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| <title>Debugging with GDB: Commands In Python</title> |
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| <a name="Commands-In-Python"></a> |
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| Next: <a href="Parameters-In-Python.html#Parameters-In-Python" accesskey="n" rel="next">Parameters In Python</a>, Previous: <a href="Threads-In-Python.html#Threads-In-Python" accesskey="p" rel="prev">Threads In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</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> |
| <a name="Commands-In-Python-1"></a> |
| <h4 class="subsubsection">23.2.2.19 Commands In Python</h4> |
| |
| <a name="index-commands-in-python"></a> |
| <a name="index-python-commands-1"></a> |
| <p>You can implement new <small>GDB</small> CLI commands in Python. A CLI |
| command is implemented using an instance of the <code>gdb.Command</code> |
| class, most commonly using a subclass. |
| </p> |
| <dl> |
| <dt><a name="index-Command_002e_005f_005finit_005f_005f"></a>Function: <strong>Command.__init__</strong> <em>(name, <var>command_class</var> <span class="roman">[</span>, <var>completer_class</var> <span class="roman">[</span>, <var>prefix</var><span class="roman">]]</span>)</em></dt> |
| <dd><p>The object initializer for <code>Command</code> registers the new command |
| with <small>GDB</small>. This initializer is normally invoked from the |
| subclass’ own <code>__init__</code> method. |
| </p> |
| <p><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>There is no support for multi-line commands. |
| </p> |
| <p><var>command_class</var> should be one of the ‘<samp>COMMAND_</samp>’ constants |
| defined below. This argument tells <small>GDB</small> how to categorize the |
| new command in the help system. |
| </p> |
| <p><var>completer_class</var> is an optional argument. If given, it should be |
| one of the ‘<samp>COMPLETE_</samp>’ constants defined below. This argument |
| tells <small>GDB</small> how to perform completion for this command. If not |
| given, <small>GDB</small> will attempt to complete using the object’s |
| <code>complete</code> method (see below); if no such method is found, an |
| error will occur when completion is attempted. |
| </p> |
| <p><var>prefix</var> is an optional argument. If <code>True</code>, then the new |
| command is a prefix command; sub-commands of this command may be |
| registered. |
| </p> |
| <p>The help text for the new command is taken from the Python |
| documentation string for the command’s class, if there is one. If no |
| documentation string is provided, the default value “This command is |
| not documented.” is used. |
| </p></dd></dl> |
| |
| <a name="index-don_0027t-repeat-Python-command"></a> |
| <dl> |
| <dt><a name="index-Command_002edont_005frepeat"></a>Function: <strong>Command.dont_repeat</strong> <em>()</em></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> method. 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-Command_002einvoke"></a>Function: <strong>Command.invoke</strong> <em>(argument, from_tty)</em></dt> |
| <dd><p>This method is called by <small>GDB</small> when this command is invoked. |
| </p> |
| <p><var>argument</var> is a string. It is the argument to the command, after |
| leading and trailing whitespace has been stripped. |
| </p> |
| <p><var>from_tty</var> is a boolean argument. When true, this means that the |
| command was entered by the user at the terminal; when false it means |
| that the command came from elsewhere. |
| </p> |
| <p>If this method throws an exception, it is turned into a <small>GDB</small> |
| <code>error</code> call. Otherwise, the return value is ignored. |
| </p> |
| <a name="index-gdb_002estring_005fto_005fargv"></a> |
| <p>To break <var>argument</var> up into an argv-like string use |
| <code>gdb.string_to_argv</code>. This function behaves identically to |
| <small>GDB</small>’s internal argument lexer <code>buildargv</code>. |
| 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">print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"") |
| ['1', '2 "3', '4 "5', "6 '7"] |
| </pre></div> |
| |
| </dd></dl> |
| |
| <a name="index-completion-of-Python-commands"></a> |
| <dl> |
| <dt><a name="index-Command_002ecomplete"></a>Function: <strong>Command.complete</strong> <em>(text, word)</em></dt> |
| <dd><p>This method is called by <small>GDB</small> when the user attempts |
| completion on this command. All forms of completion are handled by |
| this method, 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>The arguments <var>text</var> and <var>word</var> are both strings; <var>text</var> |
| holds the complete command line up to the cursor’s location, while |
| <var>word</var> holds the last word of the command line; this is computed |
| using a word-breaking heuristic. |
| </p> |
| <p>The <code>complete</code> method can return several values: |
| </p><ul> |
| <li> If the return value is a sequence, the contents of the sequence are |
| used as the completions. It is up to <code>complete</code> to ensure that the |
| contents actually do complete the word. A zero-length sequence is |
| allowed, it means that there were no completions available. Only |
| string elements of the sequence are used; other elements in the |
