code{SIGINT} trap or exiting itself);
+
+@item
+If the pipeline does not terminate due to @code{SIGINT}, the program
+handled the @code{SIGINT} itself and did not treat it as a fatal signal.
+In that case, Bash does not treat @code{SIGINT} as a fatal signal,
+either, instead assuming that the @code{SIGINT} was used as part of the
+program's normal operation (e.g., @command{emacs} uses it to abort editing
+commands) or deliberately discarded. However, Bash will run any
+trap set on @code{SIGINT}, as it does with any other trapped signal it
+receives while it is waiting for the foreground command to
+complete, for compatibility.
+@end enumerate
+
@node Shell Scripts
@section Shell Scripts
@cindex shell script
A shell script may be made executable by using the @code{chmod} command
to turn on the execute bit. When Bash finds such a file while
-searching the @env{$PATH} for a command, it spawns a subshell to
-execute it. In other words, executing
+searching the @env{$PATH} for a command, it creates a
+new instance of itself
+to execute it.
+In other words, executing
@example
filename @var{arguments}
@end example
Read and execute commands from the @var{filename} argument in the
current shell context. If @var{filename} does not contain a slash,
-the @env{PATH} variable is used to find @var{filename}.
-When Bash is not in @sc{posix} mode, the current directory is searched
+the @env{PATH} variable is used to find @var{filename},
+but @var{filename} does not need to be executable.
+When Bash is not in @sc{posix} mode, it searches the current directory
if @var{filename} is not found in @env{$PATH}.
If any @var{arguments} are supplied, they become the positional
parameters when @var{filename} is executed. Otherwise the positional
parameters are unchanged.
-If the @option{-T} option is enabled, @code{source} inherits any trap on
+If the @option{-T} option is enabled, @code{.} inherits any trap on
@code{DEBUG}; if it is not, any @code{DEBUG} trap string is saved and
-restored around the call to @code{source}, and @code{source} unsets the
+restored around the call to @code{.}, and @code{.} unsets the
@code{DEBUG} trap while it executes.
If @option{-T} is not set, and the sourced file changes
-the @code{DEBUG} trap, the new value is retained when @code{source} completes.
+the @code{DEBUG} trap, the new value is retained when @code{.} completes.
The return status is the exit status of the last command executed, or
zero if no commands are executed. If @var{filename} is not found, or
cannot be read, the return status is non-zero.
@item cd
@btindex cd
@example
-cd [-L|[-P [-e]] [-@@] [@var{directory}]
+cd [-L|[-P [-e]]] [-@@] [@var{directory}]
@end example
Change the current working directory to @var{directory}.
If @var{directory} is not supplied, the value of the @env{HOME}
shell variable is used.
-Any additional arguments following @var{directory} are ignored.
If the shell variable
@env{CDPATH} exists, it is used as a search path:
each directory name in @env{CDPATH} is searched for
the names is not a valid shell variable name, or @option{-f} is supplied
with a name that is not a shell function.
+@item false
+@btindex false
+@example
+false
+@end example
+
+Does nothing, returns a non-zero status.
+
@item getopts
@btindex getopts
@example
hash [-r] [-p @var{filename}] [-dt] [@var{name}]
@end example
-Each time @code{hash} is invoked, it remembers the full pathnames of the
+Each time @code{hash} is invoked, it remembers the full filenames of the
commands specified as @var{name} arguments,
so they need not be searched for on subsequent invocations.
The commands are found by searching through the directories listed in
@env{$PATH}.
-Any previously-remembered pathname is discarded.
+Any previously-remembered filename is discarded.
The @option{-p} option inhibits the path search, and @var{filename} is
used as the location of @var{name}.
The @option{-r} option causes the shell to forget all remembered locations.
+Assigning to the @env{PATH} variable also clears all hashed filenames.
The @option{-d} option causes the shell to forget the remembered location
of each @var{name}.
If the @option{-t} option is supplied, the full pathname to which each
@end enumerate
@item 4 arguments
+The following conditions are applied in the order listed.
+
+@enumerate
+@item
If the first argument is @samp{!}, the result is the negation of
the three-argument expression composed of the remaining arguments.
+@item
+If the first argument is exactly @samp{(} and the fourth argument is
+exactly @samp{)}, the result is the two-argument test of the second
+and third arguments.
+@item
Otherwise, the expression is parsed and evaluated according to
precedence using the rules listed above.
+@end enumerate
@item 5 or more arguments
The expression is parsed and evaluated according to precedence
using the rules listed above.
@end table
-When used with @code{test} or @samp{[}, the @samp{<} and @samp{>}
+If the shell is not in @sc{posix} mode,
+when used with @code{test} or @samp{[}, the @samp{<} and @samp{>}
operators sort lexicographically using ASCII ordering.
+If the shell is in @sc{posix} mode, these operators use the current locale.
+
+The historical operator-precedence parsing with 4 or more arguments can
+lead to ambiguities when it encounters strings that look like primaries.
+The @sc{posix} standard has deprecated the @option{-a} and @option{-o}
+primaries and enclosing expressions within parentheses.
+Scripts should no longer use them.
+It's much more reliable to restrict test invocations to a single primary,
+and to replace uses of @option{-a} and @option{-o} with the shell's
+@code{&&} and @code{||} list operators. For example, use
+
+@example
+test -n string1 && test -n string2
+@end example
+
+@noindent
+instead of
+
+@example
+test -n string1 -a -n string2
+@end example
@item times
@btindex times
@item trap
@btindex trap
@example
-trap [-lp] [@var{arg}] [@var{sigspec} @dots{}]
+trap [-Plp] [@var{action}] [@var{sigspec} @dots{}]
@end example
-The commands in @var{arg} are to be read and executed when the
-shell receives signal @var{sigspec}. If @var{arg} is absent (and
+The @var{action} is a command that is read and executed when the
+shell receives signal @var{sigspec}. If @var{action} is absent (and
there is a single @var{sigspec}) or
equal to @samp{-}, each specified signal's disposition is reset
to the value it had when the shell was started.
-If @var{arg} is the null string, then the signal specified by
+If @var{action} is the null string, then the signal specified by
each @var{sigspec} is ignored by the shell and commands it invokes.
-If @var{arg} is not present and @option{-p} has been supplied,
-the shell displays the trap commands associated with each @var{sigspec}.
-If no arguments are supplied, or
-only @option{-p} is given, @code{trap} prints the list of commands
-associated with each signal number in a form that may be reused as
-shell input.
-The @option{-l} option causes the shell to print a list of signal names
+
+If no arguments are supplied, @code{trap} prints the actions
+associated with each trapped signal
+as a set of @code{trap} commands that can be reused as shell input to
+restore the current signal dispositions.
