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<title>Command History - Debugging with GDB</title>
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<h3 class="section">22.3 Command History</h3>
<p><a name="index-command-history-1660"></a>
<span class="sc">gdb</span> can keep track of the commands you type during your
debugging sessions, so that you can be certain of precisely what
happened. Use these commands to manage the <span class="sc">gdb</span> command
history facility.
<p><span class="sc">gdb</span> uses the <span class="sc">gnu</span> History library, a part of the Readline
package, to provide the history facility.
See <a href="Using-History-Interactively.html#Using-History-Interactively">Using History Interactively</a>,
for the detailed description of the History library.
<p>To issue a command to <span class="sc">gdb</span> without affecting certain aspects of
the state which is seen by users, prefix it with &lsquo;<samp><span class="samp">server </span></samp>&rsquo;
(see <a href="Server-Prefix.html#Server-Prefix">Server Prefix</a>). This
means that this command will not affect the command history, nor will it
affect <span class="sc">gdb</span>'s notion of which command to repeat if &lt;RET&gt; is
pressed on a line by itself.
<p><a name="index-g_t_0040code_007bserver_007d_002c-command-prefix-1661"></a>The server prefix does not affect the recording of values into the value
history; to print a value without recording it into the value history,
use the <code>output</code> command instead of the <code>print</code> command.
<p>Here is the description of <span class="sc">gdb</span> commands related to command
history.
<a name="index-history-substitution-1662"></a>
<a name="index-history-file-1663"></a>
<a name="index-set-history-filename-1664"></a>
<a name="index-g_t_0040env_007bGDBHISTFILE_007d_002c-environment-variable-1665"></a>
<dl><dt><code>set history filename </code><var>fname</var><dd>Set the name of the <span class="sc">gdb</span> command history file to <var>fname</var>.
This is the file where <span class="sc">gdb</span> reads an initial command history
list, and where it writes the command history from this session when it
exits. You can access this list through history expansion or through
the history command editing characters listed below. This file defaults
to the value of the environment variable <code>GDBHISTFILE</code>, or to
<samp><span class="file">./.gdb_history</span></samp> (<samp><span class="file">./_gdb_history</span></samp> on MS-DOS) if this variable
is not set.
<p><a name="index-save-command-history-1666"></a><a name="index-set-history-save-1667"></a><br><dt><code>set history save</code><dt><code>set history save on</code><dd>Record command history in a file, whose name may be specified with the
<code>set history filename</code> command. By default, this option is disabled.
<br><dt><code>set history save off</code><dd>Stop recording command history in a file.
<p><a name="index-history-size-1668"></a><a name="index-set-history-size-1669"></a><a name="index-g_t_0040env_007bGDBHISTSIZE_007d_002c-environment-variable-1670"></a><br><dt><code>set history size </code><var>size</var><dt><code>set history size unlimited</code><dd>Set the number of commands which <span class="sc">gdb</span> keeps in its history list.
This defaults to the value of the environment variable <samp><span class="env">GDBHISTSIZE</span></samp>, or
to 256 if this variable is not set. Non-numeric values of <samp><span class="env">GDBHISTSIZE</span></samp>
are ignored. If <var>size</var> is <code>unlimited</code> or if <samp><span class="env">GDBHISTSIZE</span></samp> is
either a negative number or the empty string, then the number of commands
<span class="sc">gdb</span> keeps in the history list is unlimited.
<p><a name="index-remove-duplicate-history-1671"></a><a name="index-set-history-remove_002dduplicates-1672"></a><br><dt><code>set history remove-duplicates </code><var>count</var><dt><code>set history remove-duplicates unlimited</code><dd>Control the removal of duplicate history entries in the command history list.
If <var>count</var> is non-zero, <span class="sc">gdb</span> will look back at the last <var>count</var>
history entries and remove the first entry that is a duplicate of the current
entry being added to the command history list. If <var>count</var> is
<code>unlimited</code> then this lookbehind is unbounded. If <var>count</var> is 0, then
removal of duplicate history entries is disabled.
<p>Only history entries added during the current session are considered for
removal. This option is set to 0 by default.
</dl>
<p>History expansion assigns special meaning to the character <kbd>!</kbd>.
See <a href="Event-Designators.html#Event-Designators">Event Designators</a>,
for more details.
<p><a name="index-history-expansion_002c-turn-on_002foff-1673"></a>Since <kbd>!</kbd> is also the logical not operator in C, history expansion
is off by default. If you decide to enable history expansion with the
<code>set history expansion on</code> command, you may sometimes need to
follow <kbd>!</kbd> (when it is used as logical not, in an expression) with
a space or a tab to prevent it from being expanded. The readline
history facilities do not attempt substitution on the strings
<kbd>!=</kbd> and <kbd>!(</kbd>, even when history expansion is enabled.
<p>The commands to control history expansion are:
<dl>
<dt><code>set history expansion on</code><dt><code>set history expansion</code><dd><a name="index-set-history-expansion-1674"></a>Enable history expansion. History expansion is off by default.
<br><dt><code>set history expansion off</code><dd>Disable history expansion.
<!-- @group -->
<p><a name="index-show-history-1675"></a><br><dt><code>show history</code><dt><code>show history filename</code><dt><code>show history save</code><dt><code>show history size</code><dt><code>show history expansion</code><dd>These commands display the state of the <span class="sc">gdb</span> history parameters.
<code>show history</code> by itself displays all four states.
<!-- @end group -->
</dl>
<a name="index-show-commands-1676"></a>
<a name="index-show-last-commands-1677"></a>
<a name="index-display-command-history-1678"></a>
<dl><dt><code>show commands</code><dd>Display the last ten commands in the command history.
<br><dt><code>show commands </code><var>n</var><dd>Print ten commands centered on command number <var>n</var>.
<br><dt><code>show commands +</code><dd>Print ten commands just after the commands last printed.
</dl>
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