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documentation updates for arithmetic expansion and array subscripts; update BASH_COMMAND for subshells; fix potential file descriptor leak in here document pipes

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Chet Ramey
2025-03-07 10:23:58 -05:00
parent e608233770
commit c3997d51f8
36 changed files with 19690 additions and 19094 deletions
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doc/bashref.html
+104 -25
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@@ -4,9 +4,9 @@
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<!-- This text is a brief description of the features that are present in
the Bash shell (version 5.3, 8 January 2025).
the Bash shell (version 5.3, 24 February 2025).
This is Edition 5.3, last updated 8 January 2025,
This is Edition 5.3, last updated 24 February 2025,
of The GNU Bash Reference Manual,
for Bash, Version 5.3.
@@ -77,10 +77,10 @@ Next: <a href="#Introduction" accesskey="n" rel="next">Introduction</a>, Previou
<h1 class="top" id="Bash-Features-1"><span>Bash Features<a class="copiable-link" href="#Bash-Features-1"> &para;</a></span></h1>
<p>This text is a brief description of the features that are present in
the Bash shell (version 5.3, 8 January 2025).
the Bash shell (version 5.3, 24 February 2025).
The Bash home page is <a class="url" href="http://www.gnu.org/software/bash/">http://www.gnu.org/software/bash/</a>.
</p>
<p>This is Edition 5.3, last updated 8 January 2025,
<p>This is Edition 5.3, last updated 24 February 2025,
of <cite class="cite">The GNU Bash Reference Manual</cite>,
for <code class="code">Bash</code>, Version 5.3.
</p>
@@ -1490,8 +1490,11 @@ done
described below (see <a class="pxref" href="#Shell-Arithmetic">Shell Arithmetic</a>).
The <var class="var">expression</var> undergoes the same expansions
as if it were within double quotes,
but double quote characters in <var class="var">expression</var> are not treated specially
and are removed.
but unescaped double quote characters
in <var class="var">expression</var> are not treated
specially and are removed.
Since this can potentially result in empty strings,
this command treats those as expressions that evaluate to 0.
If the value of the expression is non-zero, the return status is 0;
otherwise the return status is 1.
</p>
@@ -2124,7 +2127,7 @@ The null string is a valid value.
Once a variable is set, it may be unset only by using
the <code class="code">unset</code> builtin command.
</p>
<p>A variable may be assigned to by a statement of the form
<p>A variable is assigned to using a statement of the form
</p><div class="example">
<pre class="example-preformatted"><var class="var">name</var>=[<var class="var">value</var>]
</pre></div>
@@ -2460,7 +2463,7 @@ each generated term will contain the same number of digits,
zero-padding where necessary.
When letters are supplied, the expression expands to each character
lexicographically between <var class="var">x</var> and <var class="var">y</var>, inclusive,
using the default C locale.
using the C locale.
Note that both <var class="var">x</var> and <var class="var">y</var> must be of the same type
(integer or letter).
When the increment is supplied, it is used as the difference between
@@ -2729,6 +2732,14 @@ $ : ${var=DEFAULT}
$ echo $var
DEFAULT
$ var=
$ : ${var=DEFAULT}
$ echo $var
$ var=
$ : ${var:=DEFAULT}
$ echo $var
DEFAULT
$ unset var
$ : ${var:=DEFAULT}
$ echo $var
DEFAULT
@@ -2750,6 +2761,16 @@ Otherwise, the value of <var class="var">parameter</var> is substituted.
<pre class="example-preformatted">$ var=
$ : ${var:?var is unset or null}
bash: var: var is unset or null
$ echo ${var?var is unset}
$ unset var
$ : ${var?var is unset}
bash: var: var is unset
$ : ${var:?var is unset or null}
bash: var: var is unset or null
$ var=123
$ echo ${var:?var is unset or null}
123
</pre></div>
</dd>
@@ -2763,9 +2784,18 @@ The value of <var class="var">parameter</var> is not used.
<pre class="example-preformatted">$ var=123
$ echo ${var:+var is set and not null}
var is set and not null
$ echo ${var+var is set}
var is set
$ var=
$ echo ${var:+var is set and not null}
$ echo ${var+var is set}
var is set
$ unset var
$ echo ${var+var is set}
$ echo ${var:+var is set and not null}
$
</pre></div>
@@ -2778,9 +2808,15 @@ starting at the character specified by <var class="var">offset</var>.
