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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/syntax/expansion/brace/ rel=canonical><link href=../arith/ rel=prev><link href=../cmdsubst/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.44"><title>Brace expansion - 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=#brace-expansion 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> Brace expansion </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("(prefers-c
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{<START>..<END>}
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{<START>..<END>..<INCR>} (Bash 4)
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<PREFIX>{........}
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{........}<SUFFIX>
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<PREFIX>{........}<SUFFIX>
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</code></pre></div> <p>Brace expansion is used to generate arbitrary strings. The specified strings are used to generate <strong>all possible combinations</strong> with the optional surrounding prefixes and suffixes.</p> <p>Usually it's used to generate mass-arguments for a command, that follow a specific naming-scheme.</p> <p>:!: It is the very first step in expansion-handling, it's important to understand that. When you use</p> <div class=highlight><pre><span></span><code>echo {a,b}$PATH
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</code></pre></div> <p>then the brace expansion <strong>does not expand the variable</strong> - this is done in a <strong>later step</strong>. Brace expansion just makes it being:</p> <div class=highlight><pre><span></span><code>echo a$PATH b$PATH
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</code></pre></div> <p>Another common pitfall is to assume that a range like <code>{1..200}</code> can be expressed with variables using <code>{$a..$b}</code>. Due to what I described above, it <strong>simply is not possible</strong>, because it's the very first step in doing expansions. A possible way to achieve this, if you really can't handle this in another way, is using the <code>eval</code> command, which basically evaluates a commandline twice: <code>eval echo {$a..$b}</code> For instance, when embedded inside a for loop : <code>for i in $(eval echo {$a..$b})</code> This requires that the entire command be properly escaped to avoid unexpected expansions. If the sequence expansion is to be assigned to an array, another method is possible using <a href=../../../commands/builtin/declare/ >declaration commands</a>: <code>declare -a 'pics=(img{'"$a..$b"'}.png)'; mv "${pics[@]}" ../imgs</code> This is significantly safer, but one must still be careful to control the values of <code>$a</code> and <code>$b</code>. Both the exact quoting, and explicitly including "<code>-a</code>" are important.</p> <p>The brace expansion is present in two basic forms, <strong>string lists</strong> and <strong>ranges</strong>.</p> <p>It can be switched on and off under runtime by using the <code>set</code> builtin and the option <code>-B</code> and <code>+B</code> or the long option <code>braceexpand</code>. If brace expansion is enabled, the stringlist in <code>SHELLOPTS</code> contains <code>braceexpand</code>.</p> <h2 id=string-lists>String lists<a class=headerlink href=#string-lists title="Permanent link">¶</a></h2> <div class=highlight><pre><span></span><code>{string1,string2,...,stringN}
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</code></pre></div> <p>Without the optional prefix and suffix strings, the result is just a space-separated list of the given strings:</p> <div class=highlight><pre><span></span><code>$ echo {I,want,my,money,back}
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I want my money back
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</code></pre></div> <p>With prefix or suffix strings, the result is a space-separated list of <strong>all possible combinations</strong> of prefix or suffix specified strings:</p> <div class=highlight><pre><span></span><code>$ echo _{I,want,my,money,back}
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_I _want _my _money _back
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$ echo {I,want,my,money,back}_
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I_ want_ my_ money_ back_
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$ echo _{I,want,my,money,back}-
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_I- _want- _my- _money- _back-
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</code></pre></div> <p>The brace expansion is only performed, if the given string list is really a <strong>list of strings</strong>, i.e., if there is a minimum of one "<code>,</code>" (comma)! Something like <code>{money}</code> doesn't expand to something special, it's really only the text "<code>{money}</code>".</p> <h2 id=ranges>Ranges<a class=headerlink href=#ranges title="Permanent link">¶</a></h2> <div class=highlight><pre><span></span><code>{<START>..<END>}
