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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><link href=https://flokoe.github.io/bash-hackers-wiki/commands/builtin/printf/ rel=canonical><link href=../mapfile/ rel=prev><link href=../read/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.44"><title>The printf command - The Bash Hackers Wiki</title><link rel=stylesheet href=../../../assets/stylesheets/main.0253249f.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.06af60db.min.css><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link rel=stylesheet href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallback"><style>:root{--md-text-font:"Roboto";--md-code-font:"Roboto Mono"}</style><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#the-printf-command class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="The Bash Hackers Wiki" class="md-header__button md-logo" aria-label="The Bash Hackers Wiki" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> The Bash Hackers Wiki </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> The printf command </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(p
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</code></pre></div> <p>The text format is given in <code><FORMAT></code>, while all arguments the formatstring may point to are given after that, here, indicated by <code><ARGUMENTS...></code>.</p> <p>Thus, a typical <code>printf</code>-call looks like:</p> <div class=highlight><pre><span></span><code>printf "Surname: %s\nName: %s\n" "$SURNAME" "$FIRSTNAME"
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</code></pre></div> <p>where <code>"Surname: %s\nName: %s\n"</code> is the format specification, and the two variables are passed as arguments, the <code>%s</code> in the formatstring points to (for every format specifier you give, <code>printf</code> awaits one argument!).</p> <h3 id=options>Options<a class=headerlink href=#options title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Option</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>-v VAR</code></td> <td>If given, the output is assigned to the variable <code>VAR</code> instead of printed to <code>stdout</code> (comparable to <code>sprintf()</code> in some way)</td> </tr> </tbody> </table> <p>The <code>-v</code> Option can't assign directly to array indexes in Bash versions older than Bash 4.1.</p> <div class="admonition danger"> <p class=admonition-title>Danger</p> <p>In versions newer than 4.1, one must be careful when performing expansions into the first non-option argument of printf as this opens up the possibility of an easy code injection vulnerability.</p> <div class=highlight><pre><span></span><code>$ var='-vx[$(echo hi >&2)]'; printf "$var" hi; declare -p x
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hi
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declare -a x='([0]="hi")'
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</code></pre></div> <p>...where the echo can of course be replaced with any arbitrary command. If you must, either specify a hard-coded format string or use -- to signal the end of options. The exact same issue also applies to <a href=../read/ >read</a>, and a similar one to <a href=../mapfile/ >mapfile</a>, though performing expansions into their arguments is less common.</p> </div> <h3 id=arguments>Arguments<a class=headerlink href=#arguments title="Permanent link">¶</a></h3> <p>Of course in shell-meaning the arguments are just strings, however, the common C-notations plus some additions for number-constants are recognized to give a number-argument to <code>printf</code>:</p> <table> <thead> <tr> <th>Number-Format</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>N</code></td> <td>A normal decimal number</td> </tr> <tr> <td><code>0N</code></td> <td>An octal number</td> </tr> <tr> <td><code>0xN</code></td> <td>A hexadecimal number</td> </tr> <tr> <td><code>0XN</code></td> <td>A hexadecimal number</td> </tr> <tr> <td><code>"X</code></td> <td>(a literal double-quote infront of a character): interpreted as number (underlying codeset) <strong>don't forget escaping</strong></td> </tr> <tr> <td><code>'X</code></td> <td>(a literal single-quote infront of a character): interpreted as number (underlying codeset) <strong>don't forget escaping</strong></td> </tr> </tbody> </table> <p><u><strong>If more arguments than format specifiers</strong></u> are present, then the format string is re-used until the last argument is interpreted. If fewer format specifiers than arguments are present, then number-formats are set to zero, while string-formats are set to null (empty).