If <var class="var">parameter</var> is &lsquo;<samp class="samp">@</samp>&rsquo; or &lsquo;<samp class="samp">*</samp>&rsquo;, an indexed array subscripted by
&lsquo;<samp class="samp">@</samp>&rsquo; or &lsquo;<samp class="samp">*</samp>&rsquo;, or an associative array name, the results differ as
described below.
If <var class="var">length</var> is omitted, it expands to the substring of the value of
If :<var class="var">length</var> is omitted (the first form above), this
expands to the substring of the value of
<var class="var">parameter</var> starting at the character specified by <var class="var">offset</var>
and extending to the end of the value.
If <var class="var">offset</var> is omitted,
it is treated as 0.
If <var class="var">length</var> is omitted,
but the colon after <var class="var">offset</var> is present,
it is treated as 0.
<var class="var">length</var> and <var class="var">offset</var> are arithmetic expressions
(see <a class="pxref" href="#Shell-Arithmetic">Shell Arithmetic</a>).
</p>
@@ -3320,11 +3356,16 @@ The format for arithmetic expansion is:
<p>The <var class="var">expression</var> undergoes the same expansions
as if it were within double quotes,
but double quote characters in <var class="var">expression</var> are not treated specially
and are removed.
but unescaped double quote characters
in <var class="var">expression</var> 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.
Since the way Bash handles double quotes
can potentially result in empty strings,
arithmetic expansion treats
those as expressions that evaluate to 0.
Arithmetic expansions may be nested.
</p>
<p>The evaluation is performed according to the rules listed below
@@ -5270,7 +5311,8 @@ command), a list, or a compound command returns a
non-zero exit status,
subject to the following conditions.
The <code class="code">ERR</code> trap is not executed if the failed command is part of the
command list immediately following an <code class="code">until</code> or <code class="code">while</code> keyword,
command list immediately following an
<code class="code">until</code> or <code class="code">while</code> reserved word,
part of the test following the <code class="code">if</code> or <code class="code">elif</code> reserved words,
part of a command executed in a <code class="code">&amp;&amp;</code> or <code class="code">||</code> list
except the command following the final <code class="code">&amp;&amp;</code> or <code class="code">||</code>,
@@ -6507,7 +6549,8 @@ a list (see <a class="pxref" href="#Lists">Lists of Commands</a>),
or a compound command (see <a class="pxref" href="#Compound-Commands">Compound Commands</a>)
returns a non-zero status.
The shell does not exit if the command that fails is part of the
command list immediately following a <code class="code">while</code> or <code class="code">until</code> keyword,
command list immediately following a
<code class="code">while</code> or <code class="code">until</code> reserved word,
part of the test in an <code class="code">if</code> statement,
part of any command executed in a <code class="code">&amp;&amp;</code> or <code class="code">||</code> list except
the command following the final <code class="code">&amp;&amp;</code> or <code class="code">||</code>,
@@ -9280,6 +9323,11 @@ respectively. <var class="var">Arg1</var> and <var class="var">arg2</var>
may be positive or negative integers.
When used with the <code class="code">[[</code> command, <var class="var">arg1</var> and <var class="var">arg2</var>
are evaluated as arithmetic expressions (see <a class="pxref" href="#Shell-Arithmetic">Shell Arithmetic</a>).
Since the expansions the <code class="code">[[</code> command performs on
<var class="var">arg1</var> and <var class="var">arg2</var>
can potentially result in empty strings,
arithmetic expression evaluation treats
those as expressions that evaluate to 0.
</p></dd>
</dl>
@@ -9536,8 +9584,24 @@ and are zero-based;
associative arrays use arbitrary strings.
Unless otherwise noted, indexed array indices must be non-negative integers.
</p>
<p>An indexed array is created automatically if any variable is assigned to
using the syntax
<p>The shell performs
parameter and variable expansion, arithmetic expansion,
command substitution, and quote removal
on indexed array subscripts.
Since this
can potentially result in empty strings,
subscript indexing treats
those as expressions that evaluate to 0.
</p>
<p>The shell performs
tilde expansion,
parameter and variable expansion, arithmetic expansion,
command substitution, and quote removal
on associative array subscripts.
Empty strings cannot be used as associative array keys.