+If @var{action} is not present and @option{-p} has been supplied,
+@code{trap} displays the trap commands associated with each @var{sigspec},
+or, if no @var{sigspec}s are supplied, for all trapped signals,
+as a set of @code{trap} commands that can be reused as shell input to
+restore the current signal dispositions.
+The @option{-P} option behaves similarly, but displays only the actions
+associated with each @var{sigspec} argument.
+@option{-P} requires at least one @var{sigspec} argument.
+The @option{-P} or @option{-p} options to @code{trap} may be
+used in a subshell environment (e.g., command substitution) and,
+as long as they are used before @code{trap} is used to change a
+signal's handling, will display the state of its parent's traps.
+
+The @option{-l} option causes @code{trap} to print a list of signal names
and their corresponding numbers.
Each @var{sigspec} is either a signal name or a signal number.
Signal names are case insensitive and the @code{SIG} prefix is optional.
If a @var{sigspec}
-is @code{0} or @code{EXIT}, @var{arg} is executed when the shell exits.
-If a @var{sigspec} is @code{DEBUG}, the command @var{arg} is executed
+is @code{0} or @code{EXIT}, @var{action} is executed when the shell exits.
+If a @var{sigspec} is @code{DEBUG}, @var{action} is executed
before every simple command, @code{for} command, @code{case} command,
-@code{select} command, every arithmetic @code{for} command, and before
-the first command executes in a shell function.
+@code{select} command, (( arithmetic command, [[ conditional command,
+arithmetic @code{for} command,
+and before the first command executes in a shell function.
Refer to the description of the @code{extdebug} option to the
@code{shopt} builtin (@pxref{The Shopt Builtin}) for details of its
effect on the @code{DEBUG} trap.
-If a @var{sigspec} is @code{RETURN}, the command @var{arg} is executed
+If a @var{sigspec} is @code{RETURN}, @var{action} is executed
each time a shell function or a script executed with the @code{.} or
@code{source} builtins finishes executing.
-If a @var{sigspec} is @code{ERR}, the command @var{arg}
+If a @var{sigspec} is @code{ERR}, @var{action}
is executed whenever
a pipeline (which may consist of a single simple
command), a list, or a compound command returns a
These are the same conditions obeyed by the @code{errexit} (@option{-e})
option.
-Signals ignored upon entry to the shell cannot be trapped or reset.
+Signals ignored upon entry to a non-interactive shell cannot be trapped or
+reset.
+Interactive shells permit trapping signals ignored on entry.
Trapped signals that are not being ignored are reset to their original
values in a subshell or subshell environment when one is created.
The return status is zero unless a @var{sigspec} does not specify a
valid signal.
+@item true
+@btindex true
+@example
+true
+@end example
+
+Does nothing, returns a 0 status.
+
@item umask
@btindex umask
@example
buffer and the @code{READLINE_POINT} and @code{READLINE_MARK} variables
to the current location of the insertion point and the saved insertion
point (the @var{mark}), respectively.
+The shell assigns any numeric argument the user supplied to the
+@code{READLINE_ARGUMENT} variable.
+If there was no argument, that variable is not set.
If the executed command changes the value of any of @code{READLINE_LINE},
@code{READLINE_POINT}, or @code{READLINE_MARK}, those new values will be
reflected in the editing state.
The @option{-f} option means to load the new builtin command @var{name}
from shared object @var{filename}, on systems that support dynamic loading.
+Bash will use the value of the @env{BASH_LOADABLES_PATH} variable as a
+colon-separated list of directories in which to search for @var{filename}.
+The default is system-dependent.
The @option{-d} option will delete a builtin loaded with @option{-f}.
If there are no options, a list of the shell builtins is displayed.
builtins. If @option{-s} is used with @option{-f}, the new builtin becomes
a special builtin (@pxref{Special Builtins}).
+If no options are supplied and a @var{name} is not a shell builtin,
+@code{enable} will attempt to load @var{name} from a shared object named
+@var{name}, as if the command were
+@samp{enable -f @var{name} @var{name}}.
+
The return status is zero unless a @var{name} is not a shell builtin
or there is an error loading a new builtin from a shared object.
children.
If @var{name} is @samp{-}, the set of shell options is made local to the
function in which @code{local} is invoked: shell options changed using
-the @code{set} builtin inside the function are restored to their original
+the @code{set} builtin inside the function
+after the call to @code{local}
+are restored to their original
values when the function returns.
The restore is effected as if a series of @code{set} commands were executed
to restore the values that were in place before the function.
escape sequences, which are converted and copied to the standard output, and
format specifications, each of which causes printing of the next successive
@var{argument}.
-In addition to the standard @code{printf(1)} formats, @code{printf}
-interprets the following extensions:
+In addition to the standard @code{printf(3)} format characters
+@code{csndiouxXeEfFgGaA},
+@code{printf} interprets the following additional format specifiers:
@table @code
@item %b
@item %q
Causes @code{printf} to output the
corresponding @var{argument} in a format that can be reused as shell input.
+@code{%q} and @code{%Q}P use the ANSI-C quoting style (@pxref{ANSI-C Quoting})
+if any characters
+in the argument string require it, and backslash quoting otherwise.
+If the format string uses the @code{printf} @var{alternate form}, these two
+formats quote the argument string using single quotes.
+
+@item %Q
+like @code{%q}, but applies any supplied precision to the @var{argument}
+before quoting it.
@item %(@var{datefmt})T
Causes @code{printf} to output the date-time string resulting from using
@var{datefmt} as a format string for @code{strftime}(3).
@end table
@noindent
-The %b, %q, and %T directives all use the field width and precision
+The %b, %q, and %T format specifiers all use the field width and precision
arguments from the format specification and write that many bytes from
(or use that wide a field for) the expanded argument, which usually
contains more characters than the original.
+The %n format specifier accepts a corresponding argument that is treated
+as a shell variable name.
+
+The %s and %c format specifiers accept an l (long) modifier, which forces
+them to convert the argument string to a wide-character string and apply
+any supplied field width and precision in terms of characters, not bytes.
+
Arguments to non-string format specifiers are treated as C language constants,
except that a leading plus or minus sign is allowed, and if the leading
character is a single or double quote, the value is the ASCII value of
The @var{format} is reused as necessary to consume all of the @var{arguments}.
If the @var{format} requires more @var{arguments} than are supplied, the
extra format specifications behave as if a zero value or null string, as
-appropriate, had been supplied. The return value is zero on success,
-non-zero on failure.
+appropriate, had been supplied.
