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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/declare/ rel=canonical><link href=../cd/ rel=prev><link href=../echo/ 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 declare builtin 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-declare-builtin-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 declare builtin 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){v
# obsolete typeset synonym
typeset [-aAfFgilnrtux] [-p] [NAME[=VALUE] ...]
</code></pre></div> <h2 id=description>Description<a class=headerlink href=#description title="Permanent link">&para;</a></h2> <p><code>declare</code> is used to display or set variables along with variable attributes. When used to display variables/functions and their value, the output is re-usable as input for the shell.</p> <p>If no <code>NAME</code> is given, it displays the values of all variables or functions when restricted by the <code>-f</code> option.</p> <p>If <code>NAME</code> is followed by <code>=VALUE</code>, <code>declare</code> also sets the value for a variable.</p> <p>When used in a function, <code>declare</code> makes <code>NAMEs</code> local variables, unless used with the <code>-g</code> option.</p> <p>Don't use it's synonym <code>typeset</code> when coding for Bash, since it's tagged as obsolete.</p> <h3 id=options>Options<a class=headerlink href=#options title="Permanent link">&para;</a></h3> <p>Below, <code>[-+]X</code> indicates an attribute, use <code>-X</code> to set the attribute, <code>+X</code> to remove it.</p> <table> <thead> <tr> <th>Option</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>[-+]a</code></td> <td>make NAMEs indexed arrays (removing with <code>+a</code> is valid syntax, but leads to an error message)</td> </tr> <tr> <td><code>[-+]A</code></td> <td>make NAMEs associative arrays</td> </tr> <tr> <td><code>[-+]c</code></td> <td><strong>Undocumented</strong> convert NAMEs to "capcase" on assignment (makes the first letter upper-case and the rest lower). Requires Bash built with <code>-DCASEMOD_CAPCASE</code></td> </tr> <tr> <td><code>-f</code></td> <td>restrict action or display to function names and definitions (removing with <code>+f</code> is valid syntax, but leads to an error message)</td> </tr> <tr> <td><code>-F</code></td> <td>restrict display to function names only (plus line number and source file when debugging)</td> </tr> <tr> <td><code>-g</code></td> <td>create global variables when used in a shell function; otherwise ignored (by default, <code>declare</code> declares local scope variables when used in shell functions)</td> </tr> <tr> <td><code>[-+]i</code></td> <td>make NAMEs have the "integer" attribute</td> </tr> <tr> <td><code>[-+]l</code></td> <td>convert NAMEs to lower case on assignment (makes sure the variable contains only lower case letters)</td> </tr> <tr> <td><code>[-+]n</code></td> <td>make NAME a reference to the variable named by its value. Introduced in Bash 4.3-alpha. ''<code>${!NAME}</code>'' reveals the reference variable name, VALUE. Use <code>unset -n NAME</code> to unset the variable. (<code>unset -v NAME</code> unsets the VALUE variable.) Use <code>[[ -R NAME ]]</code> to test if NAME has been set to a VALUE, another variable's name.</td> </tr> <tr> <td><code>-p</code></td> <td>display the attributes and value of each NAME</td> </tr> <tr> <td><code>[-+]r</code></td> <td>make NAMEs readonly (removing with <code>+r</code> is valid syntax, but not possible)</td> </tr> <tr> <td><code>[-+]t</code></td> <td>make NAMEs have the "trace" attribute (effective only for functions)</td> </tr> <tr> <td><code>[-+]u</code></td> <td>convert NAMEs to upper case on assignment (makes sure the variable contains only upper case letters)</td> </tr> <tr> <td><code>[-+]x</code></td> <td>make NAMEs exported</td> </tr> </tbody> </table> <h3 id=return-status>Return status<a class=headerlink href=#return-status title="Permanent link">&para;</a></h3> <table> <thead> <tr> <th>Status</th> <th>Reason</th> </tr> </thead> <tbody> <tr> <td>0</td> <td>no error</td> </tr> <tr> <td>!= 0</td> <td>invalid option</td> </tr> <tr> <td>!= 0</td> <td>invalid variable name given</td> </tr> <tr> <td>!= 0</td> <td>attempt to <strong>define</strong> a function using <code>-f</code></td> </tr> <tr> <td>!= 0</td> <td>assignment to a readonly variable</td> </tr> <tr> <td>!= 0</td> <td>removing the readonly-attribute from a readonly variable</td> </tr> <tr> <td>!= 0</td> <td>assignment to an array variable without the compound assignment syntax (<code>array=(...)</code>)</td> </tr>
