mirror of
https://github.com/rawiriblundell/wiki.bash-hackers.org
synced 2024-11-02 00:53:07 +01:00
447 lines
30 KiB
Plaintext
447 lines
30 KiB
Plaintext
|
<!DOCTYPE html>
|
||
|
|
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" dir="ltr" class="no-js">
|
||
|
|
<head><script type="text/javascript" src="/_static/js/bundle-playback.js?v=TPXmWR5s" charset="utf-8"></script>
|
||
|
|
<script type="text/javascript" src="/_static/js/wombat.js?v=txqj7nKC" charset="utf-8"></script>
|
||
|
|
<script type="text/javascript">
|
||
|
|
__wm.init("http://web.archive.org/web");
|
||
|
|
__wm.wombat("https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=edit","20220706152308","http://web.archive.org/","web","/_static/",
|
||
|
|
"1657120988");
|
||
|
|
</script>
|
||
|
|
<link rel="stylesheet" type="text/css" href="/_static/css/banner-styles.css?v=S1zqJCYt" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="/_static/css/iconochive.css?v=qtvMKcIJ" />
|
||
|
|
<!-- End Wayback Rewrite JS Include -->
|
||
|
|
|
||
|
|
<meta charset="UTF-8"/>
|
||
|
|
<title>Command substitution [Bash Hackers Wiki]</title>
|
||
|
|
<script>(function(H){H.className=H.className.replace(/\bno-js\b/,'js')})(document.documentElement)</script>
|
||
|
|
<meta name="viewport" content="width=device-width,initial-scale=1"/>
|
||
|
|
<link rel="shortcut icon" href="/web/20220706152308im_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/images/favicon.ico"/>
|
||
|
|
<link rel="apple-touch-icon" href="/web/20220706152308im_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/images/apple-touch-icon.png"/>
|
||
|
|
<meta name="generator" content="DokuWiki"/>
|
||
|
|
<meta name="robots" content="noindex,nofollow"/>
|
||
|
|
<link type="text/css" rel="stylesheet" href="/web/20220706152308cs_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/assets/bootstrap/default/bootstrap.min.css"/>
|
||
|
|
<link rel="search" type="application/opensearchdescription+xml" href="/web/20220706152308/https://wiki.bash-hackers.org/lib/exe/opensearch.php" title="Bash Hackers Wiki"/>
|
||
|
|
<link rel="start" href="/"/>
|
||
|
|
<link rel="contents" href="/syntax/expansion/cmdsubst?do=index" title="Sitemap"/>
|
||
|
|
<link rel="manifest" href="/web/20220706152308/https://wiki.bash-hackers.org/lib/exe/manifest.php"/>
|
||
|
|
<link rel="alternate" type="application/rss+xml" title="Recent Changes" href="/web/20220706152308/https://wiki.bash-hackers.org/feed.php"/>
|
||
|
|
<link rel="alternate" type="application/rss+xml" title="Current namespace" href="/web/20220706152308/https://wiki.bash-hackers.org/feed.php?mode=list&ns=syntax:expansion"/>
|
||
|
|
<link rel="alternate" type="text/html" title="Plain HTML" href="/web/20220706152308/https://wiki.bash-hackers.org/_export/xhtml/syntax/expansion/cmdsubst"/>
|
||
|
|
<link rel="alternate" type="text/plain" title="Wiki Markup" href="/web/20220706152308/https://wiki.bash-hackers.org/_export/raw/syntax/expansion/cmdsubst"/>
|
||
|
|
<link rel="stylesheet" type="text/css" href="/web/20220706152308cs_/https://wiki.bash-hackers.org/lib/exe/css.php?t=bootstrap3&tseed=54923c3deda180f2db5bd755cd8fbf1a"/>
|
||
|
|
<!--[if gte IE 9]><!-->
|
||
|
|
<script type="text/javascript">/*<![CDATA[*/var NS='syntax:expansion';var JSINFO = {"updatable":1,"userreplace":1,"default_macro_string":"","plugins":{"edittable":{"default columnwidth":""}},"move_renameokay":false,"isadmin":0,"isauth":0,"bootstrap3":{"mode":"source","toc":[],"config":{"collapsibleSections":0,"fixedTopNavbar":1,"showSemanticPopup":0,"sidebarOnNavbar":0,"tagsOnTop":1,"tocAffix":1,"tocCollapseOnScroll":1,"tocCollapsed":0,"tocLayout":"default","useAnchorJS":1,"useAlternativeToolbarIcons":1}},"id":"syntax:expansion:cmdsubst","namespace":"syntax:expansion","ACT":"source","useHeadingNavigation":1,"useHeadingContent":1};
|
||
|
|
/*!]]>*/</script>
|
||
|
|
<script type="text/javascript" charset="utf-8" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/exe/jquery.php?tseed=23f888679b4f1dc26eef34902aca964f"></script>
|
||
|
|
