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<h5 class="subsubsection">23.3.3.11 Commands In Guile</h5>

<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
command object is created with the <code>make-command</code> Guile function,
and added to <span class="sc">gdb</span> 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 <span class="sc">gdb</span> from <code>make-command</code>.

   <p>There is no support for multi-line commands, that is commands that
consist of multiple lines and are terminated with <code>end</code>.

<!-- TODO: line length -->
<div class="defun">
&mdash; 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>
<blockquote>
        <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>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 <span class="sc">gdb</span>
with <code>register-command!</code>.

        <p>The rest of the arguments are optional.

        <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 <span class="sc">gdb</span> <code>error</code> call. 
Otherwise, the return value is ignored.

        <p>The argument <var>command-class</var> is one of the &lsquo;<samp><span class="samp">COMMAND_</span></samp>&rsquo; constants
defined below.  This argument tells <span class="sc">gdb</span> how to categorize the
new command in the help system.  The default is <code>COMMAND_NONE</code>.

        <p>The argument <var>completer</var> is either <code>#f</code>, one of the &lsquo;<samp><span class="samp">COMPLETE_</span></samp>&rsquo;
constants defined below, or a procedure, also defined below. 
This argument tells <span class="sc">gdb</span> 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>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>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></blockquote></div>

<div class="defun">
&mdash; Scheme Procedure: <b>register-command!</b><var> command<a name="index-register_002dcommand_0021-2609"></a></var><br>
<blockquote><p>Add <var>command</var>, a <code>&lt;gdb:command&gt;</code> object, to <span class="sc">gdb</span>'s
list of commands. 
It is an error to register a command more than once. 
The result is unspecified. 
</p></blockquote></div>

<div class="defun">
&mdash; Scheme Procedure: <b>command?</b><var> object<a name="index-command_003f-2610"></a></var><br>
<blockquote><p>Return <code>#t</code> if <var>object</var> is a <code>&lt;gdb:command&gt;</code> object. 
Otherwise return <code>#f</code>. 
</p></blockquote></div>

   <p><a name="index-don_0027t-repeat-Guile-command-2611"></a>

<div class="defun">
&mdash; Scheme Procedure: <b>dont-repeat</b><var><a name="index-dont_002drepeat-2612"></a></var><br>
<blockquote><p>By default, a <span class="sc">gdb</span> 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></blockquote></div>

<div class="defun">
&mdash; Scheme Procedure: <b>string-&gt;argv</b><var> string<a name="index-string_002d_003eargv-2613"></a></var><br>
<blockquote><p>Convert a string to a list of strings split up according to
<span class="sc">gdb</span>'s argv parsing rules. 
It is recommended to use this for consistency. 
Arguments are separated by spaces and may be quoted. 
Example:

     <pre class="smallexample">          scheme@(guile-user)&gt; (string-&gt;argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"")
          $1 = ("1" "2 \"3" "4 \"5" "6 '7")
</pre>
        </blockquote></div>

<div class="defun">
&mdash; Scheme Procedure: <b>throw-user-error</b><var> message . args<a name="index-throw_002duser_002derror-2614"></a></var><br>
<blockquote><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="../guile/Formatted-Output.html#Formatted-Output">Formatted Output</a>. 
The argument <var>args</var> is a list of the optional arguments of <var>message</var>.

        <p>This is used when the command detects a user error of some kind,
say a bad command argument.

     <pre class="smallexample">          (gdb) guile (use-modules (gdb))
          (gdb) guile
          (register-command! (make-command "test-user-error"
            #:command-class COMMAND_OBSCURE
            #:invoke (lambda (self arg from-tty)
              (throw-user-error "Bad argument ~a" arg))))
          end
          (gdb) test-user-error ugh
          ERROR: Bad argument ugh
</pre>
        </blockquote></div>

   <p><a name="index-completion-of-Guile-commands-2615"></a>

<div class="defun">
&mdash; completer: <b>self</b><var> text word<a name="index-self-2616"></a></var><br>
<blockquote><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's
location.  The argument <var>word</var> holds the last word of the command line;
this is computed using a word-breaking heuristic.

