160 lines
8.7 KiB
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160 lines
8.7 KiB
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<title>Command Files - Debugging with GDB</title>
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Permission is granted to copy, distribute and/or modify this document
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<body>
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<div class="node">
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<a name="Command-Files"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Output.html#Output">Output</a>,
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Previous: <a rel="previous" accesskey="p" href="Hooks.html#Hooks">Hooks</a>,
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Up: <a rel="up" accesskey="u" href="Sequences.html#Sequences">Sequences</a>
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<hr>
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</div>
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<h4 class="subsection">23.1.3 Command Files</h4>
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<p><a name="index-command-files-1817"></a><a name="index-scripting-commands-1818"></a>A command file for <span class="sc">gdb</span> is a text file made of lines that are
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<span class="sc">gdb</span> commands. Comments (lines starting with <kbd>#</kbd>) may
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also be included. An empty line in a command file does nothing; it
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does not mean to repeat the last command, as it would from the
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terminal.
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<p>You can request the execution of a command file with the <code>source</code>
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command. Note that the <code>source</code> command is also used to evaluate
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scripts that are not Command Files. The exact behavior can be configured
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using the <code>script-extension</code> setting.
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See <a href="Extending-GDB.html#Extending-GDB">Extending GDB</a>.
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<a name="index-source-1819"></a>
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<a name="index-execute-commands-from-a-file-1820"></a>
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<dl><dt><code>source [-s] [-v] </code><var>filename</var><dd>Execute the command file <var>filename</var>.
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</dl>
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<p>The lines in a command file are generally executed sequentially,
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unless the order of execution is changed by one of the
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<em>flow-control commands</em> described below. The commands are not
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printed as they are executed. An error in any command terminates
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execution of the command file and control is returned to the console.
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<p><span class="sc">gdb</span> first searches for <var>filename</var> in the current directory.
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If the file is not found there, and <var>filename</var> does not specify a
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directory, then <span class="sc">gdb</span> also looks for the file on the source search path
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(specified with the ‘<samp><span class="samp">directory</span></samp>’ command);
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except that <samp><span class="file">$cdir</span></samp> is not searched because the compilation directory
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is not relevant to scripts.
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<p>If <code>-s</code> is specified, then <span class="sc">gdb</span> searches for <var>filename</var>
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on the search path even if <var>filename</var> specifies a directory.
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The search is done by appending <var>filename</var> to each element of the
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search path. So, for example, if <var>filename</var> is <samp><span class="file">mylib/myscript</span></samp>
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and the search path contains <samp><span class="file">/home/user</span></samp> then <span class="sc">gdb</span> will
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look for the script <samp><span class="file">/home/user/mylib/myscript</span></samp>.
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The search is also done if <var>filename</var> is an absolute path.
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For example, if <var>filename</var> is <samp><span class="file">/tmp/myscript</span></samp> and
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the search path contains <samp><span class="file">/home/user</span></samp> then <span class="sc">gdb</span> will
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look for the script <samp><span class="file">/home/user/tmp/myscript</span></samp>.
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For DOS-like systems, if <var>filename</var> contains a drive specification,
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it is stripped before concatenation. For example, if <var>filename</var> is
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<samp><span class="file">d:myscript</span></samp> and the search path contains <samp><span class="file">c:/tmp</span></samp> then <span class="sc">gdb</span>
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will look for the script <samp><span class="file">c:/tmp/myscript</span></samp>.
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<p>If <code>-v</code>, for verbose mode, is given then <span class="sc">gdb</span> displays
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each command as it is executed. The option must be given before
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<var>filename</var>, and is interpreted as part of the filename anywhere else.
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<p>Commands that would ask for confirmation if used interactively proceed
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without asking when used in a command file. Many <span class="sc">gdb</span> commands that
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normally print messages to say what they are doing omit the messages
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when called from command files.
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<p><span class="sc">gdb</span> also accepts command input from standard input. In this
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mode, normal output goes to standard output and error output goes to
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standard error. Errors in a command file supplied on standard input do
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not terminate execution of the command file—execution continues with
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the next command.
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<pre class="smallexample"> gdb < cmds > log 2>&1
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</pre>
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<p>(The syntax above will vary depending on the shell used.) This example
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will execute commands from the file <samp><span class="file">cmds</span></samp>. All output and errors
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would be directed to <samp><span class="file">log</span></samp>.
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<p>Since commands stored on command files tend to be more general than
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commands typed interactively, they frequently need to deal with
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complicated situations, such as different or unexpected values of
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variables and symbols, changes in how the program being debugged is
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built, etc. <span class="sc">gdb</span> provides a set of flow-control commands to
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deal with these complexities. Using these commands, you can write
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complex scripts that loop over data structures, execute commands
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conditionally, etc.
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<a name="index-if-1821"></a>
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<a name="index-else-1822"></a>
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<dl><dt><code>if</code><dt><code>else</code><dd>This command allows to include in your script conditionally executed
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commands. The <code>if</code> command takes a single argument, which is an
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expression to evaluate. It is followed by a series of commands that
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are executed only if the expression is true (its value is nonzero).
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There can then optionally be an <code>else</code> line, followed by a series
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of commands that are only executed if the expression was false. The
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end of the list is marked by a line containing <code>end</code>.
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<p><a name="index-while-1823"></a><br><dt><code>while</code><dd>This command allows to write loops. Its syntax is similar to
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<code>if</code>: the command takes a single argument, which is an expression
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to evaluate, and must be followed by the commands to execute, one per
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line, terminated by an <code>end</code>. These commands are called the
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<dfn>body</dfn> of the loop. The commands in the body of <code>while</code> are
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executed repeatedly as long as the expression evaluates to true.
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<p><a name="index-loop_005fbreak-1824"></a><br><dt><code>loop_break</code><dd>This command exits the <code>while</code> loop in whose body it is included.
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Execution of the script continues after that <code>while</code>s <code>end</code>
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line.
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<p><a name="index-loop_005fcontinue-1825"></a><br><dt><code>loop_continue</code><dd>This command skips the execution of the rest of the body of commands
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in the <code>while</code> loop in whose body it is included. Execution
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branches to the beginning of the <code>while</code> loop, where it evaluates
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the controlling expression.
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<p><a name="index-end_0040r_007b-_0028if_002felse_002fwhile-commands_0029_007d-1826"></a><br><dt><code>end</code><dd>Terminate the block of commands that are the body of <code>if</code>,
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<code>else</code>, or <code>while</code> flow-control commands.
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</dl>
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</body></html>
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