foo ()
{
echo &quot;FOO is BAR&quot;
}
world ()
{
echo &quot;Hello World!&quot;
}
</code></pre></div> <p>...or just a specific defined function.</p> <div class=highlight><pre><span></span><code>$ declare -f foo
foo ()
{
echo &quot;FOO is BAR&quot;
}
</code></pre></div> <h3 id=nameref>Nameref<a class=headerlink href=#nameref title="Permanent link">&para;</a></h3> <p>Bash 4.3 adds a new way to indirectly reference variables. <code>typeset -n</code> or <code>declare -n</code> can be used to make a variable indirectly refer to another. In Bash, the lvalue of the assignment given to <code>typeset -n</code> or <code>declare -n</code> will refer to the variable whose name is expanded on the RHS.</p> <p><code>typeset -n</code> is used in the example below. See notes below.</p> <div class=highlight><pre><span></span><code># Sum a set of arrays and assign the result indirectly, also printing each intermediary result (without portability workarounds)
# sum name arrname [ arrname ... ]
function sum {
typeset -n _result=$1 _arr
typeset IFS=+
_result=0
for _arr in &quot;${@:2}&quot;; do # Demonstrate the special property of &quot;for&quot; on a nameref.
(( _result += ${_arr[*]} ))
printf &#39;%s = %d\n&#39; &quot;${!_result}&quot; &quot;$_result&quot; # Demonstrate the special property of ${!ref} on a nameref.
done
}
a=(1 2 3) b=(6 5 4) c=(2 4 6)
sum total a b c
printf &#39;Final value of &quot;total&quot; is: %d\n&#39; &quot;$total&quot;
</code></pre></div> <div hide> function sum { typeset -n _result=$1 shift typeset IFS=+ _arrx _result=0 for _arrx in "$@"; do # Demonstrate the special property of "for" on a nameref. typeset -n _arr=$_arrx (( _result += ${_arr[*]} )) printf '%s = %d\n' "${!_result}" "$_result" # Demonstrate the special property of ${!ref} on a nameref. done } a=(1 2 3); b=(6 5 4); c=(2 4 6) sum total a b c printf \'Final value of \"total\" is: %d\\n\' \"\$total\" </div> <p><code>typeset -n</code> is currently implemented in ksh93, mksh, and Bash 4.3. Bash and mksh's implementations are quite similar, but much different from ksh93's. See <a href=#portability_considerations>Portability considerations</a> for details. ksh93 namerefs are much more powerful than Bash's.</p> <h2 id=portability-considerations>Portability considerations<a class=headerlink href=#portability-considerations title="Permanent link">&para;</a></h2> <ul> <li><code>declare</code> is not specified by POSIX&reg;</li> <li><code>declare</code> is unique to Bash and totally non-portable with the possible exception of Zsh in Bash compatibility mode. Bash marks the synonym <code>typeset</code> as obsolete, which in Bash behaves identically to <code>declare</code>. All other Korn-like shells use <code>typeset</code>, so it probably isn't going away any time soon. Unfortunately, being a non-standard builtin, <code>typeset</code> differs significantly between shells. ksh93 also considers <code>typeset</code> a special builtin, while Bash does not - even in POSIX mode. If you use <code>typeset</code>, you should attempt to only use it in portable ways.</li> <li><strong>todo</strong> nameref portability...</li> </ul> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../../syntax/arrays/ >arrays</a></li> <li><a href=../readonly/ >readonly</a></li> <li><a href=../unset/ >unset</a></li> <li><a href="http://austingroupbugs.net/view.php?id=351">declaration commands</a> will change the behavior of certain builtins such as <code>export</code> in the next version of POSIX.</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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