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| <h4 class="subsection">23.1.2 User-defined Command Hooks</h4> |
| |
| <p><a name="index-command-hooks-1545"></a><a name="index-hooks_002c-for-commands-1546"></a><a name="index-hooks_002c-pre_002dcommand-1547"></a> |
| <a name="index-hook-1548"></a>You may define <dfn>hooks</dfn>, which are a special kind of user-defined |
| command. Whenever you run the command ‘<samp><span class="samp">foo</span></samp>’, if the user-defined |
| command ‘<samp><span class="samp">hook-foo</span></samp>’ exists, it is executed (with no arguments) |
| before that command. |
| |
| <p><a name="index-hooks_002c-post_002dcommand-1549"></a><a name="index-hookpost-1550"></a>A hook may also be defined which is run after the command you executed. |
| Whenever you run the command ‘<samp><span class="samp">foo</span></samp>’, if the user-defined command |
| ‘<samp><span class="samp">hookpost-foo</span></samp>’ exists, it is executed (with no arguments) after |
| that command. Post-execution hooks may exist simultaneously with |
| pre-execution hooks, for the same command. |
| |
| <p>It is valid for a hook to call the command which it hooks. If this |
| occurs, the hook is not re-executed, thereby avoiding infinite recursion. |
| |
| <!-- It would be nice if hookpost could be passed a parameter indicating --> |
| <!-- if the command it hooks executed properly or not. FIXME! --> |
| <p><a name="index-stop_0040r_007b_002c-a-pseudo_002dcommand_007d-1551"></a>In addition, a pseudo-command, ‘<samp><span class="samp">stop</span></samp>’ exists. Defining |
| (‘<samp><span class="samp">hook-stop</span></samp>’) makes the associated commands execute every time |
| execution stops in your program: before breakpoint commands are run, |
| displays are printed, or the stack frame is printed. |
| |
| <p>For example, to ignore <code>SIGALRM</code> signals while |
| single-stepping, but treat them normally during normal execution, |
| you could define: |
| |
| <pre class="smallexample"> define hook-stop |
| handle SIGALRM nopass |
| end |
| |
| define hook-run |
| handle SIGALRM pass |
| end |
| |
| define hook-continue |
| handle SIGALRM pass |
| end |
| </pre> |
| <p>As a further example, to hook at the beginning and end of the <code>echo</code> |
| command, and to add extra text to the beginning and end of the message, |
| you could define: |
| |
| <pre class="smallexample"> define hook-echo |
| echo <<<--- |
| end |
| |
| define hookpost-echo |
| echo --->>>\n |
| end |
| |
| (gdb) echo Hello World |
| <<<---Hello World--->>> |
| (gdb) |
| |
| </pre> |
| <p>You can define a hook for any single-word command in <span class="sc">gdb</span>, but |
| not for command aliases; you should define a hook for the basic command |
| name, e.g. <code>backtrace</code> rather than <code>bt</code>. |
| <!-- FIXME! So how does Joe User discover whether a command is an alias --> |
| <!-- or not? --> |
| You can hook a multi-word command by adding <code>hook-</code> or |
| <code>hookpost-</code> to the last word of the command, e.g. |
| ‘<samp><span class="samp">define target hook-remote</span></samp>’ to add a hook to ‘<samp><span class="samp">target remote</span></samp>’. |
| |
| <p>If an error occurs during the execution of your hook, execution of |
| <span class="sc">gdb</span> commands stops and <span class="sc">gdb</span> issues a prompt |
| (before the command that you actually typed had a chance to run). |
| |
| <p>If you try to define a hook which does not match any known command, you |
| get a warning from the <code>define</code> command. |
| |
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