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| <h4 class="subsection">23.1.4 Commands for Controlled Output</h4> |
| |
| <p>During the execution of a command file or a user-defined command, normal |
| <span class="sc">gdb</span> output is suppressed; the only output that appears is what is |
| explicitly printed by the commands in the definition. This section |
| describes three commands useful for generating exactly the output you |
| want. |
| |
| |
| <a name="index-echo-1562"></a> |
| <dl><dt><code>echo </code><var>text</var><dd><!-- I do not consider backslash-space a standard C escape sequence --> |
| <!-- because it is not in ANSI. --> |
| Print <var>text</var>. Nonprinting characters can be included in |
| <var>text</var> using C escape sequences, such as ‘<samp><span class="samp">\n</span></samp>’ to print a |
| newline. <strong>No newline is printed unless you specify one.</strong> |
| In addition to the standard C escape sequences, a backslash followed |
| by a space stands for a space. This is useful for displaying a |
| string with spaces at the beginning or the end, since leading and |
| trailing spaces are otherwise trimmed from all arguments. |
| To print ‘<samp><span class="samp"> <!-- /@w -->and foo = <!-- /@w --></span></samp>’, use the command |
| ‘<samp><span class="samp">echo \ <!-- /@w -->and foo = \ <!-- /@w --></span></samp>’. |
| |
| <p>A backslash at the end of <var>text</var> can be used, as in C, to continue |
| the command onto subsequent lines. For example, |
| |
| <pre class="smallexample"> echo This is some text\n\ |
| which is continued\n\ |
| onto several lines.\n |
| </pre> |
| <p>produces the same output as |
| |
| <pre class="smallexample"> echo This is some text\n |
| echo which is continued\n |
| echo onto several lines.\n |
| </pre> |
| <p><a name="index-output-1563"></a><br><dt><code>output </code><var>expression</var><dd>Print the value of <var>expression</var> and nothing but that value: no |
| newlines, no ‘<samp><span class="samp">$</span><var>nn</var><span class="samp"> = </span></samp>’. The value is not entered in the |
| value history either. See <a href="Expressions.html#Expressions">Expressions</a>, for more information |
| on expressions. |
| |
| <br><dt><code>output/</code><var>fmt</var> <var>expression</var><dd>Print the value of <var>expression</var> in format <var>fmt</var>. You can use |
| the same formats as for <code>print</code>. See <a href="Output-Formats.html#Output-Formats">Output Formats</a>, for more information. |
| |
| <p><a name="index-printf-1564"></a><br><dt><code>printf </code><var>template</var><code>, </code><var>expressions</var><code>...</code><dd>Print the values of one or more <var>expressions</var> under the control of |
| the string <var>template</var>. To print several values, make |
| <var>expressions</var> be a comma-separated list of individual expressions, |
| which may be either numbers or pointers. Their values are printed as |
| specified by <var>template</var>, exactly as a C program would do by |
| executing the code below: |
| |
| <pre class="smallexample"> printf (<var>template</var>, <var>expressions</var>...); |
| </pre> |
| <p>As in <code>C</code> <code>printf</code>, ordinary characters in <var>template</var> |
| are printed verbatim, while <dfn>conversion specification</dfn> introduced |
| by the ‘<samp><span class="samp">%</span></samp>’ character cause subsequent <var>expressions</var> to be |
| evaluated, their values converted and formatted according to type and |
| style information encoded in the conversion specifications, and then |
| printed. |
| |
| <p>For example, you can print two values in hex like this: |
| |
| <pre class="smallexample"> printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo |
| </pre> |
| <p><code>printf</code> supports all the standard <code>C</code> conversion |
| specifications, including the flags and modifiers between the ‘<samp><span class="samp">%</span></samp>’ |
| character and the conversion letter, with the following exceptions: |
| |
| <ul> |
| <li>The argument-ordering modifiers, such as ‘<samp><span class="samp">2$</span></samp>’, are not supported. |
| |
| <li>The modifier ‘<samp><span class="samp">*</span></samp>’ is not supported for specifying precision or |
| width. |
| |
| <li>The ‘<samp><span class="samp">'</span></samp>’ flag (for separation of digits into groups according to |
| <code>LC_NUMERIC'</code>) is not supported. |
| |
| <li>The type modifiers ‘<samp><span class="samp">hh</span></samp>’, ‘<samp><span class="samp">j</span></samp>’, ‘<samp><span class="samp">t</span></samp>’, and ‘<samp><span class="samp">z</span></samp>’ are not |
| supported. |
| |
| <li>The conversion letter ‘<samp><span class="samp">n</span></samp>’ (as in ‘<samp><span class="samp">%n</span></samp>’) is not supported. |
| |
| <li>The conversion letters ‘<samp><span class="samp">a</span></samp>’ and ‘<samp><span class="samp">A</span></samp>’ are not supported. |
| </ul> |
| |
| <p class="noindent">Note that the ‘<samp><span class="samp">ll</span></samp>’ type modifier is supported only if the |
| underlying <code>C</code> implementation used to build <span class="sc">gdb</span> supports |
| the <code>long long int</code> type, and the ‘<samp><span class="samp">L</span></samp>’ type modifier is |
| supported only if <code>long double</code> type is available. |
| |
| <p>As in <code>C</code>, <code>printf</code> supports simple backslash-escape |
| sequences, such as <code>\n</code>, ‘<samp><span class="samp">\t</span></samp>’, ‘<samp><span class="samp">\\</span></samp>’, ‘<samp><span class="samp">\"</span></samp>’, |
| ‘<samp><span class="samp">\a</span></samp>’, and ‘<samp><span class="samp">\f</span></samp>’, that consist of backslash followed by a |
| single character. Octal and hexadecimal escape sequences are not |
| supported. |
| |
| <p>Additionally, <code>printf</code> supports conversion specifications for DFP |
| (<dfn>Decimal Floating Point</dfn>) types using the following length modifiers |
| together with a floating point specifier. |
| letters: |
| |
| <ul> |
| <li>‘<samp><span class="samp">H</span></samp>’ for printing <code>Decimal32</code> types. |
| |
| <li>‘<samp><span class="samp">D</span></samp>’ for printing <code>Decimal64</code> types. |
| |
| <li>‘<samp><span class="samp">DD</span></samp>’ for printing <code>Decimal128</code> types. |
| </ul> |
| |
| <p>If the underlying <code>C</code> implementation used to build <span class="sc">gdb</span> has |
| support for the three length modifiers for DFP types, other modifiers |
| such as width and precision will also be available for <span class="sc">gdb</span> to use. |
| |
| <p>In case there is no such <code>C</code> support, no additional modifiers will be |
| available and the value will be printed in the standard way. |
| |
| <p>Here's an example of printing DFP types using the above conversion letters: |
| <pre class="smallexample"> printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl |
| </pre> |
| <p><a name="index-eval-1565"></a><br><dt><code>eval </code><var>template</var><code>, </code><var>expressions</var><code>...</code><dd>Convert the values of one or more <var>expressions</var> under the control of |
| the string <var>template</var> to a command line, and call it. |
| |
| </dl> |
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