1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with the 8Invariant Sections being "Free Software" and "Free Software Needs 9Free Documentation", with the Front-Cover Texts being "A GNU Manual," 10and with the Back-Cover Texts as in (a) below. 11 12(a) The FSF's Back-Cover Text is: "You are free to copy and modify 13this GNU Manual. Buying copies from GNU Press supports the FSF in 14developing GNU and promoting software freedom." --> 15<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 16<head> 17<title>Debugging with GDB: Output</title> 18 19<meta name="description" content="Debugging with GDB: Output"> 20<meta name="keywords" content="Debugging with GDB: Output"> 21<meta name="resource-type" content="document"> 22<meta name="distribution" content="global"> 23<meta name="Generator" content="makeinfo"> 24<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 25<link href="index.html#Top" rel="start" title="Top"> 26<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> 27<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 28<link href="Sequences.html#Sequences" rel="up" title="Sequences"> 29<link href="Auto_002dloading-sequences.html#Auto_002dloading-sequences" rel="next" title="Auto-loading sequences"> 30<link href="Command-Files.html#Command-Files" rel="previous" title="Command Files"> 31<style type="text/css"> 32<!-- 33a.summary-letter {text-decoration: none} 34blockquote.smallquotation {font-size: smaller} 35div.display {margin-left: 3.2em} 36div.example {margin-left: 3.2em} 37div.indentedblock {margin-left: 3.2em} 38div.lisp {margin-left: 3.2em} 39div.smalldisplay {margin-left: 3.2em} 40div.smallexample {margin-left: 3.2em} 41div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 42div.smalllisp {margin-left: 3.2em} 43kbd {font-style:oblique} 44pre.display {font-family: inherit} 45pre.format {font-family: inherit} 46pre.menu-comment {font-family: serif} 47pre.menu-preformatted {font-family: serif} 48pre.smalldisplay {font-family: inherit; font-size: smaller} 49pre.smallexample {font-size: smaller} 50pre.smallformat {font-family: inherit; font-size: smaller} 51pre.smalllisp {font-size: smaller} 52span.nocodebreak {white-space:nowrap} 53span.nolinebreak {white-space:nowrap} 54span.roman {font-family:serif; font-weight:normal} 55span.sansserif {font-family:sans-serif; font-weight:normal} 56ul.no-bullet {list-style: none} 57--> 58</style> 59 60 61</head> 62 63<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 64<a name="Output"></a> 65<div class="header"> 66<p> 67Next: <a href="Auto_002dloading-sequences.html#Auto_002dloading-sequences" accesskey="n" rel="next">Auto-loading sequences</a>, Previous: <a href="Command-Files.html#Command-Files" accesskey="p" rel="previous">Command Files</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> 68</div> 69<hr> 70<a name="Commands-for-Controlled-Output"></a> 71<h4 class="subsection">23.1.4 Commands for Controlled Output</h4> 72 73<p>During the execution of a command file or a user-defined command, normal 74<small>GDB</small> output is suppressed; the only output that appears is what is 75explicitly printed by the commands in the definition. This section 76describes three commands useful for generating exactly the output you 77want. 78</p> 79<dl compact="compact"> 80<dd><a name="index-echo"></a> 81</dd> 82<dt><code>echo <var>text</var></code></dt> 83<dd><p>Print <var>text</var>. Nonprinting characters can be included in 84<var>text</var> using C escape sequences, such as ‘<samp>\n</samp>’ to print a 85newline. <strong>No newline is printed unless you specify one.</strong> 86In addition to the standard C escape sequences, a backslash followed 87by a space stands for a space. This is useful for displaying a 88string with spaces at the beginning or the end, since leading and 89trailing spaces are otherwise trimmed from all arguments. 90To print ‘<samp> <!-- /@w -->and foo = <!-- /@w --></samp>’, use the command 91‘<samp>echo \ <!-- /@w -->and foo = \ <!-- /@w --></samp>’. 92</p> 93<p>A backslash at the end of <var>text</var> can be used, as in C, to continue 94the command onto subsequent lines. For example, 95</p> 96<div class="smallexample"> 97<pre class="smallexample">echo This is some text\n\ 98which is continued\n\ 99onto several lines.\n 100</pre></div> 101 102<p>produces the same output as 103</p> 104<div class="smallexample"> 105<pre class="smallexample">echo This is some text\n 106echo which is continued\n 107echo onto several lines.\n 108</pre></div> 109 110<a name="index-output"></a> 111</dd> 112<dt><code>output <var>expression</var></code></dt> 113<dd><p>Print the value of <var>expression</var> and nothing but that value: no 114newlines, no ‘<samp>$<var>nn</var> = </samp>’. The value is not entered in the 115value history either. See <a href="Expressions.html#Expressions">Expressions</a>, for more information 116on expressions. 