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<title>Debugging with GDB: Commands In Guile</title>

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<a name="Commands-In-Guile"></a>
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<p>
Next: <a href="Parameters-In-Guile.html#Parameters-In-Guile" accesskey="n" rel="next">Parameters In Guile</a>, Previous: <a href="Writing-a-Guile-Pretty_002dPrinter.html#Writing-a-Guile-Pretty_002dPrinter" accesskey="p" rel="previous">Writing a Guile Pretty-Printer</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> &nbsp; [<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>
</div>
<hr>
<a name="Commands-In-Guile-1"></a>
<h4 class="subsubsection">23.3.3.11 Commands In Guile</h4>

<a name="index-commands-in-guile"></a>
<a name="index-guile-commands-1"></a>
<p>You can implement new <small>GDB</small> CLI commands in Guile.  A CLI
command object is created with the <code>make-command</code> Guile function,
and added to <small>GDB</small> with the <code>register-command!</code> Guile function.
This two-step approach is taken to separate out the side-effect of adding
the command to <small>GDB</small> from <code>make-command</code>.
</p>
<p>There is no support for multi-line commands, that is commands that
consist of multiple lines and are terminated with <code>end</code>.
</p>
<dl>
<dt><a name="index-_0028make_002dcommand"></a>Scheme Procedure: <strong>(make-command</strong> <em>name <span class="roman">[</span>#:invoke invoke] <span class="roman">[</span>#:command-class command-class<span class="roman">]</span> <span class="roman">[</span>#:completer-class completer] <span class="roman">[</span>#:prefix? prefix<span class="roman">]</span> <span class="roman">[</span>#:doc doc-string])</em></dt>
<dd>
<p>The argument <var>name</var> is the name of the command.  If <var>name</var> consists of
multiple words, then the initial words are looked for as prefix
commands.  In this case, if one of the prefix commands does not exist,
an exception is raised.
</p>
<p>The result is the <code>&lt;gdb:command&gt;</code> object representing the command.
The command is not usable until it has been registered with <small>GDB</small>
with <code>register-command!</code>.
</p>
<p>The rest of the arguments are optional.
</p>
<p>The argument <var>invoke</var> is a procedure of three arguments: <var>self</var>,
<var>args</var> and <var>from-tty</var>.  The argument <var>self</var> is the
<code>&lt;gdb:command&gt;</code> object representing the command.
The argument <var>args</var> is a string representing the arguments passed to
the command, after leading and trailing whitespace has been stripped.
The argument <var>from-tty</var> is a boolean flag and specifies whether the
command should consider itself to have been originated from the user
invoking it interactively.  If this function throws an exception,
it is turned into a <small>GDB</small> <code>error</code> call.
Otherwise, the return value is ignored.
</p>
<p>The argument <var>command-class</var> is one of the &lsquo;<samp>COMMAND_</samp>&rsquo; constants
defined below.  This argument tells <small>GDB</small> how to categorize the
new command in the help system.  The default is <code>COMMAND_NONE</code>.
</p>
<p>The argument <var>completer</var> is either <code>#f</code>, one of the &lsquo;<samp>COMPLETE_</samp>&rsquo;
constants defined below, or a procedure, also defined below.
This argument tells <small>GDB</small> how to perform completion
for this command.  If not provided or if the value is <code>#f</code>,
then no completion is performed on the command.
</p>
<p>The argument <var>prefix</var> is a boolean flag indicating whether the new
command is a prefix command; sub-commands of this command may be
registered.
</p>
<p>The argument <var>doc-string</var> is help text for the new command.
If no documentation string is provided, the default value &ldquo;This command is
not documented.&rdquo; is used.
</p></dd></dl>

<dl>
<dt><a name="index-register_002dcommand_0021"></a>Scheme Procedure: <strong>register-command!</strong> <em>command</em></dt>
<dd><p>Add <var>command</var>, a <code>&lt;gdb:command&gt;</code> object, to <small>GDB</small>&rsquo;s
list of commands.
It is an error to register a command more than once.
The result is unspecified.
</p></dd></dl>

<dl>
<dt><a name="index-command_003f"></a>Scheme Procedure: <strong>command?</strong> <em>object</em></dt>
<dd><p>Return <code>#t</code> if <var>object</var> is a <code>&lt;gdb:command&gt;</code> object.
Otherwise return <code>#f</code>.
</p></dd></dl>

<a name="index-don_0027t-repeat-Guile-command"></a>
<dl>
<dt><a name="index-dont_002drepeat"></a>Scheme Procedure: <strong>dont-repeat</strong></dt>
<dd><p>By default, a <small>GDB</small> command is repeated when the user enters a
blank line at the command prompt.  A command can suppress this
behavior by invoking the <code>dont-repeat</code> function.  This is similar
to the user command <code>dont-repeat</code>, see <a href="Define.html#Define">dont-repeat</a>.
</p></dd></dl>

