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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/quoting/ rel=canonical><link href=../pe/ rel=prev><link href=../redirection/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.40"><title>Quotes and escaping - The Bash Hackers Wiki</title><link rel=stylesheet href=../../assets/stylesheets/main.8c3ca2c6.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=#quotes-and-escaping 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> Quotes and escaping </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-color-scheme
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### (1) "my
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### (2) multiword
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### (3) argument"
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MYARG="\"my multiword argument\""
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somecommand $MYARG
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### THIS IS NOT (!) THE SAME AS ###
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command "my multiword argument"
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### YOU NEED ###
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MYARG="my multiword argument"
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command "$MYARG"
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</code></pre></div> <h2 id=per-character-escaping>Per-character escaping<a class=headerlink href=#per-character-escaping title="Permanent link">¶</a></h2> <p>Per-character escaping is useful in on expansions and substitutions. In general, a character that has a special meaning to Bash, like the dollar-sign (<code>$</code>) can be masked to not have a special meaning using the backslash:</p> <div class=highlight><pre><span></span><code>echo \$HOME is set to \"$HOME\"
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</code></pre></div> <ul> <li><code>\$HOME</code> won't expand because it's not in variable-expansion syntax anymore</li> <li>The backslash changes the quotes into literals - otherwise Bash would interpret them</li> </ul> <p>The sequence <code><newline></code> (an unquoted backslash, followed by a <code><newline></code> character) is interpreted as <strong>line continuation</strong>. It is removed from the input stream and thus effectively ignored. Use it to beautify your code:</p> <div class=highlight><pre><span></span><code># escapestr_sed()
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# read a stream from stdin and escape characters in text that could be interpreted as
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# special characters by sed
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escape_sed() {
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sed \
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-e 's/\//\\\//g' \
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-e 's/\&/\\\&/g'
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}
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</code></pre></div> <p>The backslash can be used to mask every character that has a special meaning to bash. <u>Exception:</u> Inside a single-quoted string (see below).</p> <h2 id=weak-quoting>Weak quoting<a class=headerlink href=#weak-quoting title="Permanent link">¶</a></h2> <p>Inside a weak-quoted string there's <strong>no special interpretion of</strong>:</p> <ul> <li>spaces as word-separators (on inital command line splitting and on <a href=../expansion/wordsplit/ >word splitting</a>!)</li> <li>single-quotes to introduce strong-quoting (see below)</li> <li>characters for pattern matching</li> <li>tilde expansion</li> <li>pathname expansion</li> <li>process substitution</li> </ul> <p>Everything else, especially <a href=../pe/ >parameter expansion</a>, is performed!</p> <div class=highlight><pre><span></span><code>ls -l "*"
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</code></pre></div> <p>Will not be expanded. <code>ls</code> gets the literal <code>*</code> as argument. It will, unless you have a file named <code>*</code>, spit out an error.</p> <div class=highlight><pre><span></span><code>echo "Your PATH is: $PATH"
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</code></pre></div> <p>Will work as expected. <code>$PATH</code> is expanded, because it's double (weak) quoted.</p> <p>If a backslash in double quotes ("weak quoting") occurs, there are 2 ways to deal with it</p> <ul> <li>if the baskslash is followed by a character that would have a special meaning even inside double-quotes, the backslash is removed and the following character looses its special meaning</li> <li>if the backslash is followed by a character without special meaning, the backslash is not removed</li> </ul> <p>In particuar this means that <code>"\$"</code> will become <code>$</code>, but <code>"\x"</code> will become <code>\x</code>.</p> <h2 id=strong-quoting>Strong quoting<a class=headerlink href=#strong-quoting title="Permanent link">¶</a></h2> <p>Strong quoting is very easy to explain:</p> <p>Inside a single-quoted string <strong>nothing</strong> is interpreted, except the single-quote that closes the string.</p> <div class=highlight><pre><span></span><code>echo 'Your PATH is: $PATH'
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</code></pre></div> <p><code>$PATH</code> won't be expanded, it's interpreted as ordinary text because it's surrounded by strong quotes.</p> <p>In practise that means, to produce a text like <code>Here's my test...</code> as a single-quoted string, you have to leave and re-enter the single quoting to get the character "<code>'</code>" as literal text:</p> <div class=highlight><pre><span></span><code># WRONG
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echo 'Here's my test...'