117</p> 118</dd> 119<dt><code>output/<var>fmt</var> <var>expression</var></code></dt> 120<dd><p>Print the value of <var>expression</var> in format <var>fmt</var>. You can use 121the same formats as for <code>print</code>. See <a href="Output-Formats.html#Output-Formats">Output 122Formats</a>, for more information. 123</p> 124<a name="index-printf"></a> 125</dd> 126<dt><code>printf <var>template</var>, <var>expressions</var>…</code></dt> 127<dd><p>Print the values of one or more <var>expressions</var> under the control of 128the string <var>template</var>. To print several values, make 129<var>expressions</var> be a comma-separated list of individual expressions, 130which may be either numbers or pointers. Their values are printed as 131specified by <var>template</var>, exactly as a C program would do by 132executing the code below: 133</p> 134<div class="smallexample"> 135<pre class="smallexample">printf (<var>template</var>, <var>expressions</var>…); 136</pre></div> 137 138<p>As in <code>C</code> <code>printf</code>, ordinary characters in <var>template</var> 139are printed verbatim, while <em>conversion specification</em> introduced 140by the ‘<samp>%</samp>’ character cause subsequent <var>expressions</var> to be 141evaluated, their values converted and formatted according to type and 142style information encoded in the conversion specifications, and then 143printed. 144</p> 145<p>For example, you can print two values in hex like this: 146</p> 147<div class="smallexample"> 148<pre class="smallexample">printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo 149</pre></div> 150 151<p><code>printf</code> supports all the standard <code>C</code> conversion 152specifications, including the flags and modifiers between the ‘<samp>%</samp>’ 153character and the conversion letter, with the following exceptions: 154</p> 155<ul> 156<li> The argument-ordering modifiers, such as ‘<samp>2$</samp>’, are not supported. 157 158</li><li> The modifier ‘<samp>*</samp>’ is not supported for specifying precision or 159width. 160 161</li><li> The ‘<samp>'</samp>’ flag (for separation of digits into groups according to 162<code>LC_NUMERIC'</code>) is not supported. 163 164</li><li> The type modifiers ‘<samp>hh</samp>’, ‘<samp>j</samp>’, ‘<samp>t</samp>’, and ‘<samp>z</samp>’ are not 165supported. 166 167</li><li> The conversion letter ‘<samp>n</samp>’ (as in ‘<samp>%n</samp>’) is not supported. 168 169</li><li> The conversion letters ‘<samp>a</samp>’ and ‘<samp>A</samp>’ are not supported. 170</li></ul> 171 172<p>Note that the ‘<samp>ll</samp>’ type modifier is supported only if the 173underlying <code>C</code> implementation used to build <small>GDB</small> supports 174the <code>long long int</code> type, and the ‘<samp>L</samp>’ type modifier is 175supported only if <code>long double</code> type is available. 176</p> 177<p>As in <code>C</code>, <code>printf</code> supports simple backslash-escape 178sequences, such as <code>\n</code>, ‘<samp>\t</samp>’, ‘<samp>\\</samp>’, ‘<samp>\"</samp>’, 179‘<samp>\a</samp>’, and ‘<samp>\f</samp>’, that consist of backslash followed by a 180single character. Octal and hexadecimal escape sequences are not 181supported. 182</p> 183<p>Additionally, <code>printf</code> supports conversion specifications for DFP 184(<em>Decimal Floating Point</em>) types using the following length modifiers 185together with a floating point specifier. 186letters: 187</p> 188<ul> 189<li> ‘<samp>H</samp>’ for printing <code>Decimal32</code> types. 190 191</li><li> ‘<samp>D</samp>’ for printing <code>Decimal64</code> types. 192 193</li><li> ‘<samp>DD</samp>’ for printing <code>Decimal128</code> types. 194</li></ul> 195 196<p>If the underlying <code>C</code> implementation used to build <small>GDB</small> has 197support for the three length modifiers for DFP types, other modifiers 198such as width and precision will also be available for <small>GDB</small> to use. 199</p> 200<p>In case there is no such <code>C</code> support, no additional modifiers will be 201available and the value will be printed in the standard way. 202</p> 203<p>Here’s an example of printing DFP types using the above conversion letters: 204</p><div class="smallexample"> 205<pre class="smallexample">printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl 206</pre></div> 207 208<a name="eval"></a><a name="index-eval"></a> 209</dd> 210<dt><code>eval <var>template</var>, <var>expressions</var>…</code></dt> 211<dd><p>Convert the values of one or more <var>expressions</var> under the control of 212the string <var>template</var> to a command line, and call it. 213</p> 214</dd> 215</dl> 216 217<hr> 218<div class="header"> 219<p> 220Next: <a href="Auto_002dloading-sequences.html#Auto_002dloading-sequences" accesskey="n" rel="next">Auto-loading sequences</a>, Previous: <a href="Command-Files.html#Command-Files" accesskey="p" rel="previous">Command Files</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> 221</div> 222 223 224 225</body> 226</html> 227