</p> <p>Take care to avoid <a href=../../../syntax/expansion/wordsplit/ >word splitting</a>, as accidentally passing the wrong number of arguments can produce wildly different and unexpected results. See <a href=../../../syntax/words/ >this article</a>.</p> <div class="admonition danger"> <p class=admonition-title>Attention</p> <p>When a numerical format expects a number, the internal <code>printf</code>-command will use the common Bash arithmetic rules regarding the base. A command like the following example <strong>will</strong> throw an error, since <code>08</code> is not a valid octal number (<code>00</code> to <code>07</code>!):</p> <div class=highlight><pre><span></span><code>printf '%d\n' 08
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</code></pre></div> </div> <h3 id=format-strings>Format strings<a class=headerlink href=#format-strings title="Permanent link">¶</a></h3> <p>The format string interpretion is derived from the C <code>printf()</code> function family. Only format specifiers that end in one of the letters <code>diouxXfeEgGaAcs</code> are recognized.</p> <p>To print a literal <code>%</code> (percent-sign), use <code>%%</code> in the format string.</p> <p><u><strong>Again:</strong></u> Every format specifier expects an associated argument provided!</p> <p>These specifiers have different names, depending who you ask. But they all mean the same: A placeholder for data with a specified format:</p> <ul> <li>format placeholder</li> <li>conversion specification</li> <li>formatting token</li> <li>...</li> </ul> <table> <thead> <tr> <th>Format</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>%b</code></td> <td>Print the associated argument while interpreting backslash escapes in there</td> </tr> <tr> <td><code>%q</code></td> <td>Print the associated argument <strong>shell-quoted</strong>, reusable as input</td> </tr> <tr> <td><code>%d</code></td> <td>Print the associated argument as <strong>signed decimal</strong> number</td> </tr> <tr> <td><code>%i</code></td> <td>Same as <code>%d</code></td> </tr> <tr> <td><code>%o</code></td> <td>Print the associated argument as <strong>unsigned octal</strong> number</td> </tr> <tr> <td><code>%u</code></td> <td>Print the associated argument as <strong>unsigned decimal</strong> number</td> </tr> <tr> <td><code>%x</code></td> <td>Print the associated argument as <strong>unsigned hexadecimal</strong> number with lower-case hex-digits (a-f)</td> </tr> <tr> <td><code>%X</code></td> <td>Same as <code>%x</code>, but with upper-case hex-digits (A-F)</td> </tr> <tr> <td><code>%f</code></td> <td>Interpret and print the associated argument as <strong>floating point</strong> number</td> </tr> <tr> <td><code>%e</code></td> <td>Interpret the associated argument as <strong>double</strong>, and print it in <code><N>±e<N></code> format</td> </tr> <tr> <td><code>%E</code></td> <td>Same as <code>%e</code>, but with an upper-case <code>E</code> in the printed format</td> </tr> <tr> <td><code>%g</code></td> <td>Interprets the associated argument as <strong>double</strong>, but prints it like <code>%f</code> or <code>%e</code></td> </tr> <tr> <td><code>%G</code></td> <td>Same as <code>%g</code>, but print it like <code>%E</code></td> </tr> <tr> <td><code>%c</code></td> <td>Interprets the associated argument as <strong>char</strong>: only the first character of a given argument is printed</td> </tr> <tr> <td><code>%s</code></td> <td>Interprets the associated argument literally as string</td> </tr> <tr> <td><code>%n</code></td> <td>Assigns the number of characters printed so far to the variable named in the corresponding argument. Can't specify an array index. If the given name is already an array, the value is assigned to the zeroth element.