<script type="text/javascript" charset="utf-8" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/exe/js.php?t=bootstrap3&tseed=54923c3deda180f2db5bd755cd8fbf1a"></script>
|
||
|
|
<script type="text/javascript">/*<![CDATA[*/if (typeof IconifyConfig == 'undefined') { var IconifyConfig = { 'defaultAPI' : '/lib/tpl/bootstrap3/iconify.php?prefix={prefix}&icons={icons}' } }
|
||
|
|
/*!]]>*/</script>
|
||
|
|
<script type="text/javascript" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/assets/bootstrap/js/bootstrap.min.js"></script>
|
||
|
|
<script type="text/javascript" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/assets/anchorjs/anchor.min.js"></script>
|
||
|
|
<script type="text/javascript" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/assets/typeahead/bootstrap3-typeahead.min.js"></script>
|
||
|
|
<script type="text/javascript" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/assets/iconify/iconify.min.js"></script>
|
||
|
|
<script type="text/javascript" src="/web/20220706152308js_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/assets/iconify/plugins/fa.js"></script>
|
||
|
|
<!--<![endif]-->
|
||
|
|
<style type="text/css">@media screen { body { margin-top: 65px; } #dw__toc.affix { top: 55px; position: fixed !important; } #dw__toc .nav .nav .nav { display: none; } }</style>
|
||
|
|
<!--[if lt IE 9]>
|
||
|
|
<script type="text/javascript" src="https://oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"></script>
|
||
|
|
<script type="text/javascript" src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
|
||
|
|
<![endif]-->
|
||
|
|
</head>
|
||
|
|
<body class="default dokuwiki mode_source tpl_bootstrap3 dw-page-on-panel dw-fluid-container" data-page-id="syntax:expansion:cmdsubst"><div class="dokuwiki">
|
||
|
|
<header id="dokuwiki__header" class="dw-container dokuwiki container-fluid mx-5">
|
||
|
|
<!-- navbar -->
|
||
|
|
<nav id="dw__navbar" class="navbar navbar-fixed-top navbar-default" role="navigation">
|
||
|
|
|
||
|
|
<div class="dw-container container-fluid mx-5">
|
||
|
|
|
||
|
|
<div class="navbar-header">
|
||
|
|
|
||
|
|
<button class="navbar-toggle" type="button" data-toggle="collapse" data-target=".navbar-collapse">
|
||
|
|
<span class="icon-bar"></span>
|
||
|
|
<span class="icon-bar"></span>
|
||
|
|
<span class="icon-bar"></span>
|
||
|
|
</button>
|
||
|
|
|
||
|
|
<a class="navbar-brand d-flex align-items-center" href="/web/20220706152308/https://wiki.bash-hackers.org/start" accesskey="h" title="Bash Hackers Wiki"><img id="dw__logo" class="pull-left h-100 mr-4" alt="Bash Hackers Wiki" src="/web/20220706152308im_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/images/logo.png"/><div class="pull-right"><div id="dw__title">Bash Hackers Wiki</div></div></a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="collapse navbar-collapse">
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<div class="navbar-right" id="dw__navbar_items">
|
||
|
|
|
||
|
|
|
||
|
|
<!-- navbar-searchform -->
|
||
|
|
<form action="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst" accept-charset="utf-8" class="navbar-form navbar-left search" id="dw__search" method="get" role="search">
|
||
|
|
<div class="input-group">
|
||
|
|
<input id="qsearch" autocomplete="off" type="search" placeholder="Search" value="" accesskey="f" name="q" class="form-control" title="[F]"/>
|
||
|
|
<div class="input-group-btn">
|
||
|
|
<button class="btn btn-default" type="submit" title="Search">
|
||
|
|
<span class="iconify" data-icon="mdi:magnify"></span> </button>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
<input type="hidden" name="do" value="search"/>
|
||
|
|
</form>
|
||
|
|
<!-- /navbar-searchform -->
|
||
|
|
<!-- tools-menu -->
|
||
|
|
<ul class="nav navbar-nav dw-action-icon" id="dw__tools">
|
||
|
|
|
||
|
|
|
||
|
|
<li class="dropdown">
|
||
|
|
|
||
|
|
<a href="" class="dropdown-toggle" data-target="#" data-toggle="dropdown" title="" role="button" aria-haspopup="true" aria-expanded="false">
|
||
|
|
<span class="iconify" data-icon="mdi:wrench"></span> <span class="hidden-lg hidden-md hidden-sm">Tools</span> <span class="caret"></span>