+The return value is zero on success,
+non-zero if an invalid option is supplied or a write or assignment error
+occurs.
@item read
@btindex read
If @code{read} times out, @code{read} saves any partial input read into
the specified variable @var{name}.
If @var{timeout} is 0, @code{read} returns immediately, without trying to
-read any data. The exit status is 0 if input is available on
-the specified file descriptor, non-zero otherwise.
+read any data.
+The exit status is 0 if input is available on the specified file descriptor,
+or the read will return EOF,
+non-zero otherwise.
The exit status is greater than 128 if the timeout is exceeded.
@item -u @var{fd}
command name.
If the @option{-t} option is used, @code{type} prints a single word
-which is one of @samp{alias}, @samp{function}, @samp{builtin},
-@samp{file} or @samp{keyword},
-if @var{name} is an alias, shell function, shell builtin,
-disk file, or shell reserved word, respectively.
+which is one of @samp{alias}, @samp{keyword}, @samp{function},
+@samp{builtin}, or @samp{file},
+if @var{name} is an alias, shell reserved word, shell function,
+shell builtin, or executable disk file, respectively.
If the @var{name} is not found, then nothing is printed, and
@code{type} returns a failure status.
If the @option{-p} option is used, @code{type} either returns the name
-of the disk file that would be executed, or nothing if @option{-t}
-would not return @samp{file}.
+of the executable file that would be found by searching @code{$PATH},
+or nothing if @option{-t} would not return @samp{file}.
The @option{-P} option forces a path search for each @var{name}, even if
@option{-t} would not return @samp{file}.
-If a command is hashed, @option{-p} and @option{-P} print the hashed value,
-which is not necessarily the file that appears first in @code{$PATH}.
+If a @var{name} is present in the table of hashed commands,
+options @option{-p} and @option{-P} print the hashed value, which is not
+necessarily the file that appears first in @code{$PATH}.
If the @option{-a} option is used, @code{type} returns all of the places
-that contain an executable named @var{file}.
-This includes aliases and functions, if and only if the @option{-p} option
-is not also used.
+that contain a command named @var{name}.
+This includes aliases, reserved words, functions, and builtins,
+but the path search options (@option{-p} and @option{-P}) can be supplied
+to restrict the output to executable files.
+If @option{-a} is supplied with @option{-p}, @code{type} does not look
+in the table of hashed commands, and only performs a @code{PATH}
+search for @var{name}.
If the @option{-f} option is used, @code{type} does not attempt to find
shell functions, as with the @code{command} builtin.
@item set
@btindex set
@example
-set [--abefhkmnptuvxBCEHPT] [-o @var{option-name}] [@var{argument} @dots{}]
-set [+abefhkmnptuvxBCEHPT] [+o @var{option-name}] [@var{argument} @dots{}]
+set [-abefhkmnptuvxBCEHPT] [-o @var{option-name}] [--] [-] [@var{argument} @dots{}]
+set [+abefhkmnptuvxBCEHPT] [+o @var{option-name}] [--] [-] [@var{argument} @dots{}]
+set -o
+set +o
@end example
If no options or arguments are supplied, @code{set} displays the names
@item -o @var{option-name}
-Set the option corresponding to @var{option-name}:
+Set the option corresponding to @var{option-name}.
+If @option{-o} is supplied with no @var{option-name},
+@code{set} prints the current shell options settings.
+If @option{+o} is supplied with no @var{option-name},
+@code{set} prints a series of
+@code{set}
+commands to recreate the current option settings
+on the standard output.
+Valid option names are:
@table @code
@item allexport
Turning this option off causes the effective user
and group ids to be set to the real user and group ids.
+@item -r
+Enable restricted shell mode.
+This option cannot be unset once it has been set.
+
@item -t
Exit after reading and executing one command.
@item -u
Treat unset variables and parameters other than the special parameters
-@samp{@@} or @samp{*} as an error when performing parameter expansion.
+@samp{@@} or @samp{*},
+or array variables subscripted with @samp{@@} or @samp{*},
+as an error when performing parameter expansion.
An error message will be written to the standard error, and a non-interactive
shell will exit.
@item -x
Print a trace of simple commands, @code{for} commands, @code{case}
commands, @code{select} commands, and arithmetic @code{for} commands
-and their arguments or associated word lists after they are
-expanded and before they are executed. The value of the @env{PS4}
-variable is expanded and the resultant value is printed before
+and their arguments or associated word lists to standard error
+after they are expanded and before they are executed.
+The shell prints the expanded value of the @env{PS4} variable before
the command and its expanded arguments.
@item -B
The list of @code{shopt} options is:
@table @code
-@item assoc_expand_once
-If set, the shell suppresses multiple evaluation of associative array
-subscripts during arithmetic expression evaluation, while executing
+@item array_expand_once
+If set, the shell suppresses multiple evaluation of
+associative and indexed array subscripts
+during arithmetic expression evaluation, while executing
builtins that can perform variable assignments,
and while executing builtins that perform array dereferencing.
+@item assoc_expand_once
+Deprecated; a synonym for @code{array_expand_once}.
+
@item autocd
If set, a command name that is the name of a directory is executed as if
it were the argument to the @code{cd} command.
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
+This is active only when Bash is using backslashes to quote completed
filenames.
This variable is set by default, which is the default Bash behavior in
versions through 4.2.
@item 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
+filename completion. This changes the contents of the Readline editing
buffer.
If not set, Bash attempts to preserve what the user typed.
@samp{b} will not collate between @samp{A} and @samp{B},
and upper-case and lower-case ASCII characters will collate together.
+@item globskipdots
+If set, filename expansion will never match the filenames
+@samp{.} and @samp{..},
+even if the pattern begins with a @samp{.}.
+This option is enabled by default.
+
@item globstar
If set, the pattern @samp{**} used in a filename expansion context will
match all files and zero or more directories and subdirectories.
@item nocasematch
If set, Bash matches patterns in a case-insensitive fashion when
performing matching while executing @code{case} or @code{[[}
-conditional commands,
+conditional commands (@pxref{Conditional Constructs},
when performing pattern substitution word expansions,
or when filtering possible completions as part of programmable completion.
+@item 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.
+
@item nullglob
If set, Bash allows filename patterns which match no
files to expand to a null string, rather than themselves.
+@item patsub_replacement
+If set, Bash
+expands occurrences of @samp{&} in the replacement string of pattern
+substitution to the text matched by the pattern, as described
+above (@pxref{Shell Parameter Expansion}).
+This option is enabled by default.
+
@item progcomp
If set, the programmable completion facilities
(@pxref{Programmable Completion}) are enabled.
number of positional parameters.