<dl>
<dt><a name="index-string_002d_003eargv"></a>Scheme Procedure: <strong>string-&gt;argv</strong> <em>string</em></dt>
<dd><p>Convert a string to a list of strings split up according to
<small>GDB</small>&rsquo;s argv parsing rules.
It is recommended to use this for consistency.
Arguments are separated by spaces and may be quoted.
Example:
</p>
<div class="smallexample">
<pre class="smallexample">scheme@(guile-user)&gt; (string-&gt;argv &quot;1 2\\ \\\&quot;3 '4 \&quot;5' \&quot;6 '7\&quot;&quot;)
$1 = (&quot;1&quot; &quot;2 \&quot;3&quot; &quot;4 \&quot;5&quot; &quot;6 '7&quot;)
</pre></div>
</dd></dl>

<dl>
<dt><a name="index-throw_002duser_002derror"></a>Scheme Procedure: <strong>throw-user-error</strong> <em>message . args</em></dt>
<dd><p>Throw a <code>gdb:user-error</code> exception.
The argument <var>message</var> is the error message as a format string, like the 
<var>fmt</var> argument to the <code>format</code> Scheme function.
See <a href="http://www.gnu.org/software/guile/manual/html_node/Formatted-Output.html#Formatted-Output">Formatted Output</a> in <cite>GNU Guile Reference Manual</cite>.
The argument <var>args</var> is a list of the optional arguments of <var>message</var>.
</p>
<p>This is used when the command detects a user error of some kind,
say a bad command argument.
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) guile (use-modules (gdb))
(gdb) guile
(register-command! (make-command &quot;test-user-error&quot;
  #:command-class COMMAND_OBSCURE
  #:invoke (lambda (self arg from-tty)
    (throw-user-error &quot;Bad argument ~a&quot; arg))))
end
(gdb) test-user-error ugh
ERROR: Bad argument ugh
</pre></div>
</dd></dl>

<a name="index-completion-of-Guile-commands"></a>
<dl>
<dt><a name="index-self"></a>completer: <strong>self</strong> <em>text word</em></dt>
<dd><p>If the <var>completer</var> option to <code>make-command</code> is a procedure,
it takes three arguments: <var>self</var> which is the <code>&lt;gdb:command&gt;</code>
object, and <var>text</var> and <var>word</var> which are both strings.
The argument <var>text</var> holds the complete command line up to the cursor&rsquo;s
location.  The argument <var>word</var> holds the last word of the command line;
this is computed using a word-breaking heuristic.
</p>
<p>All forms of completion are handled by this function, that is,
the <tt class="key">TAB</tt> and <tt class="key">M-?</tt> key bindings (see <a href="Completion.html#Completion">Completion</a>),
and the <code>complete</code> command (see <a href="Help.html#Help">complete</a>).
</p>
<p>This procedure can return several kinds of values:
</p>
<ul>
<li> If the return value is a list, the contents of the list are used as the
completions.  It is up to <var>completer</var> to ensure that the
contents actually do complete the word.  An empty list is
allowed, it means that there were no completions available.  Only
string elements of the list are used; other elements in the
list are ignored.

</li><li> If the return value is a <code>&lt;gdb:iterator&gt;</code> object, it is iterated over to
obtain the completions.  It is up to <code>completer-procedure</code> to ensure
that the results actually do complete the word.  Only
string elements of the result are used; other elements in the
sequence are ignored.

</li><li> All other results are treated as though there were no available
completions.
</li></ul>
</dd></dl>