</td> </tr> <tr> <td><code>%a</code></td> <td>Interprets the associated argument as <strong>double</strong>, and prints it in the form of a C99 <a href=http://www.exploringbinary.com/hexadecimal-floating-point-constants/ >hexadecimal floating-point literal</a>.</td> </tr> <tr> <td><code>%A</code></td> <td>Same as <code>%a</code>, but print it like <code>%E</code></td> </tr> <tr> <td><code>%(FORMAT)T</code></td> <td>output the date-time string resulting from using <code>FORMAT</code> as a format string for <code>strftime(3)</code>. The associated argument is the number of seconds since Epoch, or <code>-1</code> (current time) or <code>-2</code> (shell startup time). If no corresponding argument is supplies, the current time is used as default</td> </tr> <tr> <td><code>%%</code></td> <td>No conversion is done. Produces a <code>%</code> (percent sign)</td> </tr> </tbody> </table> <p>Some of the mentioned format specifiers can modify their behaviour by getting a format modifier:</p> <h3 id=modifiers>Modifiers<a class=headerlink href=#modifiers title="Permanent link">&par
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</code></pre></div> <h4 id=field-and-printing-modifiers>Field and printing modifiers<a class=headerlink href=#field-and-printing-modifiers title="Permanent link">¶</a></h4> <table> <thead> <tr> <th>Field</th> <th>output format</th> </tr> </thead> <tbody> <tr> <td><code><N></code></td> <td><strong>Any number</strong>: Specifies a <strong>minimum field width</strong>, if the text to print is shorter, it's padded with spaces, if the text is longer, the field is expanded</td> </tr> <tr> <td><code>.</code></td> <td><strong>The dot</strong>: Together with a field width, the field is <strong>not</strong> expanded when the text is longer, the text is truncated instead. "<code>%.s</code>" is an undocumented equivalent for "<code>%.0s</code>", which will force a field width of zero, effectively hiding the field from output</td> </tr> <tr> <td><code>*</code></td> <td><strong>The asterisk</strong>: the width is given as argument before the string or number. Usage (the "<code>*</code>" corresponds to the "<code>20</code>"): <code>printf "%*s\n" 20 "test string"</code></td> </tr> <tr> <td><code>#</code></td> <td>"Alternative format" for numbers: see table below</td> </tr> <tr> <td><code>-</code></td> <td><strong>Left-bound</strong> text printing in the field (standard is <strong>right-bound</strong>)</td> </tr> <tr> <td><code>0</code></td> <td>Pads numbers with zeros, not spaces</td> </tr> <tr> <td><code><space></code></td> <td>Pad a positive number with a space, where a minus (<code>-</code>) is for negative numbers</td> </tr> <tr> <td><code>+</code></td> <td>Prints all numbers <strong>signed</strong> (<code>+</code> for positive, <code>-</code> for negative)</td> </tr> <tr> <td><code>'</code></td> <td>For decimal conversions, the thousands grouping separator is applied to the integer portion of the output according to the current LC_NUMERIC</td> </tr> </tbody> </table> <p><u><strong>The "alternative format" modifier <code>#</code>:</strong></u></p> <table> <thead> <tr> <th>Alternative</th> <th>Format</th> </tr> </thead> <tbody> <tr> <td><code>%#o</code></td> <td>The octal number is printed with a leading zero, unless it's zero itself</td> </tr> <tr> <td><code>%#x</code>, <code>%#X</code></td> <td>The hex number is printed with a leading "<code>0x</code>"/"<code>0X</code>", unless it's zero</td> </tr> <tr> <td><code>%#g</code>, <code>%#G</code></td> <td>The float number is printed with <strong>trailing zeros</strong> until the number of digits for the current precision is reached (usually trailing zeros are not printed)</td> </tr> <tr> <td>all number formats except <code>%d</code>, <code>%o</code>, <code>%x</code>, <code>%X</code></td> <td>Always print a decimal point in the output, even if no digits follow it</td> </tr> </tbody> </table> <h4 id=precision>Precision<a class=headerlink href=#precision title="Permanent link">¶</a></h4> <p>The precision for a floating- or double-number can be specified by using <code>.<DIGITS></code>, where <code><DIGITS></code> is the number of digits for precision. If <code><DIGITS></code> is an asterisk (<code>*</code>), the precision is read from the argument that precedes the number to print, like (prints 4,3000000000):</p> <div class=highlight><pre><span></span><code>printf "%.*f\n" 10 4,3