@item sourcepath
-If set, the @code{source} builtin uses the value of @env{PATH}
+If set, the @code{.} (@code{source}) builtin uses the value of @env{PATH}
to find the directory containing the file supplied as an argument.
This option is enabled by default.
+@item varredir_close
+If set, the shell automatically closes file descriptors assigned using the
+@code{@{varname@}} redirection syntax (@pxref{Redirections}) instead of
+leaving them open when the command completes.
+
@item xpg_echo
If set, the @code{echo} builtin expands backslash-escape sequences
by default.
@item BASH_ARGC
An array variable whose values are the number of parameters in each
-frame of the current bash execution call stack. The number of
+frame of the current Bash execution call stack. The number of
parameters to the current subroutine (shell function or script executed
with @code{.} or @code{source}) is at the top of the stack. When a
subroutine is executed, the number of parameters passed is pushed onto
Setting @code{extdebug} after the shell has started to execute a script,
or referencing this variable when @code{extdebug} is not set,
may result in inconsistent values.
+Assignments to @env{BASH_ARGC} have no effect, and it may not be unset.
@item BASH_ARGV
-An array variable containing all of the parameters in the current bash
+An array variable containing all of the parameters in the current Bash
execution call stack. The final parameter of the last subroutine call
is at the top of the stack; the first parameter of the initial call is
at the bottom. When a subroutine is executed, the parameters supplied
Setting @code{extdebug} after the shell has started to execute a script,
or referencing this variable when @code{extdebug} is not set,
may result in inconsistent values.
+Assignments to @env{BASH_ARGV} have no effect, and it may not be unset.
@item BASH_ARGV0
When referenced, this variable expands to the name of the shell or shell
@code{$@{FUNCNAME[$i]@}} was called (or @code{$@{BASH_LINENO[$i-1]@}} if
referenced within another shell function).
Use @code{LINENO} to obtain the current line number.
+Assignments to @env{BASH_LINENO} have no effect, and it may not be unset.
@item BASH_LOADABLES_PATH
A colon-separated list of directories in which the shell looks for
dynamically loadable builtins specified by the
@code{enable} command.
+@item BASH_MONOSECONDS
+Each time this variable is referenced, it expands to the value returned
+by the system's monotonic clock, if one is available.
+If there is no monotonic clock, this is equivalent to @env{EPOCHSECONDS}.
+If @env{BASH_MONOSECONDS}
+is unset, it loses its special properties, even if it is
+subsequently reset.
+
@item BASH_REMATCH
An array variable whose members are assigned by the @samp{=~} binary
operator to the @code{[[} conditional command
variable are defined.
The shell function @code{$@{FUNCNAME[$i]@}} is defined in the file
@code{$@{BASH_SOURCE[$i]@}} and called from @code{$@{BASH_SOURCE[$i+1]@}}
+Assignments to @env{BASH_SOURCE} have no effect, and it may not be unset.
@item BASH_SUBSHELL
Incremented by one within each subshell or subshell environment when
is unset, it loses its special properties, even if it is
subsequently reset.
+@item BASH_TRAPSIG
+Set to the signal number corresponding to the trap action being executed
+during its execution.
+See the description of @code{trap}
+(@pxref{Bourne Shell Builtins})
+for information about signal numbers and trap execution.
+
@item BASH_VERSINFO
A readonly array variable (@pxref{Arrays})
whose members hold version information for this instance of Bash.
Emacs shell buffer and disables line editing.
@item ENV
-Expanded and executed similarlty to @code{BASH_ENV}
+Expanded and executed similarly to @code{BASH_ENV}
(@pxref{Bash Startup Files})
when an interactive shell is invoked in
@sc{posix} Mode (@pxref{Bash POSIX Mode}).
The pattern matching honors the setting of the @code{extglob} shell
option.
+@item GLOBSORT
+Control how the results of filename expansion are sorted.
+The value of this variable specifies the sort criteria and sort order for
+the results of filename expansion.
+If this variable is unset or set to the null string, filename expansion
+uses the historial behavior of sorting by name.
+If set, a valid value begins with an optional @samp{+}, which is ignored,
+or @samp{-}, which reverses the sort order from ascending to descending,
+followed by a sort specifier.
+The valid sort specifiers are
+@samp{name},
+@samp{size},
+@samp{mtime},
+@samp{atime},
+@samp{ctime},
+and
+@samp{blocks},
+which sort the files on name, file size, modification time, access time,
+inode change time, and number of blocks, respectively.
+
+For example, a value of @code{-mtime} sorts the results in descending
+order by modification time (newest first).
+
+A sort specifier of @samp{nosort} disables sorting completely; the results
+are returned in the order they are read from the file system,.
+
+If the sort specifier is missing, it defaults to @var{name},
+so a value of @samp{+} is equivalent to the null string,
+and a value of @samp{-} sorts by name in descending order.
+
+Any invalid value restores the historical sorting behavior.
+
@item GROUPS
An array variable containing the list of groups of which the current
user is a member.
is unset, it loses its special properties, even if it is
subsequently reset.
+@item READLINE_ARGUMENT
+Any numeric argument given to a Readline command that was defined using
+@samp{bind -x} (@pxref{Bash Builtins}
+when it was invoked.
+
@item READLINE_LINE
The contents of the Readline line buffer, for use
with @samp{bind -x} (@pxref{Bash Builtins}).
The default variable for the @code{read} builtin.
@item SECONDS
-This variable expands to the number of seconds since the
-shell was started. Assignment to this variable resets
-the count to the value assigned, and the expanded value
-becomes the value assigned plus the number of seconds
+This variable expands to the number of seconds since the shell was started.
+Assignment to this variable resets the count to the value assigned, and the
+expanded value becomes the value assigned plus the number of seconds
since the assignment.
-The number of seconds at shell invocation and the current time is always
+The number of seconds at shell invocation and the current time are always
determined by querying the system clock.
If @env{SECONDS}
is unset, it loses its special properties,
The optional @var{p} is a digit specifying the precision, the number of
fractional digits after a decimal point.
A value of 0 causes no decimal point or fraction to be output.
-At most three places after the decimal point may be specified; values
-of @var{p} greater than 3 are changed to 3.
+At most six places after the decimal point may be specified;
+values of @var{p} greater than 6 are changed to 6.
If @var{p} is not specified, the value 3 is used.
The optional @code{l} specifies a longer format, including minutes, of
@subsubheading Invoked by remote shell daemon
Bash attempts to determine when it is being run with its standard input
-connected to a network connection, as when executed by the remote shell
-daemon, usually @code{rshd}, or the secure shell daemon @code{sshd}.
