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<title>Commands In Guile - Debugging with GDB</title>
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<div class="node">
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<a name="Commands-In-Guile"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Parameters-In-Guile.html#Parameters-In-Guile">Parameters In Guile</a>,
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Previous: <a rel="previous" accesskey="p" href="Writing-a-Guile-Pretty_002dPrinter.html#Writing-a-Guile-Pretty_002dPrinter">Writing a Guile Pretty-Printer</a>,
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Up: <a rel="up" accesskey="u" href="Guile-API.html#Guile-API">Guile API</a>
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<hr>
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</div>
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<h5 class="subsubsection">23.3.3.11 Commands In Guile</h5>
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<p><a name="index-commands-in-guile-2606"></a><a name="index-guile-commands-2607"></a>You can implement new <span class="sc">gdb</span> CLI commands in Guile. A CLI
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command object is created with the <code>make-command</code> Guile function,
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and added to <span class="sc">gdb</span> with the <code>register-command!</code> Guile function.
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This two-step approach is taken to separate out the side-effect of adding
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the command to <span class="sc">gdb</span> from <code>make-command</code>.
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<p>There is no support for multi-line commands, that is commands that
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consist of multiple lines and are terminated with <code>end</code>.
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<!-- TODO: line length -->
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<div class="defun">
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— Scheme Procedure: <b>(</b><var>make-command name </var><span class="roman">[</span><var>#:invoke invoke</var>] <span class="roman">[</span><var>#:command-class command-class</var><span class="roman">]</span> <span class="roman">[</span><var>#:completer-class completer</var>] <span class="roman">[</span><var>#:prefix? prefix</var><span class="roman">]</span> <span class="roman">[</span><var>#:doc doc-string</var>])<var><a name="index-g_t_0028-2608"></a></var><br>
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<blockquote>
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<p>The argument <var>name</var> is the name of the command. If <var>name</var> consists of
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multiple words, then the initial words are looked for as prefix
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commands. In this case, if one of the prefix commands does not exist,
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an exception is raised.
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<p>The result is the <code><gdb:command></code> object representing the command.
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The command is not usable until it has been registered with <span class="sc">gdb</span>
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with <code>register-command!</code>.
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<p>The rest of the arguments are optional.
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<p>The argument <var>invoke</var> is a procedure of three arguments: <var>self</var>,
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<var>args</var> and <var>from-tty</var>. The argument <var>self</var> is the
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<code><gdb:command></code> object representing the command.
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The argument <var>args</var> is a string representing the arguments passed to
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the command, after leading and trailing whitespace has been stripped.
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The argument <var>from-tty</var> is a boolean flag and specifies whether the
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command should consider itself to have been originated from the user
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invoking it interactively. If this function throws an exception,
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it is turned into a <span class="sc">gdb</span> <code>error</code> call.
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Otherwise, the return value is ignored.
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<p>The argument <var>command-class</var> is one of the ‘<samp><span class="samp">COMMAND_</span></samp>’ constants
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defined below. This argument tells <span class="sc">gdb</span> how to categorize the
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new command in the help system. The default is <code>COMMAND_NONE</code>.
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<p>The argument <var>completer</var> is either <code>#f</code>, one of the ‘<samp><span class="samp">COMPLETE_</span></samp>’
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constants defined below, or a procedure, also defined below.
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This argument tells <span class="sc">gdb</span> how to perform completion
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for this command. If not provided or if the value is <code>#f</code>,
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then no completion is performed on the command.
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<p>The argument <var>prefix</var> is a boolean flag indicating whether the new
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command is a prefix command; sub-commands of this command may be
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registered.
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<p>The argument <var>doc-string</var> is help text for the new command.
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If no documentation string is provided, the default value “This command is
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not documented.” is used.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>register-command!</b><var> command<a name="index-register_002dcommand_0021-2609"></a></var><br>
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<blockquote><p>Add <var>command</var>, a <code><gdb:command></code> object, to <span class="sc">gdb</span>'s
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list of commands.
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It is an error to register a command more than once.
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The result is unspecified.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>command?</b><var> object<a name="index-command_003f-2610"></a></var><br>
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<blockquote><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:command></code> object.
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Otherwise return <code>#f</code>.
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</p></blockquote></div>
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<p><a name="index-don_0027t-repeat-Guile-command-2611"></a>
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<div class="defun">
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— Scheme Procedure: <b>dont-repeat</b><var><a name="index-dont_002drepeat-2612"></a></var><br>
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<blockquote><p>By default, a <span class="sc">gdb</span> command is repeated when the user enters a
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blank line at the command prompt. A command can suppress this
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behavior by invoking the <code>dont-repeat</code> function. This is similar
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to the user command <code>dont-repeat</code>, see <a href="Define.html#Define">dont-repeat</a>.