<p>When a new command is registered, it will have been declared as a member of
some general class of commands.  This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command.  The available classifications are represented by constants
defined in the <code>gdb</code> module:
</p>
<dl compact="compact">
<dt><code>COMMAND_NONE</code>
<a name="index-COMMAND_005fNONE-1"></a>
</dt>
<dd><p>The command does not belong to any particular class.  A command in
this category will not be displayed in any of the help categories.
This is the default.
</p>
</dd>
<dt><code>COMMAND_RUNNING</code>
<a name="index-COMMAND_005fRUNNING-1"></a>
</dt>
<dd><p>The command is related to running the inferior.  For example,
<code>start</code>, <code>step</code>, and <code>continue</code> are in this category.
Type <kbd>help running</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
</dd>
<dt><code>COMMAND_DATA</code>
<a name="index-COMMAND_005fDATA-1"></a>
</dt>
<dd><p>The command is related to data or variables.  For example,
<code>call</code>, <code>find</code>, and <code>print</code> are in this category.  Type
<kbd>help data</kbd> at the <small>GDB</small> prompt to see a list of commands
in this category.
</p>
</dd>
<dt><code>COMMAND_STACK</code>
<a name="index-COMMAND_005fSTACK-1"></a>
</dt>
<dd><p>The command has to do with manipulation of the stack.  For example,
<code>backtrace</code>, <code>frame</code>, and <code>return</code> are in this
category.  Type <kbd>help stack</kbd> at the <small>GDB</small> prompt to see a
list of commands in this category.
</p>
</dd>
<dt><code>COMMAND_FILES</code>
<a name="index-COMMAND_005fFILES-1"></a>
</dt>
<dd><p>This class is used for file-related commands.  For example,
<code>file</code>, <code>list</code> and <code>section</code> are in this category.
Type <kbd>help files</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
</dd>
<dt><code>COMMAND_SUPPORT</code>
<a name="index-COMMAND_005fSUPPORT-1"></a>
</dt>
<dd><p>This should be used for &ldquo;support facilities&rdquo;, generally meaning
things that are useful to the user when interacting with <small>GDB</small>,
but not related to the state of the inferior.  For example,
<code>help</code>, <code>make</code>, and <code>shell</code> are in this category.  Type
<kbd>help support</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
</dd>
<dt><code>COMMAND_STATUS</code>
<a name="index-COMMAND_005fSTATUS-1"></a>
</dt>
<dd><p>The command is an &lsquo;<samp>info</samp>&rsquo;-related command, that is, related to the
state of <small>GDB</small> itself.  For example, <code>info</code>, <code>macro</code>,
and <code>show</code> are in this category.  Type <kbd>help status</kbd> at the
<small>GDB</small> prompt to see a list of commands in this category.
</p>
</dd>
<dt><code>COMMAND_BREAKPOINTS</code>
<a name="index-COMMAND_005fBREAKPOINTS-1"></a>
</dt>
<dd><p>The command has to do with breakpoints.  For example, <code>break</code>,
<code>clear</code>, and <code>delete</code> are in this category.  Type <kbd>help
breakpoints</kbd> at the <small>GDB</small> prompt to see a list of commands in
this category.
</p>
</dd>
<dt><code>COMMAND_TRACEPOINTS</code>
<a name="index-COMMAND_005fTRACEPOINTS-1"></a>
</dt>
<dd><p>The command has to do with tracepoints.  For example, <code>trace</code>,
<code>actions</code>, and <code>tfind</code> are in this category.  Type
<kbd>help tracepoints</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p>
</dd>
<dt><code>COMMAND_USER</code>
<a name="index-COMMAND_005fUSER-1"></a>
</dt>
<dd><p>The command is a general purpose command for the user, and typically
does not fit in one of the other categories.
Type <kbd>help user-defined</kbd> at the <small>GDB</small> prompt to see
a list of commands in this category, as well as the list of gdb macros
(see <a href="Sequences.html#Sequences">Sequences</a>).
</p>
</dd>
<dt><code>COMMAND_OBSCURE</code>
<a name="index-COMMAND_005fOBSCURE-1"></a>
</dt>
<dd><p>The command is only used in unusual circumstances, or is not of
general interest to users.  For example, <code>checkpoint</code>,
<code>fork</code>, and <code>stop</code> are in this category.  Type <kbd>help
obscure</kbd> at the <small>GDB</small> prompt to see a list of commands in this
category.
</p>
</dd>
<dt><code>COMMAND_MAINTENANCE</code>
<a name="index-COMMAND_005fMAINTENANCE-1"></a>
</dt>
<dd><p>The command is only useful to <small>GDB</small> maintainers.  The
<code>maintenance</code> and <code>flushregs</code> commands are in this category.
Type <kbd>help internals</kbd> at the <small>GDB</small> prompt to see a list of
commands in this category.
</p></dd>
</dl>

<p>A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the <code>completer</code> procedure.  These predefined completion
constants are all defined in the <code>gdb</code> module:
</p>
<dl compact="compact">
<dt><code>COMPLETE_NONE</code>
<a name="index-COMPLETE_005fNONE-1"></a>
</dt>
<dd><p>This constant means that no completion should be done.
</p>
</dd>
<dt><code>COMPLETE_FILENAME</code>
<a name="index-COMPLETE_005fFILENAME-1"></a>
</dt>
<dd><p>This constant means that filename completion should be performed.
</p>
</dd>
<dt><code>COMPLETE_LOCATION</code>
<a name="index-COMPLETE_005fLOCATION-1"></a>
</dt>
<dd><p>This constant means that location completion should be done.
See <a href="Specify-Location.html#Specify-Location">Specify Location</a>.
</p>
</dd>
<dt><code>COMPLETE_COMMAND</code>
<a name="index-COMPLETE_005fCOMMAND-1"></a>
</dt>
<dd><p>This constant means that completion should examine <small>GDB</small>
command names.
</p>
</dd>
<dt><code>COMPLETE_SYMBOL</code>
<a name="index-COMPLETE_005fSYMBOL-1"></a>
</dt>
<dd><p>This constant means that completion should be done using symbol names
as the source.
</p>
</dd>
<dt><code>COMPLETE_EXPRESSION</code>
<a name="index-COMPLETE_005fEXPRESSION-1"></a>
</dt>
<dd><p>This constant means that completion should be done on expressions.
Often this means completing on symbol names, but some language
parsers also have support for completing on field names.
</p></dd>
</dl>

<p>The following code snippet shows how a trivial CLI command can be
implemented in Guile:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) guile
(register-command! (make-command &quot;hello-world&quot;
  #:command-class COMMAND_USER
  #:doc &quot;Greet the whole world.&quot;
  #:invoke (lambda (self args from-tty) (display &quot;Hello, World!\n&quot;))))
end
(gdb) hello-world
Hello, World!
</pre></div>

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