-If Bash determines it is being run in
-this fashion, it reads and executes commands from @file{~/.bashrc}, if that
+connected to a network connection, as when executed by
+the historical remote shell daemon, usually @code{rshd},
+or the secure shell daemon @code{sshd}.
+If Bash
+determines it is being run non-interactively in this fashion,
+it reads and executes commands from @file{~/.bashrc}, if that
file exists and is readable.
It will not do this if invoked as @code{sh}.
The @option{--norc} option may be used to inhibit this behavior, and the
@menu
* What is an Interactive Shell?:: What determines whether a shell is Interactive.
* Is this Shell Interactive?:: How to tell if a shell is interactive.
-* Interactive Shell Behavior:: What changes in a interactive shell?
+* Interactive Shell Behavior:: What changes in an interactive shell?
@end menu
@node What is an Interactive Shell?
@subsection What is an Interactive Shell?
An interactive shell
-is one started without non-option arguments, unless @option{-s} is
-specified, without specifying the @option{-c} option, and
+is one started without non-option arguments
+(unless @option{-s} is specified)
+and without specifying the @option{-c} option,
whose input and error output are both
connected to terminals (as determined by @code{isatty(3)}),
or one started with the @option{-i} option.
Parser syntax errors will not cause the shell to exit.
@item
-Simple spelling correction for directory arguments to the @code{cd}
-builtin is enabled by default (see the description of the @code{cdspell}
+If the @code{cdspell} shell option is enabled, the shell will attempt
+simple spelling correction for directory arguments to the @code{cd}
+builtin (see the description of the @code{cdspell}
option to the @code{shopt} builtin in @ref{The Shopt Builtin}).
+The @code{cdspell} option is only effective in interactive shells.
@item
The shell will check the value of the @env{TMOUT} variable and exit
@cindex expressions, conditional
Conditional expressions are used by the @code{[[} compound command
-and the @code{test} and @code{[} builtin commands. The @code{test}
+(@pxref{Conditional Constructs})
+and the @code{test} and @code{[} builtin commands
+(@pxref{Bourne Shell Builtins}).
+The @code{test}
and @code{[} commands determine their behavior based on the number
of arguments; see the descriptions of those commands for any other
command-specific actions.
The levels are listed in order of decreasing precedence.
@table @code
+@cindex arithmetic operators
+@cindex unary arithmetic operators
+@cindex binary arithmetic operators
+@cindex conditional arithmetic operator
+@cindex bitwise arithmetic operators
@item @var{id}++ @var{id}--
variable post-increment and post-decrement
@item ||
logical OR
-@item expr ? expr : expr
+@item expr ? if-true-expr : if-false-expr
conditional operator
@item = *= /= %= += -= <<= >>= &= ^= |=
@section Aliases
@cindex alias expansion
-@dfn{Aliases} allow a string to be substituted for a word when it is used
-as the first word of a simple command.
-The shell maintains a list of aliases that may be set and unset with
-the @code{alias} and @code{unalias} builtin commands.
+@dfn{Aliases} allow a string to be substituted for a word that is in
+a position in the input where it can be the first word of a simple
+command. Aliases have names and corresponding values that are set
+and unset using the @code{alias} and @code{unalias} builtin commands
+(@pxref{Shell Builtin Commands}).
+
+If the shell reads an unquoted word in the right position, it checks
+the word to see if it matches an alias name. If it matches, the shell
+replaces the word with the alias value, and reads that value as if it
+had been read instead of the word.
+The shell doesn't look at any characters following the word before
+attempting alias substitution.
-The first word of each simple command, if unquoted, is checked to see
-if it has an alias.
-If so, that word is replaced by the text of the alias.
The characters @samp{/}, @samp{$}, @samp{`}, @samp{=} and any of the
shell metacharacters or quoting characters listed above may not appear
in an alias name.
This means that one may alias @code{ls} to @code{"ls -F"},
for instance, and Bash does not try to recursively expand the
replacement text.
+
If the last character of the alias value is a
@code{blank}, then the next command word following the
alias is also checked for alias expansion.
There is no mechanism for using arguments in the replacement text,
as in @code{csh}.
If arguments are needed, use a shell function
-(@pxref{Shell Functions}).
+(@pxref{Shell Functions}) instead.
Aliases are not expanded when the shell is not interactive,
unless the @code{expand_aliases} shell option is set using
otherwise the index of the element assigned is the last index assigned
to by the statement plus one. Indexing starts at zero.
-Each @var{value} in the list undergoes all the shell expansions
-described above (@pxref{Shell Expansions}).
+Each @var{value} in the list undergoes the shell expansions
+described above (@pxref{Shell Expansions}),
+but @var{value}s that are valid variable assignments
+including the brackets and subscript do not undergo
+brace expansion and word splitting, as with individual
+variable assignments.
When assigning to an associative array, the words in a compound assignment
may be either assignment statements, for which the subscript is required,
@var{name}, so negative indices count back from the end of the
array, and an index of -1 references the last element.
+The @samp{+=} operator will append to an array variable when assigning
+using the compound assignment syntax; see @ref{Shell Parameters} above.
+
Any element of an array may be referenced using
@code{$@{@var{name}[@var{subscript}]@}}.
The braces are required to avoid
Negative subscripts to indexed arrays are interpreted as described above.
Unsetting the last element of an array variable does not unset the variable.
@code{unset @var{name}}, where @var{name} is an array, removes the
-entire array. A subscript of @samp{*} or @samp{@@} also removes the
entire array.
+@code{unset @var{name}[@var{subscript}]} behaves differently
+depending on the array type when given a
+subscript of @samp{*} or @samp{@@}.
+When @var{name} is an associative array, it removes the element with key
+@samp{*} or @samp{@@}.
+If @var{name} is an indexed array, @code{unset} removes all of the elements,
+but does not remove the array itself.
When using a variable name with a subscript as an argument to a command,
such as with @code{unset}, without using the word expansion syntax
an invalid option is encountered, the directory stack
is empty, or a non-existent directory stack entry is specified.
-If the @code{popd} command is successful, a @code{dirs}
-is performed as well, and the return status is 0.
+If the @code{popd} command is successful,
+Bash runs @code{dirs} to show the final contents of the directory stack,
+and the return status is 0.
@btindex pushd
@item pushd
the directory stack is empty or a non-existent directory stack element
is specified.
-If the @code{pushd} command is successful, a @code{dirs} is performed as well.
+If the @code{pushd} command is successful,
+Bash runs @code{dirs} to show the final contents of the directory stack.