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</code></pre></div> <p>The format <code>.*N</code> to specify the N'th argument for precision does not work in Bash.</p> <p>For strings, the precision specifies the maximum number of characters to print (i.e., the maximum field width). For integers, it specifies the number of digits to print (zero-padding!).</p> <h3 id=escape-codes>Escape codes<a class=headerlink href=#escape-codes title="Permanent link">¶</a></h3> <p>These are interpreted if used anywhere in the format string, or in an argument corresponding to a <code>%b</code> format.</p> <table> <thead> <tr> <th>Code</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>\\</code></td> <td>Prints the character <code>\</code> (backslash)</td> </tr> <tr> <td><code>\a</code></td> <td>Prints the alert character (ASCII code 7 decimal)</td> </tr> <tr> <td><code>\b</code></td> <td>Prints a backspace</td> </tr> <tr> <td><code>\f</code></td> <td>Prints a form-feed</td> </tr> <tr> <td><code>\n</code></td> <td>Prints a newline</td> </tr> <tr> <td><code>\r</code></td> <td>Prints a carriage-return</td> </tr> <tr> <td><code>\t</code></td> <td>Prints a horizontal tabulator</td> </tr> <tr> <td><code>\v</code></td> <td>Prints a vertical tabulator</td> </tr> <tr> <td><code>\"</code></td> <td>Prints a <code>'</code></td> </tr> <tr> <td><code>\?</code></td> <td>Prints a <code>?</code></td> </tr> <tr> <td><code><NNN></code></td> <td>Interprets <code><NNN></code> as <strong>octal</strong> number and prints the corresponding character from the character set</td> </tr> <tr> <td><code>\0<NNN></code></td> <td>same as <code><NNN></code></td> </tr> <tr> <td><code>\x<NNN></code></td> <td>Interprets <code><NNN></code> as <strong>hexadecimal</strong> number and prints the corresponding character from the character set (<strong>3 digits</strong>)</td> </tr> <tr> <td><code>\u<NNNN></code></td> <td>same as <code>\x<NNN></code>, but <strong>4 digits</strong></td> </tr> <tr> <td><code>\U<NNNNNNNN></code></td> <td>same as <code>\x<NNN></code>, but <strong>8 digits</strong></td> </tr> </tbody> </table> <p>The following additional escape and extra rules apply only to arguments associated with a <code>%b</code> format:</p> <table> <thead> <tr> <th>Escape Rule</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>\c</code></td> <td>Terminate output similarly to the <code>\c</code> escape used by <code>echo -e</code>. printf produces no additional output after coming across a <code>\c</code> escape in a <code>%b</code> argument.</td> </tr> </tbody> </table> <ul> <li>Backslashes in the escapes: <code>\'</code>, <code>\"</code>, and <code>\?</code> are not removed.</li> <li>Octal escapes beginning with <code>\0</code> may contain up to four digits. (POSIX specifies up to three).</li> </ul> <p>These are also respects in which <code>%b</code> differs from the escapes used by <a href=../../../syntax/quoting/#ansi_c_like_strings>\$\'...\'</a> style quoting.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <h3 id=snipplets>Snipplets<a class=headerlink href=#snipplets title="Permanent link">¶</a></h3> <ul> <li>print the decimal representation of a hexadecimal number (preserve the sign)<ul> <li><code>printf "%d\n" 0x41</code></li> <li><code>printf "%d\n" -0x41</code></li> <li><code>printf "%+d\n" 0x41</code></li> </ul> </li> <li>print the octal representation of a decimal number<ul> <li><code>printf "%o\n" 65</code></li> <li><code>printf "%05o\n" 65</code> (5 characters width, padded with zeros)</li> </ul> </li> <li>this prints a 0, since no argument is specified<ul> <li><code>printf "%d\n"</code></li> </ul> </li> <li>print the code number of the character <code>A</code><ul> <li><code>printf "%d\n" \'A</code></li> <li><code>printf "%d\n" "'A"</code></li> </ul> </li> <li>Generate a greeting banner and assign it to the variable <code>GREETER</code><ul> <li><code>printf -v GREETER "Hello %s" "$LOGNAME"</code></li> </ul> </li> <li>Print a text at the end of the line, using <code>t