</p>
<p>Bash automatically creates an indexed array
if any variable is assigned to using the syntax
</p><div class="example">
<pre class="example-preformatted"><var class="var">name</var>[<var class="var">subscript</var>]=<var class="var">value</var>
</pre></div>
@@ -10268,7 +10332,7 @@ default value the shell assigns to <code class="env">$HISTFILE</code>).
double-quoted string, even if the <code class="code">histexpand</code> option is enabled.
</li><li> When printing shell function definitions (e.g., by <code class="code">type</code>), Bash does
not print the <code class="code">function</code> keyword unless necessary.
not print the <code class="code">function</code> reserved word unless necessary.
</li><li> Non-interactive shells exit if a syntax error in an arithmetic expansion
results in an invalid expression.
@@ -10382,6 +10446,12 @@ separated by spaces, without the &lsquo;<samp class="samp">SIG</samp>&rsquo; pre
</li><li> The <code class="code">kill</code> builtin does not accept signal names with a &lsquo;<samp class="samp">SIG</samp>&rsquo;
prefix.
</li><li> The <code class="code">kill</code> builtin returns a failure status if any of the pid or job
arguments are invalid or if sending the specified signal to any of them
fails.
In default mode, <code class="code">kill</code> returns success if the signal was
successfully sent to any of the specified processes.
</li><li> The <code class="code">printf</code> builtin uses <code class="code">double</code> (via <code class="code">strtod</code>) to convert
arguments corresponding to floating point conversion specifiers, instead of
<code class="code">long double</code> if it&rsquo;s available.
@@ -10750,7 +10820,10 @@ Bash uses the <var class="var">job</var> abstraction as the basis for job contro
each process has a <em class="dfn">process group <small class="sc">ID</small></em>, and
the operating system maintains the notion of a current terminal
process group <small class="sc">ID</small>.
Processes that have the same process group ID are said to be part of
This terminal process group <small class="sc">ID</small> is associated with the
<em class="dfn">controlling terminal</em>.
</p>
<p>Processes that have the same process group ID are said to be part of
the same <em class="dfn">process group</em>.
Members of the foreground process group (processes whose
process group <small class="sc">ID</small> is equal to the current terminal process group
@@ -10758,14 +10831,18 @@ process group <small class="sc">ID</small> is equal to the current terminal proc
Processes in the foreground process group are said to be
foreground processes.
Background processes
are those whose process group <small class="sc">ID</small> differs from the terminal&rsquo;s;
are those whose process group <small class="sc">ID</small> differs from the
controlling terminal&rsquo;s;
such processes are immune to keyboard-generated signals.
Only foreground processes are allowed to read from or, if
the user so specifies with <code class="code">stty tostop</code>, write to the terminal.
Background processes which attempt to
read from (write to when <code class="code">tostop</code> is in effect) the
terminal are sent a <code class="code">SIGTTIN</code> (<code class="code">SIGTTOU</code>)
signal by the kernel&rsquo;s terminal driver,
Only foreground processes are allowed to read from or,
if the user so specifies with
<code class="code">stty tostop</code>,
write to the controlling terminal.
The system sends a
<code class="code">SIGTTIN</code> (<code class="code">SIGTTOU</code>)
signal to background processes which attempt to
read from (write to when <code class="code">tostop</code> is in effect)
the terminal,
which, unless caught, suspends the process.
</p>
<p>If the operating system on which Bash is running supports
@@ -12578,6 +12655,8 @@ leaving the current line at the top of the screen.
<dd><p>Clear the screen,
then redraw the current line,
leaving the current line at the top of the screen.
If given a numeric argument, this refreshes the current line
without clearing the screen.
</p>
</dd>
<dt><a id="index-redraw_002dcurrent_002dline-_0028_0029"></a><span><code class="code">redraw-current-line ()</code><a class="copiable-link" href="#index-redraw_002dcurrent_002dline-_0028_0029"> &para;</a></span></dt>
@@ -15607,7 +15686,7 @@ expansion (see <a class="pxref" href="#Tilde-Expansion">Tilde Expansion</a>).
</li><li>Bash implements command aliases and the <code class="code">alias</code> and <code class="code">unalias</code>
builtins (see <a class="pxref" href="#Aliases">Aliases</a>).
</li><li>Bash implements the <code class="code">!</code> keyword to negate the return value of
</li><li>Bash implements the <code class="code">!</code> reserved word to negate the return value of
a pipeline (see <a class="pxref" href="#Pipelines">Pipelines</a>).
This is very useful when an <code class="code">if</code> statement needs to act only if a
test fails.