@end table
@item
Specifying the @option{-p} option to the @code{command} builtin.
@item
-Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}.
+Turning off restricted mode with @samp{set +r} or @samp{shopt -u restricted_shell}.
@end itemize
These restrictions are enforced after any startup files are read.
The restricted shell mode is only one component of a useful restricted
environment. It should be accompanied by setting @env{PATH} to a value
that allows execution of only a few verified commands (commands that
-allow shell escapes are particularly vulnerable), leaving the user
-in a non-writable directory other than his home directory after login,
+allow shell escapes are particularly vulnerable), changing the current
+directory to a non-writable directory other than @env{$HOME} after login,
not allowing the restricted shell to execute shell scripts, and cleaning
the environment of variables that cause some commands to modify their
behavior (e.g., @env{VISUAL} or @env{PAGER}).
@node Bash POSIX Mode
-@section Bash POSIX Mode
+@section Bash and POSIX
+
+@subsection What is POSIX?
+@cindex POSIX description
+
+@sc{posix} is the name for a family of standards based on Unix.
+A number of Unix services, tools, and functions are part of the standard,
+ranging from the basic system calls and C library functions to common
+applications and tools to system administration and management.
+
+The @sc{posix} Shell and Utilities standard was originally developed by
+IEEE Working Group 1003.2 (POSIX.2).
+The first edition of the 1003.2 standard was published in 1992.
+It was merged with the original IEEE 1003.1 Working Group and is
+currently maintained by the Austin Group (a joint working group of the
+IEEE, The Open Group and ISO/IEC SC22/WG15).
+Today the Shell and Utilities are a volume within the set of documents that
+make up IEEE Std 1003.1-2017, and thus the former POSIX.2 (from 1992)
+is now part of the current unified @sc{posix} standard.
+
+The Shell and Utilities volume concentrates on the command
+interpreter interface and utility programs commonly executed from
+the command line or by other programs.
+The standard is freely available on the web at
+@url{https://pubs.opengroup.org/onlinepubs/9699919799/utilities/contents.html}.
+
+Bash is concerned with the aspects of the shell's behavior defined
+by the @sc{posix} Shell and Utilities volume. The shell command
+language has of course been standardized, including the basic flow
+control and program execution constructs, I/O redirection and
+pipelines, argument handling, variable expansion, and quoting.
+
+The @i{special} builtins, which must be implemented as part of the
+shell to provide the desired functionality, are specified as
+being part of the shell; examples of these are @code{eval} and
+@code{export}.
+Other utilities appear in the sections of POSIX not
+devoted to the shell which are commonly (and in some cases must
+be) implemented as builtin commands, such as
+@code{read} and @code{test}.
+POSIX also specifies aspects of the shell's interactive
+behavior, including job control and command
+line editing.
+Only vi-style line editing commands have been
+standardized; emacs editing commands were left out due to
+objections.
+
+@subsection Bash POSIX Mode
@cindex POSIX Mode
+Although Bash is an implementation of the @sc{posix} shell
+specification, there are areas where the Bash default behavior
+differs from the specification.
+The Bash @dfn{posix mode} changes the Bash
+behavior in these areas so that it conforms to the standard more closely.
+
Starting Bash with the @option{--posix} command-line option or executing
@samp{set -o posix} while Bash is running will cause Bash to conform more
closely to the @sc{posix} standard by changing the behavior to
Reserved words appearing in a context where reserved words are recognized
do not undergo alias expansion.
+@item
+Alias expansion is performed when initially parsing a command substitution.
+The default mode generally defers it, when enabled, until the command
+substitution is executed. This means that command substitution will not
+expand aliases that are defined after the command substitution is initially
+parsed (e.g., as part of a function definition).
+
@item
The @sc{posix} @env{PS1} and @env{PS2} expansions of @samp{!} to
the history number and @samp{!!} to @samp{!} are enabled,
Function names may not be the same as one of the @sc{posix} special
builtins.
+@item
+Even if a shell function whose name contains a slash was defined before
+entering @sc{posix} mode, the shell will not execute a function whose name
+contains one or more slashes.
+
@item
@sc{posix} special builtins are found before shell functions
during command lookup.
redirection errors, variable assignment errors for assignments preceding
the command name, and so on.
+@item
+The @code{unset} builtin with the @option{-v} option specified returns a
+fatal error if it attempts to unset a @code{readonly} or @code{non-unsettable}
+variable, or encounters a variable name argument that is an invalid identifier,
+which causes a non-interactive shell to exit.
+
@item
A non-interactive shell exits with an error status if a variable
assignment error occurs when no command name follows the assignment
@samp{#} and @samp{?} special parameters.
@item
-When expanding the @samp{*} special parameter in a pattern context where the
+Expanding the @samp{*} special parameter in a pattern context where the
expansion is double-quoted does not treat the @code{$*} as if it were
double-quoted.
first argument.
@item
-@code{trap -p} displays signals whose dispositions are set to SIG_DFL and
-those that were ignored when the shell started.
+@code{trap -p} without arguments displays signals whose dispositions are
+set to SIG_DFL and those that were ignored when the shell started, not
+just trapped signals.
@item
The @code{.} and @code{source} builtins do not search the current directory
@item
The default editor used by @code{fc} is @code{ed}.
+@item
+If there are too many arguments supplied to @code{fc -s}, @code{fc} prints
+an error message and returns failure.
+
@item
The @code{type} and @code{command} builtins will not report a non-executable
file as having been found, though the shell will attempt to execute such a
If Bash receives a trapped signal while executing @code{read}, the trap
handler executes and @code{read} returns an exit status greater than 128.
+@item
+The @code{printf} builtin uses @code{double} (via @code{strtod}) to convert
+arguments corresponding to floating point conversion specifiers, instead of
+@code{long double} if it's available. The @samp{L} length modifier forces
+@code{printf} to use @code{long double} if it's available.
+
@item
Bash removes an exited background process's status from the list of such
statuses after the @code{wait} builtin is used to obtain it.
+@item
+A double quote character (@samp{"}) is treated specially when it appears
+in a backquoted command substitution in the body of a here-document that
+undergoes expansion.
+That means, for example, that a backslash preceding a double quote
+character will escape it and the backslash will be removed.
+
+@item
+The @code{test} builtin compares strings using the current locale when
+processing the @samp{<} and @samp{>} binary operators.
+
+@item
+The @code{test} builtin's @option{-t} unary primary requires an argument.
+Historical versions of @code{test} made the argument optional in certain
+cases, and bash attempts to accommodate those for backwards compatibility.