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</p></blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>string->argv</b><var> string<a name="index-string_002d_003eargv-2613"></a></var><br>
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<blockquote><p>Convert a string to a list of strings split up according to
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<span class="sc">gdb</span>'s argv parsing rules.
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It is recommended to use this for consistency.
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Arguments are separated by spaces and may be quoted.
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Example:
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<pre class="smallexample"> scheme@(guile-user)> (string->argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"")
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$1 = ("1" "2 \"3" "4 \"5" "6 '7")
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</pre>
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</blockquote></div>
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<div class="defun">
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— Scheme Procedure: <b>throw-user-error</b><var> message . args<a name="index-throw_002duser_002derror-2614"></a></var><br>
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<blockquote><p>Throw a <code>gdb:user-error</code> exception.
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The argument <var>message</var> is the error message as a format string, like the
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<var>fmt</var> argument to the <code>format</code> Scheme function.
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See <a href="../guile/Formatted-Output.html#Formatted-Output">Formatted Output</a>.
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The argument <var>args</var> is a list of the optional arguments of <var>message</var>.
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<p>This is used when the command detects a user error of some kind,
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say a bad command argument.
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<pre class="smallexample"> (gdb) guile (use-modules (gdb))
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(gdb) guile
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(register-command! (make-command "test-user-error"
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#:command-class COMMAND_OBSCURE
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#:invoke (lambda (self arg from-tty)
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(throw-user-error "Bad argument ~a" arg))))
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end
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(gdb) test-user-error ugh
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ERROR: Bad argument ugh
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</pre>
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</blockquote></div>
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<p><a name="index-completion-of-Guile-commands-2615"></a>
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<div class="defun">
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— completer: <b>self</b><var> text word<a name="index-self-2616"></a></var><br>
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<blockquote><p>If the <var>completer</var> option to <code>make-command</code> is a procedure,
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it takes three arguments: <var>self</var> which is the <code><gdb:command></code>
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object, and <var>text</var> and <var>word</var> which are both strings.
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The argument <var>text</var> holds the complete command line up to the cursor's
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location. The argument <var>word</var> holds the last word of the command line;
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this is computed using a word-breaking heuristic.
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<p>All forms of completion are handled by this function, that is,
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the <TAB> and <M-?> key bindings (see <a href="Completion.html#Completion">Completion</a>),
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and the <code>complete</code> command (see <a href="Help.html#Help">complete</a>).
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<p>This procedure can return several kinds of values:
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<ul>
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<li>If the return value is a list, the contents of the list are used as the
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completions. It is up to <var>completer</var> to ensure that the
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contents actually do complete the word. An empty list is
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allowed, it means that there were no completions available. Only
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string elements of the list are used; other elements in the
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list are ignored.
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<li>If the return value is a <code><gdb:iterator></code> object, it is iterated over to
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obtain the completions. It is up to <code>completer-procedure</code> to ensure
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that the results actually do complete the word. Only
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string elements of the result are used; other elements in the
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sequence are ignored.
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<li>All other results are treated as though there were no available
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completions.
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</ul>
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</p></blockquote></div>
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<p>When a new command is registered, it will have been declared as a member of
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some general class of commands. This is used to classify top-level
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commands in the on-line help system; note that prefix commands are not
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listed under their own category but rather that of their top-level
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command. The available classifications are represented by constants
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defined in the <code>gdb</code> module:
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<dl>
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<dt><code>COMMAND_NONE</code><a name="index-COMMAND_005fNONE-2617"></a><dd>The command does not belong to any particular class. A command in
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this category will not be displayed in any of the help categories.
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This is the default.
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<br><dt><code>COMMAND_RUNNING</code><a name="index-COMMAND_005fRUNNING-2618"></a><dd>The command is related to running the inferior. For example,
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<code>start</code>, <code>step</code>, and <code>continue</code> are in this category.
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Type <kbd>help running</kbd> at the <span class="sc">gdb</span> prompt to see a list of
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commands in this category.
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<br><dt><code>COMMAND_DATA</code><a name="index-COMMAND_005fDATA-2619"></a><dd>The command is related to data or variables. For example,
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<code>call</code>, <code>find</code>, and <code>print</code> are in this category. Type
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<kbd>help data</kbd> at the <span class="sc">gdb</span> prompt to see a list of commands
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in this category.
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<br><dt><code>COMMAND_STACK</code><a name="index-COMMAND_005fSTACK-2620"></a><dd>The command has to do with manipulation of the stack. For example,
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<code>backtrace</code>, <code>frame</code>, and <code>return</code> are in this
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category. Type <kbd>help stack</kbd> at the <span class="sc">gdb</span> prompt to see a
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list of commands in this category.
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<br><dt><code>COMMAND_FILES</code><a name="index-COMMAND_005fFILES-2621"></a><dd>This class is used for file-related commands. For example,
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<code>file</code>, <code>list</code> and <code>section</code> are in this category.
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Type <kbd>help files</kbd> at the <span class="sc">gdb</span> prompt to see a list of
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commands in this category.