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<a id=__codelineno-0-2 name=__codelineno-0-2 href=#__codelineno-0-2></a><span class=w> </span><span class=nb>printf</span><span class=w> </span><span class=s1>'%3d | %04o | 0x%02x\n'</span><span class=w> </span><span class=s2>"</span><span class=nv>$x</span><span class=s2>"</span><span class=w> </span><span class=s2>"</span><span class=nv>$x</span><span class=s2>"</span><span class=w> </span><span class=s2>"</span><span class=nv>$x</span><span class=s2>"</span>
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<a id=__codelineno-0-3 name=__codelineno-0-3 href=#__codelineno-0-3></a><span class=k>done</span>
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</code></pre></div> <h3 id=ensure-well-formatted-mac-address>Ensure well-formatted MAC address<a class=headerlink href=#ensure-well-formatted-mac-address title="Permanent link">¶</a></h3> <p>This code here will take a common MAC address and rewrite it into a well-known format (regarding leading zeros or upper/lowercase of the hex digits, ...):</p> <div class=highlight><pre><span></span><code>the_mac="0:13:ce:7:7a:ad"
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# lowercase hex digits
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the_mac="$(printf "%02x:%02x:%02x:%02x:%02x:%02x" 0x${the_mac//:/ 0x})"
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# or the uppercase-digits variant
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the_mac="$(printf "%02X:%02X:%02X:%02X:%02X:%02X" 0x${the_mac//:/ 0x})"
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</code></pre></div> <h3 id=replacement-echo>Replacement echo<a class=headerlink href=#replacement-echo title="Permanent link">¶</a></h3> <p>This code was found in Solaris manpage for echo(1).</p> <p>Solaris version of <code>/usr/bin/echo</code> is equivalent to:</p> <div class=highlight><pre><span></span><code>printf "%b\n" "$*"
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</code></pre></div> <p>Solaris <code>/usr/ucb/echo</code> is equivalent to:</p> <div class=highlight><pre><span></span><code>if [ "X$1" = "X-n" ]
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then
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shift
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printf "%s" "$*"
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else
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printf "%s\n" "$*"
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fi
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</code></pre></div> <h3 id=prargs-implementation>prargs Implementation<a class=headerlink href=#prargs-implementation title="Permanent link">¶</a></h3> <p>Working off the replacement echo, here is a terse implementation of prargs:</p> <div class=highlight><pre><span></span><code>printf '"%b"\n' "$0" "$@" | nl -v0 -s": "
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</code></pre></div> <h3 id=repeating-a-character-for-example-to-print-a-line>repeating a character (for example to print a line)<a class=headerlink href=#repeating-a-character-for-example-to-print-a-line title="Permanent link">¶</a></h3> <p>A small trick: Combining printf and parameter expansion to draw a line</p> <div class=highlight><pre><span></span><code>length=40
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printf -v line '%*s' "$length"
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echo ${line// /-}
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</code></pre></div> <p>or:</p> <div class=highlight><pre><span></span><code>length=40
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eval printf -v line '%.0s-' {1..$length}
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</code></pre></div> <h3 id=replacement-for-some-calls-to-date1>Replacement for some calls to date(1)<a class=headerlink href=#replacement-for-some-calls-to-date1 title="Permanent link">¶</a></h3> <p>The <code>%(...)T</code> format string is a direct interface to <code>strftime(3)</code>.</p> <div class=highlight><pre><span></span><code>$ printf 'This is week %(%U/%Y)T.\n' -1
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This is week 52/2010.
