194 lines
8.7 KiB
HTML
194 lines
8.7 KiB
HTML
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<head>
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<title>Debugging with GDB: Conditional Init Constructs</title>
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Readline-Init-File.html#Readline-Init-File" rel="up" title="Readline Init File">
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<link href="Sample-Init-File.html#Sample-Init-File" rel="next" title="Sample Init File">
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<a name="Conditional-Init-Constructs"></a>
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<div class="header">
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<p>
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Next: <a href="Sample-Init-File.html#Sample-Init-File" accesskey="n" rel="next">Sample Init File</a>, Previous: <a href="Readline-Init-File-Syntax.html#Readline-Init-File-Syntax" accesskey="p" rel="previous">Readline Init File Syntax</a>, Up: <a href="Readline-Init-File.html#Readline-Init-File" accesskey="u" rel="up">Readline Init File</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Conditional-Init-Constructs-1"></a>
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<h4 class="subsection">32.3.2 Conditional Init Constructs</h4>
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<p>Readline implements a facility similar in spirit to the conditional
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compilation features of the C preprocessor which allows key
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bindings and variable settings to be performed as the result
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of tests. There are four parser directives used.
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</p>
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<dl compact="compact">
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<dt><code>$if</code></dt>
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<dd><p>The <code>$if</code> construct allows bindings to be made based on the
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editing mode, the terminal being used, or the application using
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Readline. The text of the test, after any comparison operator,
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extends to the end of the line;
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unless otherwise noted, no characters are required to isolate it.
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</p>
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<dl compact="compact">
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<dt><code>mode</code></dt>
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<dd><p>The <code>mode=</code> form of the <code>$if</code> directive is used to test
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whether Readline is in <code>emacs</code> or <code>vi</code> mode.
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This may be used in conjunction
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with the ‘<samp>set keymap</samp>’ command, for instance, to set bindings in
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the <code>emacs-standard</code> and <code>emacs-ctlx</code> keymaps only if
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Readline is starting out in <code>emacs</code> mode.
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</p>
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</dd>
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<dt><code>term</code></dt>
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<dd><p>The <code>term=</code> form may be used to include terminal-specific
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key bindings, perhaps to bind the key sequences output by the
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terminal’s function keys. The word on the right side of the
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‘<samp>=</samp>’ is tested against both the full name of the terminal and
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the portion of the terminal name before the first ‘<samp>-</samp>’. This
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allows <code>sun</code> to match both <code>sun</code> and <code>sun-cmd</code>,
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for instance.
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</p>
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</dd>
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<dt><code>version</code></dt>
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<dd><p>The <code>version</code> test may be used to perform comparisons against
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specific Readline versions.
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The <code>version</code> expands to the current Readline version.
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The set of comparison operators includes
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‘<samp>=</samp>’ (and ‘<samp>==</samp>’), ‘<samp>!=</samp>’, ‘<samp><=</samp>’, ‘<samp>>=</samp>’, ‘<samp><</samp>’,
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and ‘<samp>></samp>’.
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The version number supplied on the right side of the operator consists
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of a major version number, an optional decimal point, and an optional
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minor version (e.g., ‘<samp>7.1</samp>’). If the minor version is omitted, it
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is assumed to be ‘<samp>0</samp>’.
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The operator may be separated from the string <code>version</code> and
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from the version number argument by whitespace.
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The following example sets a variable if the Readline version being used
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is 7.0 or newer:
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</p><div class="example">
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<pre class="example">$if version >= 7.0
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set show-mode-in-prompt on
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$endif
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</pre></div>
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</dd>
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<dt><code>application</code></dt>
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<dd><p>The <var>application</var> construct is used to include
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application-specific settings. Each program using the Readline
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library sets the <var>application name</var>, and you can test for
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a particular value.
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This could be used to bind key sequences to functions useful for
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a specific program. For instance, the following command adds a
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key sequence that quotes the current or previous word in Bash:
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</p><div class="example">
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<pre class="example">$if Bash
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# Quote the current or previous word
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"\C-xq": "\eb\"\ef\""
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$endif
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</pre></div>
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</dd>
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<dt><code>variable</code></dt>
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<dd><p>The <var>variable</var> construct provides simple equality tests for Readline
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variables and values.
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The permitted comparison operators are ‘<samp>=</samp>’, ‘<samp>==</samp>’, and ‘<samp>!=</samp>’.
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The variable name must be separated from the comparison operator by
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whitespace; the operator may be separated from the value on the right hand
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side by whitespace.
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Both string and boolean variables may be tested. Boolean variables must be
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tested against the values <var>on</var> and <var>off</var>.
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The following example is equivalent to the <code>mode=emacs</code> test described
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above:
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</p><div class="example">
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<pre class="example">$if editing-mode == emacs
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set show-mode-in-prompt on
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$endif
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</pre></div>
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</dd>
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</dl>
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</dd>
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<dt><code>$endif</code></dt>
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<dd><p>This command, as seen in the previous example, terminates an
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<code>$if</code> command.
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</p>
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</dd>
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<dt><code>$else</code></dt>
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<dd><p>Commands in this branch of the <code>$if</code> directive are executed if
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the test fails.
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</p>
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</dd>
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<dt><code>$include</code></dt>
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<dd><p>This directive takes a single filename as an argument and reads commands
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and bindings from that file.
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For example, the following directive reads from <samp>/etc/inputrc</samp>:
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</p><div class="example">
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<pre class="example">$include /etc/inputrc
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</pre></div>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Sample-Init-File.html#Sample-Init-File" accesskey="n" rel="next">Sample Init File</a>, Previous: <a href="Readline-Init-File-Syntax.html#Readline-Init-File-Syntax" accesskey="p" rel="previous">Readline Init File Syntax</a>, Up: <a href="Readline-Init-File.html#Readline-Init-File" accesskey="u" rel="up">Readline Init File</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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