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<br><dt><code>COMMAND_SUPPORT</code><a name="index-COMMAND_005fSUPPORT-2622"></a><dd>This should be used for “support facilities”, generally meaning
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things that are useful to the user when interacting with <span class="sc">gdb</span>,
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but not related to the state of the inferior. For example,
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<code>help</code>, <code>make</code>, and <code>shell</code> are in this category. Type
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<kbd>help support</kbd> at the <span class="sc">gdb</span> prompt to see a list of
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commands in this category.
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<br><dt><code>COMMAND_STATUS</code><a name="index-COMMAND_005fSTATUS-2623"></a><dd>The command is an ‘<samp><span class="samp">info</span></samp>’-related command, that is, related to the
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state of <span class="sc">gdb</span> itself. For example, <code>info</code>, <code>macro</code>,
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and <code>show</code> are in this category. Type <kbd>help status</kbd> at the
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<span class="sc">gdb</span> prompt to see a list of commands in this category.
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<br><dt><code>COMMAND_BREAKPOINTS</code><a name="index-COMMAND_005fBREAKPOINTS-2624"></a><dd>The command has to do with breakpoints. For example, <code>break</code>,
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<code>clear</code>, and <code>delete</code> are in this category. Type <kbd>help
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breakpoints</kbd> at the <span class="sc">gdb</span> prompt to see a list of commands in
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this category.
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<br><dt><code>COMMAND_TRACEPOINTS</code><a name="index-COMMAND_005fTRACEPOINTS-2625"></a><dd>The command has to do with tracepoints. For example, <code>trace</code>,
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<code>actions</code>, and <code>tfind</code> are in this category. Type
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<kbd>help tracepoints</kbd> at the <span class="sc">gdb</span> prompt to see a list of
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commands in this category.
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<br><dt><code>COMMAND_USER</code><a name="index-COMMAND_005fUSER-2626"></a><dd>The command is a general purpose command for the user, and typically
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does not fit in one of the other categories.
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Type <kbd>help user-defined</kbd> at the <span class="sc">gdb</span> prompt to see
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a list of commands in this category, as well as the list of gdb macros
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(see <a href="Sequences.html#Sequences">Sequences</a>).
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<br><dt><code>COMMAND_OBSCURE</code><a name="index-COMMAND_005fOBSCURE-2627"></a><dd>The command is only used in unusual circumstances, or is not of
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general interest to users. For example, <code>checkpoint</code>,
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<code>fork</code>, and <code>stop</code> are in this category. Type <kbd>help
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obscure</kbd> at the <span class="sc">gdb</span> prompt to see a list of commands in this
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category.
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<br><dt><code>COMMAND_MAINTENANCE</code><a name="index-COMMAND_005fMAINTENANCE-2628"></a><dd>The command is only useful to <span class="sc">gdb</span> maintainers. The
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<code>maintenance</code> and <code>flushregs</code> commands are in this category.
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Type <kbd>help internals</kbd> at the <span class="sc">gdb</span> prompt to see a list of
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commands in this category.
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</dl>
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<p>A new command can use a predefined completion function, either by
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specifying it via an argument at initialization, or by returning it
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from the <code>completer</code> procedure. These predefined completion
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constants are all defined in the <code>gdb</code> module:
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<dl>
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<dt><code>COMPLETE_NONE</code><a name="index-COMPLETE_005fNONE-2629"></a><dd>This constant means that no completion should be done.
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<br><dt><code>COMPLETE_FILENAME</code><a name="index-COMPLETE_005fFILENAME-2630"></a><dd>This constant means that filename completion should be performed.
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<br><dt><code>COMPLETE_LOCATION</code><a name="index-COMPLETE_005fLOCATION-2631"></a><dd>This constant means that location completion should be done.
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See <a href="Specify-Location.html#Specify-Location">Specify Location</a>.
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<br><dt><code>COMPLETE_COMMAND</code><a name="index-COMPLETE_005fCOMMAND-2632"></a><dd>This constant means that completion should examine <span class="sc">gdb</span>
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command names.
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<br><dt><code>COMPLETE_SYMBOL</code><a name="index-COMPLETE_005fSYMBOL-2633"></a><dd>This constant means that completion should be done using symbol names
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as the source.
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<br><dt><code>COMPLETE_EXPRESSION</code><a name="index-COMPLETE_005fEXPRESSION-2634"></a><dd>This constant means that completion should be done on expressions.
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Often this means completing on symbol names, but some language
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parsers also have support for completing on field names.
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</dl>
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<p>The following code snippet shows how a trivial CLI command can be
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implemented in Guile:
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<pre class="smallexample"> (gdb) guile
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(register-command! (make-command "hello-world"
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#:command-class COMMAND_USER
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#:doc "Greet the whole world."
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#:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
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end
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(gdb) hello-world
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Hello, World!
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</pre>
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</body></html>
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