        <p>All forms of completion are handled by this function, that is,
the &lt;TAB&gt; and &lt;M-?&gt; 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>This procedure can return several kinds of values:

          <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>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>All other results are treated as though there were no available
completions. 
</ul>
        </p></blockquote></div>

   <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:

     <dl>
<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
this category will not be displayed in any of the help categories. 
This is the default.

     <br><dt><code>COMMAND_RUNNING</code><a name="index-COMMAND_005fRUNNING-2618"></a><dd>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 <span class="sc">gdb</span> prompt to see a list of
commands in this category.

     <br><dt><code>COMMAND_DATA</code><a name="index-COMMAND_005fDATA-2619"></a><dd>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 <span class="sc">gdb</span> prompt to see a list of commands
in this category.

     <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,
<code>backtrace</code>, <code>frame</code>, and <code>return</code> are in this
category.  Type <kbd>help stack</kbd> at the <span class="sc">gdb</span> prompt to see a
list of commands in this category.

     <br><dt><code>COMMAND_FILES</code><a name="index-COMMAND_005fFILES-2621"></a><dd>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 <span class="sc">gdb</span> prompt to see a list of
commands in this category.

     <br><dt><code>COMMAND_SUPPORT</code><a name="index-COMMAND_005fSUPPORT-2622"></a><dd>This should be used for &ldquo;support facilities&rdquo;, generally meaning
things that are useful to the user when interacting with <span class="sc">gdb</span>,
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 <span class="sc">gdb</span> prompt to see a list of
commands in this category.

     <br><dt><code>COMMAND_STATUS</code><a name="index-COMMAND_005fSTATUS-2623"></a><dd>The command is an &lsquo;<samp><span class="samp">info</span></samp>&rsquo;-related command, that is, related to the
state of <span class="sc">gdb</span> itself.  For example, <code>info</code>, <code>macro</code>,
and <code>show</code> are in this category.  Type <kbd>help status</kbd> at the
<span class="sc">gdb</span> prompt to see a list of commands in this category.

     <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>,
<code>clear</code>, and <code>delete</code> are in this category.  Type <kbd>help
breakpoints</kbd> at the <span class="sc">gdb</span> prompt to see a list of commands in
this category.

     <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>,
<code>actions</code>, and <code>tfind</code> are in this category.  Type
<kbd>help tracepoints</kbd> at the <span class="sc">gdb</span> prompt to see a list of
commands in this category.

     <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
does not fit in one of the other categories. 
Type <kbd>help user-defined</kbd> at the <span class="sc">gdb</span> 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>).

     <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
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 <span class="sc">gdb</span> prompt to see a list of commands in this
category.

     <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
<code>maintenance</code> and <code>flushregs</code> commands are in this category. 
Type <kbd>help internals</kbd> at the <span class="sc">gdb</span> prompt to see a list of
commands in this category. 
</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:

     <dl>
<dt><code>COMPLETE_NONE</code><a name="index-COMPLETE_005fNONE-2629"></a><dd>This constant means that no completion should be done.

     <br><dt><code>COMPLETE_FILENAME</code><a name="index-COMPLETE_005fFILENAME-2630"></a><dd>This constant means that filename completion should be performed.

     <br><dt><code>COMPLETE_LOCATION</code><a name="index-COMPLETE_005fLOCATION-2631"></a><dd>This constant means that location completion should be done. 
See <a href="Specify-Location.html#Specify-Location">Specify Location</a>.

     <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>
command names.

     <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
as the source.

     <br><dt><code>COMPLETE_EXPRESSION</code><a name="index-COMPLETE_005fEXPRESSION-2634"></a><dd>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. 
</dl>

   <p>The following code snippet shows how a trivial CLI command can be
implemented in Guile:

<pre class="smallexample">     (gdb) guile
     (register-command! (make-command "hello-world"
       #:command-class COMMAND_USER
       #:doc "Greet the whole world."
       #:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
     end
     (gdb) hello-world
     Hello, World!
</pre>
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