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<a name="Command-History"></a>
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<hr>
<a name="Command-History-1"></a>
<h3 class="section">22.3 Command History</h3>
<a name="index-command-history"></a>

<p><small>GDB</small> 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 <small>GDB</small> command
history facility.
</p>
<p><small>GDB</small> uses the <small>GNU</small> 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>
<p>To issue a command to <small>GDB</small> without affecting certain aspects of
the state which is seen by users, prefix it with &lsquo;<samp>server </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 <small>GDB</small>&rsquo;s notion of which command to repeat if <tt class="key">RET</tt> is
pressed on a line by itself.
</p>
<a name="index-server_002c-command-prefix"></a>
<p>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>
<p>Here is the description of <small>GDB</small> commands related to command
history.
</p>
<dl compact="compact">
<dd><a name="index-history-substitution"></a>
<a name="index-history-file"></a>
<a name="index-set-history-filename"></a>
<a name="index-GDBHISTFILE_002c-environment-variable"></a>
</dd>
<dt><code>set history filename <span class="roman">[</span><var>fname</var><span class="roman">]</span></code></dt>
<dd><p>Set the name of the <small>GDB</small> command history file to <var>fname</var>.
This is the file where <small>GDB</small> 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>./.gdb_history</samp> (<samp>./_gdb_history</samp> on MS-DOS) if this variable
is not set.
</p>
<p>The <code>GDBHISTFILE</code> environment variable is read after processing
any <small>GDB</small> initialization files (see <a href="Startup.html#Startup">Startup</a>) and after
processing any commands passed using command line options (for
example, <code>-ex</code>).
</p>
<p>If the <var>fname</var> argument is not given, or if the <code>GDBHISTFILE</code>
is the empty string then <small>GDB</small> will neither try to load an
existing history file, nor will it try to save the history on exit.
</p>
<a name="index-save-command-history"></a>
<a name="index-set-history-save"></a>
</dd>
<dt><code>set history save</code></dt>
<dt><code>set history save on</code></dt>
<dd><p>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.  The command history will be recorded when <small>GDB</small>
exits.  If <code>set history filename</code> is set to the empty string then
history saving is disabled, even when <code>set history save</code> is
<code>on</code>.
</p>
</dd>
<dt><code>set history save off</code></dt>
<dd><p>Don&rsquo;t record the command history into the file specified by <code>set
history filename</code> when <small>GDB</small> exits.
</p>
<a name="index-history-size"></a>
<a name="index-set-history-size"></a>
<a name="index-GDBHISTSIZE_002c-environment-variable"></a>
</dd>
<dt><code>set history size <var>size</var></code></dt>
<dt><code>set history size unlimited</code></dt>
<dd><p>Set the number of commands which <small>GDB</small> keeps in its history list.
This defaults to the value of the environment variable <code>GDBHISTSIZE</code>, or
to 256 if this variable is not set.  Non-numeric values of <code>GDBHISTSIZE</code>
are ignored.  If <var>size</var> is <code>unlimited</code> or if <code>GDBHISTSIZE</code> is
either a negative number or the empty string, then the number of commands
<small>GDB</small> keeps in the history list is unlimited.
</p>
<p>The <code>GDBHISTSIZE</code> environment variable is read after processing
any <small>GDB</small> initialization files (see <a href="Startup.html#Startup">Startup</a>) and after
processing any commands passed using command line options (for
example, <code>-ex</code>).
</p>
<a name="index-remove-duplicate-history"></a>
<a name="index-set-history-remove_002dduplicates"></a>
</dd>
<dt><code>set history remove-duplicates <var>count</var></code></dt>
<dt><code>set history remove-duplicates unlimited</code></dt>
<dd><p>Control the removal of duplicate history entries in the command history list.
If <var>count</var> is non-zero, <small>GDB</small> 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>
<p>Only history entries added during the current session are considered for
removal.  This option is set to 0 by default.
</p>
</dd>
</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"></a>
<p>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>
<p>The commands to control history expansion are:
</p>
<dl compact="compact">
<dt><code>set history expansion on</code></dt>
<dt><code>set history expansion</code></dt>
<dd><a name="index-set-history-expansion"></a>
<p>Enable history expansion.  History expansion is off by default.
</p>
</dd>
<dt><code>set history expansion off</code></dt>
<dd><p>Disable history expansion.
</p>
<a name="index-show-history"></a>
</dd>
<dt><code>show history</code></dt>
<dt><code>show history filename</code></dt>
<dt><code>show history save</code></dt>
<dt><code>show history size</code></dt>
<dt><code>show history expansion</code></dt>
<dd><p>These commands display the state of the <small>GDB</small> history parameters.
<code>show history</code> by itself displays all four states.
</p></dd>
</dl>

<dl compact="compact">
<dd><a name="index-show-commands"></a>
<a name="index-show-last-commands"></a>
<a name="index-display-command-history"></a>
</dd>
<dt><code>show commands</code></dt>
<dd><p>Display the last ten commands in the command history.
</p>
</dd>
<dt><code>show commands <var>n</var></code></dt>
<dd><p>Print ten commands centered on command number <var>n</var>.
</p>
</dd>
<dt><code>show commands +</code></dt>
<dd><p>Print ten commands just after the commands last printed.
</p></dd>
</dl>

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