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<title>Debugging with GDB: Define</title>
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<a name="Define"></a>
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<div class="header">
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<p>
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Next: <a href="Hooks.html#Hooks" accesskey="n" rel="next">Hooks</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</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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<hr>
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<a name="User_002ddefined-Commands"></a>
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<h4 class="subsection">23.1.1 User-defined Commands</h4>
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<a name="index-user_002ddefined-command"></a>
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<a name="index-arguments_002c-to-user_002ddefined-commands"></a>
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<p>A <em>user-defined command</em> is a sequence of <small>GDB</small> commands to
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which you assign a new name as a command. This is done with the
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<code>define</code> command. User commands may accept up to 10 arguments
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separated by whitespace. Arguments are accessed within the user command
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via <code>$arg0…$arg9</code>. A trivial example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">define adder
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print $arg0 + $arg1 + $arg2
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end
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</pre></div>
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<p>To execute the command use:
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</p>
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<div class="smallexample">
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<pre class="smallexample">adder 1 2 3
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</pre></div>
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<p>This defines the command <code>adder</code>, which prints the sum of
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its three arguments. Note the arguments are text substitutions, so they may
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reference variables, use complex expressions, or even perform inferior
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functions calls.
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</p>
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<a name="index-argument-count-in-user_002ddefined-commands"></a>
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<a name="index-how-many-arguments-_0028user_002ddefined-commands_0029"></a>
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<p>In addition, <code>$argc</code> may be used to find out how many arguments have
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been passed. This expands to a number in the range 0…10.
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</p>
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<div class="smallexample">
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<pre class="smallexample">define adder
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if $argc == 2
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print $arg0 + $arg1
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end
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if $argc == 3
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print $arg0 + $arg1 + $arg2
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end
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end
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</pre></div>
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<dl compact="compact">
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<dd>
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<a name="index-define"></a>
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</dd>
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<dt><code>define <var>commandname</var></code></dt>
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<dd><p>Define a command named <var>commandname</var>. If there is already a command
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by that name, you are asked to confirm that you want to redefine it.
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The argument <var>commandname</var> may be a bare command name consisting of letters,
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numbers, dashes, and underscores. It may also start with any predefined
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prefix command. For example, ‘<samp>define target my-target</samp>’ creates
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a user-defined ‘<samp>target my-target</samp>’ command.
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</p>
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<p>The definition of the command is made up of other <small>GDB</small> command lines,
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which are given following the <code>define</code> command. The end of these
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commands is marked by a line containing <code>end</code>.
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</p>
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<a name="index-document"></a>
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<a name="index-end-_0028user_002ddefined-commands_0029"></a>
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</dd>
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<dt><code>document <var>commandname</var></code></dt>
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<dd><p>Document the user-defined command <var>commandname</var>, so that it can be
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accessed by <code>help</code>. The command <var>commandname</var> must already be
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defined. This command reads lines of documentation just as <code>define</code>
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reads the lines of the command definition, ending with <code>end</code>.
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After the <code>document</code> command is finished, <code>help</code> on command
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<var>commandname</var> displays the documentation you have written.
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</p>
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<p>You may use the <code>document</code> command again to change the
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documentation of a command. Redefining the command with <code>define</code>
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does not change the documentation.
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</p>
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<a name="index-dont_002drepeat-1"></a>
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<a name="index-don_0027t-repeat-command"></a>
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</dd>
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<dt><code>dont-repeat</code></dt>
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<dd><p>Used inside a user-defined command, this tells <small>GDB</small> that this
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command should not be repeated when the user hits <tt class="key">RET</tt>
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(see <a href="Command-Syntax.html#Command-Syntax">repeat last command</a>).
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</p>
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<a name="index-help-user_002ddefined"></a>
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</dd>
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<dt><code>help user-defined</code></dt>
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<dd><p>List all user-defined commands and all python commands defined in class
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COMAND_USER. The first line of the documentation or docstring is
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included (if any).
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</p>
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<a name="index-show-user"></a>
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</dd>
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<dt><code>show user</code></dt>
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<dt><code>show user <var>commandname</var></code></dt>
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<dd><p>Display the <small>GDB</small> commands used to define <var>commandname</var> (but
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not its documentation). If no <var>commandname</var> is given, display the
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definitions for all user-defined commands.
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This does not work for user-defined python commands.
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</p>
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<a name="index-infinite-recursion-in-user_002ddefined-commands"></a>
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<a name="index-show-max_002duser_002dcall_002ddepth"></a>
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<a name="index-set-max_002duser_002dcall_002ddepth"></a>
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</dd>
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<dt><code>show max-user-call-depth</code></dt>
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<dt><code>set max-user-call-depth</code></dt>
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<dd><p>The value of <code>max-user-call-depth</code> controls how many recursion
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levels are allowed in user-defined commands before <small>GDB</small> suspects an
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infinite recursion and aborts the command.
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This does not apply to user-defined python commands.
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</p></dd>
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</dl>
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<p>In addition to the above commands, user-defined commands frequently
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use control flow commands, described in <a href="Command-Files.html#Command-Files">Command Files</a>.
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</p>
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<p>When user-defined commands are executed, the
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commands of the definition are not printed. An error in any command
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stops execution of the user-defined command.
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</p>
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<p>If used interactively, commands that would ask for confirmation proceed
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without asking when used inside a user-defined command. Many <small>GDB</small>
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commands that normally print messages to say what they are doing omit the
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messages when used in a user-defined command.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Hooks.html#Hooks" accesskey="n" rel="next">Hooks</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</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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