| sequence are ignored. |
| |
| </li><li> If the return value is one of the ‘<samp>COMPLETE_</samp>’ constants defined |
| below, then the corresponding <small>GDB</small>-internal completion |
| function is invoked, and its result is used. |
| |
| </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 must be 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"> |
| <dd><a name="index-COMMAND_005fNONE"></a> |
| <a name="index-gdb_002eCOMMAND_005fNONE"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_NONE</code></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. |
| </p> |
| <a name="index-COMMAND_005fRUNNING"></a> |
| <a name="index-gdb_002eCOMMAND_005fRUNNING"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_RUNNING</code></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> |
| <a name="index-COMMAND_005fDATA"></a> |
| <a name="index-gdb_002eCOMMAND_005fDATA"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_DATA</code></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> |
| <a name="index-COMMAND_005fSTACK"></a> |
| <a name="index-gdb_002eCOMMAND_005fSTACK"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_STACK</code></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> |
| <a name="index-COMMAND_005fFILES"></a> |
| <a name="index-gdb_002eCOMMAND_005fFILES"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_FILES</code></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> |
| <a name="index-COMMAND_005fSUPPORT"></a> |
| <a name="index-gdb_002eCOMMAND_005fSUPPORT"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_SUPPORT</code></dt> |
| <dd><p>This should be used for “support facilities”, 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> |
| <a name="index-COMMAND_005fSTATUS"></a> |
| <a name="index-gdb_002eCOMMAND_005fSTATUS"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_STATUS</code></dt> |
| <dd><p>The command is an ‘<samp>info</samp>’-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> |
| <a name="index-COMMAND_005fBREAKPOINTS"></a> |
| <a name="index-gdb_002eCOMMAND_005fBREAKPOINTS"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_BREAKPOINTS</code></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> |
| <a name="index-COMMAND_005fTRACEPOINTS"></a> |
| <a name="index-gdb_002eCOMMAND_005fTRACEPOINTS"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_TRACEPOINTS</code></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> |
| <a name="index-COMMAND_005fUSER"></a> |
| <a name="index-gdb_002eCOMMAND_005fUSER"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_USER</code></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> |
| <a name="index-COMMAND_005fOBSCURE"></a> |
| <a name="index-gdb_002eCOMMAND_005fOBSCURE"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_OBSCURE</code></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> |
| <a name="index-COMMAND_005fMAINTENANCE"></a> |
| <a name="index-gdb_002eCOMMAND_005fMAINTENANCE"></a> |
| </dd> |
| <dt><code>gdb.COMMAND_MAINTENANCE</code></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>complete</code> method. These predefined completion |
| constants are all defined in the <code>gdb</code> module: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-COMPLETE_005fNONE"></a> |
| </dd> |
| <dt><code>gdb.COMPLETE_NONE</code> |
| <a name="index-gdb_002eCOMPLETE_005fNONE"></a> |
| </dt> |
| <dd><p>This constant means that no completion should be done. |
| </p> |
| <a name="index-COMPLETE_005fFILENAME"></a> |
| </dd> |
| <dt><code>gdb.COMPLETE_FILENAME</code> |
| <a name="index-gdb_002eCOMPLETE_005fFILENAME"></a> |
| </dt> |
| <dd><p>This constant means that filename completion should be performed. |
| </p> |
| <a name="index-COMPLETE_005fLOCATION"></a> |
| </dd> |
| <dt><code>gdb.COMPLETE_LOCATION</code> |
| <a name="index-gdb_002eCOMPLETE_005fLOCATION"></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> |
| <a name="index-COMPLETE_005fCOMMAND"></a> |
| </dd> |
| <dt><code>gdb.COMPLETE_COMMAND</code> |
| <a name="index-gdb_002eCOMPLETE_005fCOMMAND"></a> |
| </dt> |
| <dd><p>This constant means that completion should examine <small>GDB</small> |
| command names. |
| </p> |
| <a name="index-COMPLETE_005fSYMBOL"></a> |
| </dd> |
| <dt><code>gdb.COMPLETE_SYMBOL</code> |
| <a name="index-gdb_002eCOMPLETE_005fSYMBOL"></a> |
| </dt> |
| <dd><p>This constant means that completion should be done using symbol names |
| as the source. |
| </p> |
| <a name="index-COMPLETE_005fEXPRESSION"></a> |
| </dd> |
| <dt><code>gdb.COMPLETE_EXPRESSION</code> |
| <a name="index-gdb_002eCOMPLETE_005fEXPRESSION"></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 Python: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">class HelloWorld (gdb.Command): |
| """Greet the whole world.""" |
| |
| def __init__ (self): |
| super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER) |
| |
| def invoke (self, arg, from_tty): |
| print "Hello, World!" |
| |
| HelloWorld () |
| </pre></div> |
| |
| <p>The last line instantiates the class, and is necessary to trigger the |
| registration of the command with <small>GDB</small>. Depending on how the |
| Python code is read into <small>GDB</small>, you may need to import the |
| <code>gdb</code> module explicitly. |
| </p> |
| <hr> |
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