+
+@item
+Command substitutions don't set the @samp{?} special parameter. The exit
+status of a simple command without a command word is still the exit status
+of the last command substitution that occurred while evaluating the variable
+assignments and redirections in that command, but that does not happen until
+after all of the assignments and redirections.
+
@end enumerate
There is other @sc{posix} behavior that Bash does not implement by
entries if @code{FCEDIT} is unset, rather than defaulting directly to
@code{ed}. @code{fc} uses @code{ed} if @code{EDITOR} is unset.
+@item
+A non-interactive shell does not exit if a variable assignment preceding
+the @code{command} builtin or another non-special builtin fails.
+
@item
As noted above, Bash requires the @code{xpg_echo} option to be enabled for
the @code{echo} builtin to be fully conformant.
@cindex Compatibility Level
@cindex Compatibility Mode
-Bash-4.0 introduced the concept of a `shell compatibility level', specified
-as a set of options to the shopt builtin
+Bash-4.0 introduced the concept of a @dfn{shell compatibility level},
+specified as a set of options to the shopt builtin
(@code{compat31},
@code{compat32},
@code{compat40},
This section does not mention behavior that is standard for a particular
version (e.g., setting @code{compat32} means that quoting the rhs of the regexp
matching operator quotes special regexp characters in the word, which is
-default behavior in bash-3.2 and above).
+default behavior in bash-3.2 and subsequent versions).
If a user enables, say, @code{compat32}, it may affect the behavior of other
compatibility levels up to and including the current compatibility level.
has no special effect
@end itemize
-@item compat32
-@itemize @bullet
-@item
-interrupting a command list such as "a ; b ; c" causes the execution
-of the next command in the list (in bash-4.0 and later versions,
-the shell acts as if it received the interrupt, so
-interrupting one command in a list aborts the execution of the
-entire list)
-@end itemize
-
@item compat40
@itemize @bullet
@item
@item
the shell does not print a warning message if an attempt is made to
use a quoted compound assignment as an argument to declare
-(declare -a foo='(1 2)'). Later versions warn that this usage is
+(e.g., declare -a foo='(1 2)'). Later versions warn that this usage is
deprecated
@item
word expansion errors are considered non-fatal errors that cause the
output that can be reused as input. Bash-5.1 suppresses that message
when the @option{-l} option is supplied.
@end itemize
+
+@item compat51 (set using BASH_COMPAT)
+@itemize @bullet
+@item
+The @code{unset} builtin will unset the array @code{a} given an argument like
+@samp{a[@@]}.
+Bash-5.2 will unset an element with key @samp{@@} (associative arrays)
+or remove all the elements without unsetting the array (indexed arrays)
+@item
+arithmetic commands ( ((...)) ) and the expressions in an arithmetic for
+statement can be expanded more than once
+@item
+expressions used as arguments to arithmetic operators in the @code{[[}
+conditional command can be expanded more than once
+@item
+the expressions in substring parameter brace expansion can be
+expanded more than once
+@item
+the expressions in the $(( ... )) word expansion can be expanded
+more than once
+@item
+arithmetic expressions used as indexed array subscripts can be
+expanded more than once
+@item
+@code{test -v}, when given an argument of @samp{A[@@]}, where @var{A} is
+an existing associative array, will return true if the array has any set
+elements.
+Bash-5.2 will look for and report on a key named @samp{@@}
+@item
+the $@{@var{parameter}[:]=@var{value}@} word expansion will return
+@var{value}, before any variable-specific transformations have been
+performed (e.g., converting to lowercase).
+Bash-5.2 will return the final value assigned to the variable.
+@item
+Parsing command substitutions will behave as if extended glob
+(@pxref{The Shopt Builtin})
+is enabled, so that parsing a command substitution containing an extglob
+pattern (say, as part of a shell function) will not fail.
+This assumes the intent is to enable extglob before the command is executed
+and word expansions are performed.
+It will fail at word expansion time if extglob hasn't been
+enabled by the time the command is executed.
+@end itemize
@end table
@node Job Control
This is useful only when the @option{-n} option is supplied.
Supplying the @option{-f} option, when job control is enabled,
forces @code{wait} to wait for each @var{pid} or @var{jobspec} to
-terminate before returning its status, intead of returning when it changes
+terminate before returning its status, instead of returning when it changes
status.
If neither @var{jobspec} nor @var{pid} specifies an active child process
of the shell, the return status is 127.
+If @code{wait} is interrupted by a signal, the return status will be greater
+than 128, as described above (@pxref{Signals}).
+Otherwise, the return status is the exit status
+of the last process or job waited for.
@item disown
@btindex disown
Suspend the execution of this shell until it receives a
@code{SIGCONT} signal.
-A login shell cannot be suspended; the @option{-f}
+A login shell,
+or a shell without job control enabled,
+cannot be suspended; the @option{-f}
option can be used to override this and force the suspension.
+The return status is 0 unless the shell is a login shell
+or job control is not enabled
+and
+@option{-f}
+is not supplied.
+
@end table
When job control is not active, the @code{kill} and @code{wait}
@item
Type @samp{make install} to install @code{bash} and @code{bashbug}.
-This will also install the manual pages and Info file.
+This will also install the manual pages and Info file, message translation
+files, some supplemental documentation, a number of example loadable
+builtin commands, and a set of header files for developing loadable
+builtins.
+You may need additional privileges to install @code{bash} to your
+desired destination, so @samp{sudo make install} might be required.
+More information about controlling the locations where @code{bash} and
+other files are installed is below (@pxref{Installation Names}).
@end enumerate
values for various system-dependent variables used during
compilation. It uses those values to create a @file{Makefile} in
each directory of the package (the top directory, the
-@file{builtins}, @file{doc}, and @file{support} directories,
+@file{builtins}, @file{doc}, @file{po}, and @file{support} directories,
each directory under @file{lib}, and several others). It also creates a
@file{config.h} file containing system-dependent definitions.
Finally, it creates a shell script named @code{config.status} that you
If you want to build Bash in a directory separate from the source
directory -- to build for multiple architectures, for example --
just use the full path to the configure script. The following commands
-will build bash in a directory under @file{/usr/local/build} from
+will build Bash in a directory under @file{/usr/local/build} from
the source code in @file{/usr/local/src/bash-4.4}:
@example
considered for the next release.
The file @file{configure.ac} is used to create @code{configure}
-by a program called Autoconf. You only need
-@file{configure.ac} if you want to change it or regenerate
-@code{configure} using a newer version of Autoconf. If
-you do this, make sure you are using Autoconf version 2.50 or
+by a program called Autoconf.
+You only need @file{configure.ac} if you want to change it or regenerate
+@code{configure} using a newer version of Autoconf.