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# RIGHT
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echo 'Here'\''s my test...'
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# ALTERNATIVE: It's also possible to mix-and-match quotes for readability:
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echo "Here's my test"
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</code></pre></div> <h2 id=ansi-c-like-strings>ANSI C like strings<a class=headerlink href=#ansi-c-like-strings title="Permanent link">¶</a></h2> <p>Bash provides another quoting mechanism: Strings that contain ANSI C-like escape sequences. The Syntax is:</p> <div class=highlight><pre><span></span><code>$'string'
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</code></pre></div> <p>where the following escape sequences are decoded in <code>string</code>:</p> <table> <thead> <tr> <th>Code</th> <th>Meaning</th> </tr> </thead> <tbody> <tr> <td><code>\"</code></td> <td>double-quote</td> </tr> <tr> <td><code>\'</code></td> <td>single-quote</td> </tr> <tr> <td><code>\\</code></td> <td>backslash</td> </tr> <tr> <td><code>\a</code></td> <td>terminal alert character (bell)</td> </tr> <tr> <td><code>\b</code></td> <td>backspace</td> </tr> <tr> <td><code>\e</code></td> <td>escape (ASCII 033)</td> </tr> <tr> <td><code>\E</code></td> <td>escape (ASCII 033) <strong>\E is non-standard</strong></td> </tr> <tr> <td><code>\f</code></td> <td>form feed</td> </tr> <tr> <td><code>\n</code></td> <td>newline</td> </tr> <tr> <td><code>\r</code></td> <td>carriage return</td> </tr> <tr> <td><code>\t</code></td> <td>horizontal tab</td> </tr> <tr> <td><code>\v</code></td> <td>vertical tab</td> </tr> <tr> <td><code>\cx</code></td> <td>a control-x character, for example, <code>$'\cZ'</code> to print the control sequence composed of Ctrl-Z (<code>^Z</code>)</td> </tr> <tr> <td><code>\uXXXX</code></td> <td>Interprets <code>XXXX</code> as a hexadecimal number and prints the corresponding character from the character set (4 digits) (Bash 4.2-alpha)</td> </tr> <tr> <td><code>\UXXXXXXXX</code></td> <td>Interprets <code>XXXX</code> as a hexadecimal number and prints the corresponding character from the character set (8 digits) (Bash 4.2-alpha)</td> </tr> <tr> <td><code>\nnn</code></td> <td>the eight-bit character whose value is the octal value nnn (one to three digits)</td> </tr> <tr> <td><code>\xHH</code></td> <td>the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)</td> </tr> </tbody> </table> <p>This is especially useful when you want to pass special characters as arguments to some programs, like passing a newline to sed.</p> <p>The resulting text is treated as if it were <strong>single-quoted</strong>. No further expansion happens.</p> <p>The <code>$'...'</code> syntax comes from ksh93, but is portable to most modern shells including pdksh. A <a href="http://austingroupbugs.net/view.php?id=249#c590">specification</a> for it was accepted for SUS issue 7. There are still some stragglers, such as most ash variants including dash, (except busybox built with "bash compatibility" features).</p> <h2 id=i18nl10n>I18N/L10N<a class=headerlink href=#i18nl10n title="Permanent link">¶</a></h2> <p>A dollar-sign followed by a double-quoted string, for example</p> <div class=highlight><pre><span></span><code>echo $"generating database..."