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</code></pre></div> <p>Please read the manpage of <code>strftime(3)</code> to get more information about the supported formats.</p> <h2 id=differences-from-awk-printf>differences from awk printf<a class=headerlink href=#differences-from-awk-printf title="Permanent link">¶</a></h2> <p>Awk also derives its <em>printf()</em> function from C, and therefore has similar format specifiers. However, in all versions of awk the space character is used as a string concatenation operator, so it cannot be used as an argument separator. <strong>Arguments to awk printf must be separated by commas.</strong> Some versions of awk do not require printf arguments to be surrounded by parentheses, but you should use them anyway to provide portability.</p> <p>In the following example, the two strings are concatenated by the intervening space so that no argument remains to fill the format.</p> <div class=highlight><pre><span></span><code>$ echo "Foo" | awk '{ printf "%s\n" $1 }'
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awk: (FILENAME=- FNR=1) fatal: not enough arguments to satisfy format string
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`%s
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Foo'
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^ ran out for this one
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</code></pre></div> <p>Simply replacing the space with a comma and adding parentheses yields correct awk syntax.</p> <div class=highlight><pre><span></span><code>$ echo "Foo" | awk '{ printf( "%s\n", $1 ) }'
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Foo
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</code></pre></div> <p>With appropriate metacharacter escaping the bash printf can be called from inside awk (as from perl and other languages that support shell callout) as long as you don't care about program efficiency or readability.</p> <div class=highlight><pre><span></span><code>echo "Foo" | awk '{ system( "printf \"%s\\n \" \"" $1 "\"" ) }'
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Foo
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</code></pre></div> <h2 id=differences-from-c-and-portability-considerations>Differences from C, and portability considerations<a class=headerlink href=#differences-from-c-and-portability-considerations title="Permanent link">¶</a></h2> <ul> <li> <p>The a, A, e, E, f, F, g, and G conversions are supported by Bash, but not required by POSIX.</p> </li> <li> <p>There is no wide-character support (wprintf). For instance, if you use <code>%c</code>, you're actually asking for the first byte of the argument. Likewise, the maximum field width modifier (dot) in combination with <code>%s</code> goes by bytes, not characters. This limits some of printf's functionality to working with ascii only. ksh93's <code>printf</code> supports the <code>L</code> modifier with <code>%s</code> and <code>%c</code> (but so far not <code>%S</code> or <code>%C</code>) in order to treat precision as character width, not byte count. zsh appears to adjust itself dynamically based upon <code>LANG</code> and <code>LC_CTYPE</code>. If <code>LC_CTYPE=C</code>, zsh will throw "character not in range" errors, and otherwise supports wide characters automatically if a variable-width encoding is set for the current locale.</p> </li> <li> <p>Bash recognizes and skips over any characters present in the length modifiers specified by POSIX during format string parsing.</p> </li> </ul> <p><div class=highlight><span class=filename>builtins/printf.def</span><pre><span></span><code><a id=__codelineno-1-1 name=__codelineno-1-1 href=#__codelineno-1-1></a><span class=cp>#define LENMODS "hjlLtz"</span>
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<a id=__codelineno-1-2 name=__codelineno-1-2 href=#__codelineno-1-2></a><span class=p>...</span>
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<a id=__codelineno-1-3 name=__codelineno-1-3 href=#__codelineno-1-3></a><span class=cm>/* skip possible format modifiers */</span>
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<a id=__codelineno-1-4 name=__codelineno-1-4 href=#__codelineno-1-4></a><span class=n>modstart</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>fmt</span><span class=p>;</span>
|