+If you do this, make sure you are using Autoconf version 2.69 or
newer.
You can remove the program binaries and object files from the
source files are. @code{configure} automatically checks for the
source code in the directory that @code{configure} is in and in `..'.
-If you have to use a @code{make} that does not supports the @code{VPATH}
+If you have to use a @code{make} that does not support the @code{VPATH}
variable, you can compile Bash for one architecture at a
time in the source code directory. After you have installed
Bash for one architecture, use @samp{make distclean} before
@section Installation Names
By default, @samp{make install} will install into
-@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can
-specify an installation prefix other than @file{/usr/local} by
+@file{/usr/local/bin}, @file{/usr/local/man}, etc.;
+that is, the @dfn{installation prefix} defaults to @file{/usr/local}.
+You can specify an installation prefix other than @file{/usr/local} by
giving @code{configure} the option @option{--prefix=@var{PATH}},
-or by specifying a value for the @env{DESTDIR} @samp{make}
-variable when running @samp{make install}.
+or by specifying a value for the @env{prefix} @samp{make}
+variable when running @samp{make install}
+(e.g., @samp{make install prefix=@var{PATH}}).
+The @env{prefix} variable provides a default for @env{exec_prefix} and
+other variables used when installing Bash.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.
If you give @code{configure} the option
@option{--exec-prefix=@var{PATH}}, @samp{make install} will use
@var{PATH} as the prefix for installing programs and libraries.
-Documentation and other data files will still use the regular prefix.
+Documentation and other data files will still use the regular prefix.
+
+If you would like to change the installation locations for a single run,
+you can specify these variables as arguments to @code{make}:
+@samp{make install exec_prefix=/} will install @code{bash} and
+@code{bashbug} into @file{/bin} instead of the default @file{/usr/local/bin}.
+
+If you want to see the files Bash will install and where it will install
+them without changing anything on your system, specify the variable
+@env{DESTDIR} as an argument to @code{make}. Its value should be the
+absolute directory path you'd like to use as the root of your sample
+installation tree. For example,
+
+@example
+mkdir /fs1/bash-install
+make install DESTDIR=/fs1/bash-install
+@end example
+
+@noindent
+will install @code{bash} into @file{/fs1/bash-install/usr/local/bin/bash},
+the documentation into directories within
+@file{/fs1/bash-install/usr/local/share}, the example loadable builtins into
+@file{/fs1/bash-install/usr/local/lib/bash}, and so on.
+You can use the usual @env{exec_prefix} and @env{prefix} variables to alter
+the directory paths beneath the value of @env{DESTDIR}.
+
+The GNU Makefile standards provide a more complete description of these
+variables and their effects.
@node Specifying the System Type
@section Specifying the System Type
There may be some features @code{configure} can not figure out
-automatically, but need to determine by the type of host Bash
+automatically, but needs to determine by the type of host Bash
will run on. Usually @code{configure} can figure that
out, but if it prints a message saying it can not guess the host
type, give it the @option{--host=TYPE} option. @samp{TYPE} can
@item --with-libintl-prefix[=@var{PREFIX}]
Define this to make Bash link with a locally-installed version of the
-libintl library instead ofthe version in @file{lib/intl}.
+libintl library instead of the version in @file{lib/intl}.
@item --with-libiconv-prefix[=@var{PREFIX}]
Define this to make Bash look for libiconv in @var{PREFIX} instead of the
@table @code
@item --enable-largefile
-Enable support for @uref{http://www.unix.org/version2/whatsnew/lfs20mar.html,
+Enable support for @url{http://www.unix.org/version2/whatsnew/lfs20mar.html,
large files} if the operating system requires special compiler options
to build programs which can access large files. This is enabled by
default, if the operating system provides large file support.
the following options, but it is processed first, so individual
options may be enabled using @samp{enable-@var{feature}}.
-All of the following options except for @samp{disabled-builtins},
+All of the following options except for
+@samp{alt-array-implementation},
+@samp{disabled-builtins},
@samp{direxpand-default},
@samp{strict-posix-default},
and
Allow alias expansion and include the @code{alias} and @code{unalias}
builtins (@pxref{Aliases}).
+@item --enable-alt-array-implementation
+This builds Bash using an alternate implementation of arrays
+(@pxref{Arrays}) that provides faster access at the expense of using
+more memory (sometimes many times more, depending on how sparse an array is).
+
@item --enable-arith-for-command
Include support for the alternate form of the @code{for} command
that behaves like the C language @code{for} statement
(@pxref{Pipelines}).
@item --enable-debugger
-Include support for the bash debugger (distributed separately).
+Include support for the Bash debugger (distributed separately).
@item --enable-dev-fd-stat-broken
If calling @code{stat} on /dev/fd/@var{N} returns different results than
@item --enable-strict-posix-default
Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}).
+@item --enable-translatable-strings
+Enable support for @code{$"@var{string}"} translatable strings
+(@pxref{Locale Translation}).
+
@item --enable-usg-echo-default
A synonym for @code{--enable-xpg-echo-default}.
make sure that it really is a bug, and that it appears in the latest
version of Bash.
The latest version of Bash is always available for FTP from
-@uref{ftp://ftp.gnu.org/pub/gnu/bash/}.
+@uref{ftp://ftp.gnu.org/pub/gnu/bash/} and from
+@uref{http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz}.
Once you have determined that a bug actually exists, use the
-@code{bashbug} command to submit a bug report.
-If you have a fix, you are encouraged to mail that as well!
+@code{bashbug} command to submit a bug report or use the form at the
+@uref{https://savannah.gnu.org/projects/bash/,Bash project page}.
+If you have a fix, you are encouraged to submit that as well!
Suggestions and `philosophical' bug reports may be mailed
-to @email{bug-bash@@gnu.org} or posted to the Usenet
-newsgroup @code{gnu.bash.bug}.
+to @email{bug-bash@@gnu.org} or @email{help-bash@@gnu.org}.
All bug reports should include:
@itemize @bullet
@item
Bash includes the @code{caller} builtin, which displays the context of
any active subroutine call (a shell function or a script executed with
-the @code{.} or @code{source} builtins). This supports the bash
+the @code{.} or @code{source} builtins). This supports the Bash
debugger.
@item
The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a
@code{RETURN} pseudo-signal specification, similar to
@code{EXIT} and @code{DEBUG}.
-Commands specified with an @code{RETURN} trap are executed before
+Commands specified with a @code{RETURN} trap are executed before
execution resumes after a shell function or a shell script executed with
@code{.} or @code{source} returns.
The @code{RETURN} trap is not inherited by shell functions unless the
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