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</code></pre></div> <p>Brace expansion using ranges is written giving the startpoint and the endpoint of the range. This is a "sequence expression". The sequences can be of two types</p> <ul> <li>integers (optionally zero padded, optionally with a given increment)</li> <li> <p>characters</p> <p>$ echo {5..12} 5 6 7 8 9 10 11 12</p> <p>$ echo {c..k} c d e f g h i j k</p> </li> </ul> <p>When you mix these both types, brace expansion is <strong>not</strong> performed:</p> <div class=highlight><pre><span></span><code>$ echo {5..k}
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{5..k}
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</code></pre></div> <p>When you zero pad one of the numbers (or both) in a range, then the generated range is zero padded, too:</p> <div class=highlight><pre><span></span><code>$ echo {01..10}
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01 02 03 04 05 06 07 08 09 10
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</code></pre></div> <p>There's a chapter of Bash 4 brace expansion changes at <a href=#new_in_bash_4.0>the end of this article</a>.</p> <p>Similar to the expansion using stringlists, you can add prefix and suffix strings:</p> <div class=highlight><pre><span></span><code>$ echo 1.{0..9}
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1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
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$ echo ---{A..E}---
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---A--- ---B--- ---C--- ---D--- ---E---
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</code></pre></div> <h2 id=combining-and-nesting>Combining and nesting<a class=headerlink href=#combining-and-nesting title="Permanent link">¶</a></h2> <p>When you combine more brace expansions, you effectively use a brace expansion as prefix or suffix for another one. Let's generate all possible combinations of uppercase letters and digits:</p> <div class=highlight><pre><span></span><code>$ echo {A..Z}{0..9}
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A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 C0 C1 C2 C3 C4 C5 C6
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C7 C8 C9 D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 F0 F1 F2 F3
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F4 F5 F6 F7 F8 F9 G0 G1 G2 G3 G4 G5 G6 G7 G8 G9 H0 H1 H2 H3 H4 H5 H6 H7 H8 H9 I0
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I1 I2 I3 I4 I5 I6 I7 I8 I9 J0 J1 J2 J3 J4 J5 J6 J7 J8 J9 K0 K1 K2 K3 K4 K5 K6 K7
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K8 K9 L0 L1 L2 L3 L4 L5 L6 L7 L8 L9 M0 M1 M2 M3 M4 M5 M6 M7 M8 M9 N0 N1 N2 N3 N4
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N5 N6 N7 N8 N9 O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 Q0 Q1
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Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 R0 R1 R2 R3 R4 R5 R6 R7 R8 R9 S0 S1 S2 S3 S4 S5 S6 S7 S8
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S9 T0 T1 T2 T3 T4 T5 T6 T7 T8 T9 U0 U1 U2 U3 U4 U5 U6 U7 U8 U9 V0 V1 V2 V3 V4 V5
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V6 V7 V8 V9 W0 W1 W2 W3 W4 W5 W6 W7 W8 W9 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 Y0 Y1 Y2
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Y3 Y4 Y5 Y6 Y7 Y8 Y9 Z0 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9
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</code></pre></div> <p>Hey.. that <strong>saves you writing</strong> 260 strings!</p> <p>Brace expansions can be nested, but too much of it usually makes you losing overview a bit ;-)</p> <p>Here's a sample to generate the alphabet, first the uppercase letters, then the lowercase ones:</p> <div class=highlight><pre><span></span><code>$ echo {{A..Z},{a..z}}
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z
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</code></pre></div> <h2 id=common-use-and-examples>Common use and examples<a class=headerlink href=#common-use-and-examples title="Permanent link">¶</a></h2> <h3 id=massdownload-from-the-web>Massdownload from the Web<a class=headerlink href=#massdownload-from-the-web title="Permanent link">¶</a></h3> <p>In this example, <code>wget</code> is used to download documentation that is split over several numbered webpages.</p> <p><code>wget</code> won't see your braces. It will see <strong>6 different URLs</strong> to download.</p> <div class=highlight><pre><span></span><code>wget http://docs.example.com/documentation/slides_part{1,2,3,4,5,6}.html
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</code></pre></div> <p>Of course it's possible, and even easier, to do that with a sequence:</p> <div class=highlight><pre><span></span><code>wget http://docs.example.com/documentation/slides_part{1..6}.html