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<a id=__codelineno-1-5 name=__codelineno-1-5 href=#__codelineno-1-5></a><span class=k>while</span><span class=w> </span><span class=p>(</span><span class=o>*</span><span class=n>fmt</span><span class=w> </span><span class=o>&&</span><span class=w> </span><span class=n>strchr</span><span class=w> </span><span class=p>(</span><span class=n>LENMODS</span><span class=p>,</span><span class=w> </span><span class=o>*</span><span class=n>fmt</span><span class=p>))</span>
|
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<a id=__codelineno-1-6 name=__codelineno-1-6 href=#__codelineno-1-6></a><span class=n>fmt</span><span class=o>++</span><span class=p>;</span>
|
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</code></pre></div> - mksh has no built-in printf by default (usually). There is an unsupported compile-time option to include a very poor, basically unusable implementation. For the most part you must rely upon the system's <code>/usr/bin/printf</code> or equivalent. The mksh maintainer recommends using <code>print</code>. The development version (post- R40f) adds a new parameter expansion in the form of <code>${name@Q}</code> which fills the role of <code>printf %q</code> -- expanding in a shell-escaped format.</p> <ul> <li>ksh93 optimizes builtins run from within a command substitution and which have no redirections to run in the shell's process. Therefore the <code>printf -v</code> functionality can be closely matched by <code>var=$(printf ...)</code> without a big performance hit.</li> </ul> <div class=highlight><pre><span></span><code><a id=__codelineno-2-1 name=__codelineno-2-1 href=#__codelineno-2-1></a><span class=c1># Illustrates Bash-like behavior. Redefining printf is usually unnecessary / not recommended.</span>
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<a id=__codelineno-2-2 name=__codelineno-2-2 href=#__codelineno-2-2></a><span class=k>function</span><span class=w> </span><span class=nb>printf</span><span class=w> </span><span class=o>{</span>
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<a id=__codelineno-2-3 name=__codelineno-2-3 href=#__codelineno-2-3></a><span class=w> </span><span class=k>case</span><span class=w> </span><span class=nv>$1</span><span class=w> </span><span class=k>in</span>
|
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<a id=__codelineno-2-4 name=__codelineno-2-4 href=#__codelineno-2-4></a><span class=w> </span>-v<span class=o>)</span>
|
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<a id=__codelineno-2-5 name=__codelineno-2-5 href=#__codelineno-2-5></a><span class=w> </span><span class=nb>shift</span>
|
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<a id=__codelineno-2-6 name=__codelineno-2-6 href=#__codelineno-2-6></a><span class=w> </span>nameref<span class=w> </span><span class=nv>x</span><span class=o>=</span><span class=nv>$1</span>
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<a id=__codelineno-2-7 name=__codelineno-2-7 href=#__codelineno-2-7></a><span class=w> </span><span class=nb>shift</span>
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<a id=__codelineno-2-8 name=__codelineno-2-8 href=#__codelineno-2-8></a><span class=w> </span><span class=nv>x</span><span class=o>=</span><span class=k>$(</span><span class=nb>command</span><span class=w> </span><span class=nb>printf</span><span class=w> </span><span class=s2>"</span><span class=nv>$@</span><span class=s2>"</span><span class=k>)</span>
|
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<a id=__codelineno-2-9 name=__codelineno-2-9 href=#__codelineno-2-9></a><span class=w> </span><span class=p>;;</span>
|
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<a id=__codelineno-2-10 name=__codelineno-2-10 href=#__codelineno-2-10></a><span class=w> </span>*<span class=o>)</span>
|
||
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<a id=__codelineno-2-11 name=__codelineno-2-11 href=#__codelineno-2-11></a><span class=w> </span><span class=nb>command</span><span class=w> </span><span class=nb>printf</span><span class=w> </span><span class=s2>"</span><span class=nv>$@</span><span class=s2>"</span>
|
||
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<a id=__codelineno-2-12 name=__codelineno-2-12 href=#__codelineno-2-12></a><span class=w> </span><span class=k>esac</span>
|
