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complete initial implementation of nofork command substitution (${ command; })

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Chet Ramey
2023-05-15 13:30:18 -04:00
parent c375f8f45f
commit e44e3d50de
42 changed files with 4387 additions and 3516 deletions
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doc/bashref.html
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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 5.2, 17 April 2023).
the Bash shell (version 5.2, 14 May 2023).
This is Edition 5.2, last updated 17 April 2023,
This is Edition 5.2, last updated 14 May 2023,
of The GNU Bash Reference Manual,
for Bash, Version 5.2.
@@ -77,10 +77,10 @@ Next: <a href="#Introduction" accesskey="n" rel="next">Introduction</a>, Previou
<span id="Bash-Features-1"></span><h1 class="top">Bash Features</h1>
<p>This text is a brief description of the features that are present in
the Bash shell (version 5.2, 17 April 2023).
the Bash shell (version 5.2, 14 May 2023).
The Bash home page is <a href="http://www.gnu.org/software/bash/">http://www.gnu.org/software/bash/</a>.
</p>
<p>This is Edition 5.2, last updated 17 April 2023,
<p>This is Edition 5.2, last updated 14 May 2023,
of <cite>The GNU Bash Reference Manual</cite>,
for <code>Bash</code>, Version 5.2.
</p>
@@ -737,8 +737,8 @@ Next: <a href="#Locale-Translation" accesskey="n" rel="next">Locale-Specific Tra
<span id="ANSI_002dC-Quoting-1"></span><h4 class="subsubsection">3.1.2.4 ANSI-C Quoting</h4>
<span id="index-quoting_002c-ANSI"></span>
<p>Character sequences of the form $&rsquo;<var>string</var>&rsquo; are treated as a special
kind of single quotes.
<p>Character sequences of the form <code>$'<var>string</var>'</code> are treated as
a special kind of single quotes.
The sequence expands to <var>string</var>, with backslash-escaped characters
in <var>string</var> replaced as specified by the ANSI C standard.
Backslash escape sequences, if present, are decoded as follows:
@@ -3049,24 +3049,25 @@ Next: <a href="#Arithmetic-Expansion" accesskey="n" rel="next">Arithmetic Expans
<p>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:
</p><div class="example">
<pre class="example">$(<var>command</var>)
</pre></div>
<p>or
<p>or (deprecated)
</p><div class="example">
<pre class="example">`<var>command</var>`
<pre class="example">`<var>command</var>`.
</pre></div>
<p>Bash performs the expansion by executing <var>command</var> in a subshell environment
and replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
<p>Bash performs the expansion by executing <var>command</var> in a subshell
environment and replacing the command substitution with the standard
output of the command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution <code>$(cat <var>file</var>)</code> can be
replaced by the equivalent but faster <code>$(&lt; <var>file</var>)</code>.
</p>
<p>When the old-style backquote form of substitution is used,
<p>With the old-style backquote form of substitution,
backslash retains its literal meaning except when followed by
&lsquo;<samp>$</samp>&rsquo;, &lsquo;<samp>`</samp>&rsquo;, or &lsquo;<samp>\</samp>&rsquo;.
The first backquote not preceded by a backslash terminates the
@@ -3074,11 +3075,70 @@ command substitution.
When using the <code>$(<var>command</var>)</code> form, all characters between
the parentheses make up the command; none are treated specially.
</p>
<p>There is an alternate form of command substitution:
</p>
<div class="example">
<pre class="example">${<var>C</var> <var>command</var>; }
</pre></div>
<p>which executes <var>command</var> in the current execution environment.
This means that side effects of <var>command</var> take effect immediately
in the current execution environment and persist in the current
environment after the command completes (e.g., the <code>exit</code> builtin
will exit the shell).
</p>
<p>The character <var>C</var> following the open brace must be a space, tab,
newline, &lsquo;<samp>(</samp>&rsquo;, or &lsquo;<samp>|</samp>&rsquo;, 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.
</p>
<p>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</code> builtin forces
<var>command</var> to complete;
however, the rest of the execution environment,
including the positional parameters, is shared with the caller.
</p>
<p>If the first character following the open brace is a &lsquo;<samp>(</samp>&rsquo;,
<var>command</var> is executed in a subshell, and <var>command</var> must be
terminated by a &lsquo;<samp>)</samp>&rsquo;. This is similar to the <code>(</code> compound
command (see <a href="#Command-Grouping">Grouping Commands</a>).
If the first character is a &lsquo;<samp>|</samp>&rsquo;, the construct expands to the
value of the <code>REPLY</code> shell variable after <var>command</var> executes,
without removing any trailing newlines,
and the standard output of <var>command</var> remains the same as in the
calling shell.
Bash creates <code>REPLY</code> as an initially-unset local variable when
<var>command</var> executes, and restores <code>REPLY</code> to the value it had
before the command substitution after <var>command</var> completes,
as with any local variable.
</p>
<p>For example, this construct expands to &lsquo;<samp>12345</samp>&rsquo;, and leaves the
shell variable <code>X</code> unchanged in the current execution environment:
</p>
<div class="example">
<pre class="example">${ local X=12345 ; echo $X; }
</pre></div>
<p>(not declaring <code>X</code> as local would modify its value in the current
environment, as with normal shell function execution),
while this construct does not require any output to expand to
&lsquo;<samp>12345</samp>&rsquo;:
</p>
<div class="example">
<pre class="example">${| REPLY=12345; }
</pre></div>
<p>and restores <code>REPLY</code> to the value it had before the command substitution.
</p>
<p>Command substitutions may be nested. To nest when using the backquoted
form, escape the inner backquotes with backslashes.
</p>
<p>If the substitution appears within double quotes, word splitting and
filename expansion are not performed on the results.
<p>If the substitution appears within double quotes, Bash does not perform
word splitting and filename expansion on the results.
</p>
<hr>
</div>
@@ -7294,6 +7354,9 @@ inode change time, and number of blocks, respectively.
<p>For example, a value of <code>-mtime</code> sorts the results in descending
order by modification time (newest first).
</p>
<p>A sort specifier of &lsquo;<samp>nosort</samp>&rsquo; disables sorting completely; the results
are returned in the order they are read from the file system,.
</p>
<p>If the sort specifier is missing, it defaults to <var>name</var>,
so a value of &lsquo;<samp>+</samp>&rsquo; is equivalent to the null string,
and a value of &lsquo;<samp>-</samp>&rsquo; sorts by name in descending order.
@@ -9655,16 +9718,6 @@ and it is required for bash-5.1 and later versions.
has no special effect
</li></ul>
</dd>
<dt><span><code>compat32</code></span></dt>
<dd><ul>
<li> interrupting a command list such as &quot;a ; b ; c&quot; 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)
</li></ul>
</dd>
<dt><span><code>compat40</code></span></dt>
<dd><ul>