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</code></pre></div> <h3 id=generate-a-subdirectory-structure>Generate a subdirectory structure<a class=headerlink href=#generate-a-subdirectory-structure title="Permanent link">¶</a></h3> <p>Your life is hard? Let's ease it a bit - that's what shells are here for.</p> <div class=highlight><pre><span></span><code>mkdir /home/bash/test/{foo,bar,baz,cat,dog}
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</code></pre></div> <h3 id=generate-numbers-with-a-prefix-001-002>Generate numbers with a prefix 001 002 ...<a class=headerlink href=#generate-numbers-with-a-prefix-001-002 title="Permanent link">¶</a></h3> <ul> <li> <p>Using a prefix:</p> <p>for i in 0{1..9} 10; do printf "%s\n" "$i";done</p> </li> </ul> <p>If you need to create words with the number embedded, you can use nested brace:</p> <div class=highlight><pre><span></span><code>printf "%s\n" img{00{1..9},0{10..99},{100..999}}.png
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</code></pre></div> <ul> <li> <p>Formatting the numbers with printf:</p> <p>echo $(printf "img%02d.png " {1..99})</p> </li> </ul> <p>See the <a href=#news_in_bash_4.0>text below</a> for a new Bash 4 method.</p> <h3 id=repeating-arguments-or-words>Repeating arguments or words<a class=headerlink href=#repeating-arguments-or-words title="Permanent link">¶</a></h3> <div class=highlight><pre><span></span><code>somecommand -v -v -v -v -v
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</code></pre></div> <p>Can be written as</p> <div class=highlight><pre><span></span><code>somecommand -v{,,,,}
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</code></pre></div> <p>...which is a kind of a hack, but hey, it works.</p> <div class="admonition info"> <p class=admonition-title>More fun</p> <p>The most optimal possible brace expansion to expand n arguments of course consists of n's prime factors. We can use the "factor" program bundled with GNU coreutils to emit a brace expansion that will expand any number of arguments.</p> <div class=highlight><pre><span></span><code>function braceify {
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[[ $1 == +([[:digit:]]) ]] || return
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typeset -a a
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read -ra a < <(factor "$1")
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eval "echo $(printf '{$(printf ,%%.s {1..%s})}' "${a[@]:1}")"
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}
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printf 'eval printf "$arg"%s' "$(braceify 1000000)"
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</code></pre></div> <p>"Braceify" generates the expansion code itself. In this example we inject that output into a template which displays the most terse brace expansion code that would expand <code>"$arg"</code> 1,000,000 times if evaluated. In this case, the output is:</p> <div class=highlight><pre><span></span><code>eval printf "$arg"{,,}{,,}{,,}{,,}{,,}{,,}{,,,,,}{,,,,,}{,,,,,}{,,,,,}{,,,,,}{,,,,,}
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</code></pre></div> </div> <h2 id=new-in-bash-40>New in Bash 4.0<a class=headerlink href=#new-in-bash-40 title="Permanent link">¶</a></h2> <h3 id=zero-padded-number-expansion>Zero padded number expansion<a class=headerlink href=#zero-padded-number-expansion title="Permanent link">¶</a></h3> <p>Prefix either of the numbers in a numeric range with <code>0</code> to pad the expanded numbers with the correct amount of zeros:</p> <div class=highlight><pre><span></span><code>$ echo {0001..5}
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0001 0002 0003 0004 0005
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</code></pre></div> <h3 id=increment>Increment<a class=headerlink href=#increment title="Permanent link">¶</a></h3> <p>It is now possible to specify an increment using ranges:</p> <div class=highlight><pre><span></span><code>{<START>..<END>..<INCR>}
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</code></pre></div> <p><code><INCR></code> is numeric, you can use a negative integer but the correct sign is deduced from the order of <code><START></code> and <code><END></code> anyways.</p> <div class=highlight><pre><span></span><code>$ echo {1..10..2}
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1 3 5 7 9
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$ echo {10..1..2}
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10 8 6 4 2
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</code></pre></div> <p>Interesting feature: The increment specification also works for letter-ranges:</p> <div class=highlight><pre><span></span><code>$ echo {a..z..3}
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a d g j m p s v y
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</code></pre></div> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../intro/ >Introduction to expansion and substitution</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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