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<a id=__codelineno-2-13 name=__codelineno-2-13 href=#__codelineno-2-13></a><span class=o>}</span>
|
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<a id=__codelineno-2-14 name=__codelineno-2-14 href=#__codelineno-2-14></a><span class=nb>builtin</span><span class=w> </span>cut
|
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<a id=__codelineno-2-15 name=__codelineno-2-15 href=#__codelineno-2-15></a>print<span class=w> </span><span class=nv>$$</span>
|
||
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<a id=__codelineno-2-16 name=__codelineno-2-16 href=#__codelineno-2-16></a><span class=nb>printf</span><span class=w> </span>-v<span class=w> </span><span class=s1>'foo[2]'</span><span class=w> </span><span class=s1>'%d\n'</span><span class=w> </span><span class=s2>"</span><span class=k>$(</span>cut<span class=w> </span>-d<span class=w> </span><span class=s1>' '</span><span class=w> </span>-f<span class=w> </span><span class=m>1</span><span class=w> </span>/proc/self/stat<span class=k>)</span><span class=s2>"</span>
|
||
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<a id=__codelineno-2-17 name=__codelineno-2-17 href=#__codelineno-2-17></a><span class=nb>typeset</span><span class=w> </span>-p<span class=w> </span>foo
|
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<a id=__codelineno-2-18 name=__codelineno-2-18 href=#__codelineno-2-18></a><span class=c1># 22461</span>
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<a id=__codelineno-2-19 name=__codelineno-2-19 href=#__codelineno-2-19></a><span class=c1># typeset -a foo=([2]=22461)</span>
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</code></pre></div> <ul> <li>The optional Bash loadable <code>print</code> may be useful for ksh compatibility and to overcome some of <a href=../echo/ >echo</a>'s portability pitfalls. Bash, ksh93, and zsh's <code>print</code> have an <code>-f</code> option which takes a <code>printf</code> format string and applies it to the remaining arguments. Bash lists the synopsis as: <code>print: print [-Rnprs] [-u unit] [-f format] [arguments]</code>. However, only <code>-Rrnfu</code> are actually functional. Internally, <code>-p</code> is a noop (it doesn't tie in with Bash coprocs at all), and <code>-s</code> only sets a flag but has no effect. <code>-Cev</code> are unimplemented.</li> <li>Assigning to variables: The <code>printf -v</code> way is slightly different to the way using command-substitution. <a href=../../../syntax/expansion/cmdsubst/ >Command substitution</a> removes trailing newlines before substituting the text, <code>printf -v</code> preserves all output.</li> </ul> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>SUS: <a href=http://pubs.opengroup.org/onlinepubs/9699919799/utilities/printf.html>printf utility</a> and <a href=http://pubs.opengroup.org/onlinepubs/9699919799/functions/printf.html>printf() function</a></li> <li><a href=../../../snipplets/print_horizontal_line/ >Code snip: Print a horizontal line</a> uses some <code>printf</code> examples</li> <li><a href=http://mywiki.wooledge.org/BashFAQ/018>Greg's BashFAQ 18: How can I use numbers with leading zeros in a loop, e.g., 01, 02?</a></li> </ul> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">November 13, 2024</span> </span> <span class=md-source-file__fact> <span class=md-icon title=Created> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M14.47 15.08 11 13V7h1.5v5.25l3.08 1.83c-.41.28-.79.62-1.11 1m-1.39 4.84c-.36.05-.71.08-1.08.08-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8c0 .37-.03.72-.08 1.08.69.1 1.33.32 1.92.64.1-.56.16-1.13.16-1.72 0-5.5-4.5-10-10-10S2 6.5 2 12s4.47 10 10 10c.59 0 1.16-.06 1.72-.16-.32-.59-.54-1.23-.64-1.92M18 15v3h-3v2h3v3h2v-3h3v-2h-3v-3z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">November 13, 2024</span> </span> </aside> <h2 id=__comments>Comments</h2> <script src=https://giscus.app/client.js data-repo=flokoe/bash-hackers-wiki data-repo-id=R_kgDOJ3Nr6Q data-category="Giscus Page Comments" data-category-id=DIC_kwDOJ3Nr6c4CXq9t data-mapping=pathname data-strict=1 data-reactions-enabled=1 data-emit-metadata=0 data-input-position=top data-theme=preferred_color_scheme data-lang=en data-loading=lazy crossorigin=anonymous async>
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