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</code></pre></div> <p>means I18N. If there is a translation available for that string, it is used instead of the given text. If not, or if the locale is <code>C</code>/<code>POSIX</code>, the dollar sign is simply ignored, which results in a normal double quoted string.</p> <p>If the string was replaced (translated), the result is double quoted.</p> <p>In case you're a C programmer: The purpose of <code>$"..."</code> is the same as for <code>gettext()</code> or <code>_()</code>.</p> <p>For useful examples to localize your scripts, please see <a href=http://tldp.org/LDP/abs/html/localization.html>Appendix I of the Advanced Bash Scripting Guide</a>.</p> <p><strong>Attention:</strong> There is a security hole. Please read <a href=http://www.gnu.org/software/gettext/manual/html_node/bash.html>the gettext documentation</a></p> <h2 id=common-mistakes>Common mistakes<a class=headerlink href=#common-mistakes title="Permanent link">¶</a></h2> <h3 id=string-lists-in-for-loops>String lists in for-loops<a class=headerlink href=#string-lists-in-for-loops title="Permanent link">¶</a></h3> <p>The <a href=../ccmd/classic_for/ >classic for loop</a> uses a list of words to iterate through. The list can also be in a variable:</p> <div class=highlight><pre><span></span><code>mylist="DOG CAT BIRD HORSE"
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</code></pre></div> <p><strong><u>WRONG</u></strong> way to iterate through this list:</p> <div class=highlight><pre><span></span><code>for animal in "$mylist"; do
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echo $animal
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done
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</code></pre></div> <p>Why? Due to the double-quotes, technically, the expansion of <code>$mylist</code> is seen as <strong>one word</strong>. The for loop iterates exactly one time, with <code>animal</code> set to the whole list.</p> <p><strong><u>RIGHT</u></strong> way to iterate through this list:</p> <div class=highlight><pre><span></span><code>for animal in $mylist; do
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echo $animal
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done
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</code></pre></div> <h3 id=working-out-the-test-command>Working out the test-command<a class=headerlink href=#working-out-the-test-command title="Permanent link">¶</a></h3> <p>The command <code>test</code> or <code>[ ... ]</code> (<a href=../../commands/classictest/ >the classic test command</a>) is an ordinary command, so ordinary syntax rules apply. Let's take string comparison as an example:</p> <div class=highlight><pre><span></span><code>[ WORD = WORD ]
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</code></pre></div> <p>The <code>]</code> at the end is a convenience; if you type <code>which [</code> you will see that there is in fact a binary file with that name. So if we were writing this as a test command it would be:</p> <div class=highlight><pre><span></span><code>test WORD = WORD
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</code></pre></div> <p>When you compare variables, it's wise to quote them. Let's create a test string with spaces:</p> <div class=highlight><pre><span></span><code>mystring="my string"
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</code></pre></div> <p>And now check that string against the word "testword":</p> <div class=highlight><pre><span></span><code>[ $mystring = testword ] # WRONG!
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</code></pre></div> <p>This fails! These are too many arguments for the string comparison test. After expansion is performed, you really execute:</p> <div class=highlight><pre><span></span><code>[ my string = testword ]
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test my string = testword
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</code></pre></div> <p>Which is wrong, because <code>my</code> and <code>string</code> are two separate arguments.</p> <p>So what you really want to do is:</p> <div class=highlight><pre><span></span><code>[ "$mystring" = testword ] # RIGHT!
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test 'my string' = testword
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</code></pre></div> <p>Now the command has three parameters, which makes sense for a binary (two argument) operator.</p> <p><strong><u>Hint:</u></strong> Inside the <a href=../ccmd/conditional_expression/ >conditional expression</a> (<code>[[ ]]</code>) Bash doesn't perform word splitting, and thus you don't need to quote your variable references - they are always seen as "one word".</p> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>Internal: <a href=../words/ >Some words about words...</a></li> <li>Internal: <a href=../expansion/wordsplit/ >Word splitting</a></li> <li>Internal: <a href=../expansion/intro/ >Introduction to expansions and substitutions</a></li> <li>External: <a href=http://www.grymoire.com/Unix/Quote.html>Grymore: Shellquoting</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">October 12, 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">October 12, 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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