|
||
|
|
</a>
|
||
|
|
|
||
|
|
<ul class="dropdown-menu tools" role="menu">
|
||
|
|
|
||
|
|
<li class="dropdown-header">
|
||
|
|
<span class="iconify" data-icon="mdi:account"></span> User Tools </li>
|
||
|
|
|
||
|
|
<li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=register" title="Register" rel="nofollow" class="menuitem register"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M15 14c-2.67 0-8 1.33-8 4v2h16v-2c0-2.67-5.33-4-8-4m-9-4V7H4v3H1v2h3v3h2v-3h3v-2m6 2a4 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 4z"/></svg><span>Register</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=login&sectok=" title="Log In" rel="nofollow" class="menuitem login"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M10 17.25V14H3v-4h7V6.75L15.25 12 10 17.25M8 2h9a2 2 0 0 1 2 2v16a2 2 0 0 1-2 2H8a2 2 0 0 1-2-2v-4h2v4h9V4H8v4H6V4a2 2 0 0 1 2-2z"/></svg><span>Log In</span></a></li>
|
||
|
|
<li class="divider" role="separator"></li>
|
||
|
|
|
||
|
|
|
||
|
|
<li class="dropdown-header">
|
||
|
|
<span class="iconify" data-icon="mdi:toolbox"></span> Site Tools </li>
|
||
|
|
|
||
|
|
<li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=recent" title="Recent Changes [r]" rel="nofollow" accesskey="r" class="menuitem recent"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M15 13h1.5v2.82l2.44 1.41-.75 1.3L15 16.69V13m4-5H5v11h4.67c-.43-.91-.67-1.93-.67-3a7 7 0 0 1 7-7c1.07 0 2.09.24 3 .67V8M5 21a2 2 0 0 1-2-2V5c0-1.11.89-2 2-2h1V1h2v2h8V1h2v2h1a2 2 0 0 1 2 2v6.1c1.24 1.26 2 2.99 2 4.9a7 7 0 0 1-7 7c-1.91 0-3.64-.76-4.9-2H5m11-9.85A4.85 4.85 0 0 0 11.15 16c0 2.68 2.17 4.85 4.85 4.85A4.85 4.85 0 0 0 20.85 16c0-2.68-2.17-4.85-4.85-4.85z"/></svg><span>Recent Changes</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=media&ns=syntax%3Aexpansion" title="Media Manager" rel="nofollow" class="menuitem media"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M7 15l4.5-6 3.5 4.5 2.5-3L21 15m1-11h-8l-2-2H6a2 2 0 0 0-2 2v12a2 2 0 0 0 2 2h16a2 2 0 0 0 2-2V6a2 2 0 0 0-2-2M2 6H0v14a2 2 0 0 0 2 2h18v-2H2V6z"/></svg><span>Media Manager</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=index" title="Sitemap [x]" rel="nofollow" accesskey="x" class="menuitem index"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M3 3h6v4H3V3m12 7h6v4h-6v-4m0 7h6v4h-6v-4m-2-4H7v5h6v2H5V9h2v2h6v2z"/></svg><span>Sitemap</span></a></li>
|
||
|
|
<li class="divider" role="separator"></li>
|
||
|
|
|
||
|
|
|
||
|
|
<li class="dropdown-header">
|
||
|
|
<span class="iconify" data-icon="mdi:file-document-outline"></span> Page Tools </li>
|
||
|
|
|
||
|
|
<li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=" title="Show page [v]" rel="nofollow" accesskey="v" class="menuitem show"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M13 9h5.5L13 3.5V9M6 2h8l6 6v12a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V4c0-1.11.89-2 2-2m9 16v-2H6v2h9m3-4v-2H6v2h12z"/></svg><span>Show page</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=revisions" title="Old revisions [o]" rel="nofollow" accesskey="o" class="menuitem revs"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M11 7v5.11l4.71 2.79.79-1.28-4-2.37V7m0-5C8.97 2 5.91 3.92 4.27 6.77L2 4.5V11h6.5L5.75 8.25C6.96 5.73 9.5 4 12.5 4a7.5 7.5 0 0 1 7.5 7.5 7.5 7.5 0 0 1-7.5 7.5c-3.27 0-6.03-2.09-7.06-5h-2.1c1.1 4.03 4.77 7 9.16 7 5.24 0 9.5-4.25 9.5-9.5A9.5 9.5 0 0 0 12.5 2z"/></svg><span>Old revisions</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=backlink" title="Backlinks" rel="nofollow" class="menuitem backlink"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M10.59 13.41c.41.39.41 1.03 0 1.42-.39.39-1.03.39-1.42 0a5.003 5.003 0 0 1 0-7.07l3.54-3.54a5.003 5.003 0 0 1 7.07 0 5.003 5.003 0 0 1 0 7.07l-1.49 1.49c.01-.82-.12-1.64-.4-2.42l.47-.48a2.982 2.982 0 0 0 0-4.24 2.982 2.982 0 0 0-4.24 0l-3.53 3.53a2.982 2.982 0 0 0 0 4.24m2.82-4.24c.39-.39 1.03-.39 1.42 0a5.003 5.003 0 0 1 0 7.07l-3.54 3.54a5.003 5.003 0 0 1-7.07 0 5.003 5.003 0 0 1 0-7.07l1.49-1.49c-.01.82.12 1.64.4 2.43l-.47.47a2.982 2.982 0 0 0 0 4.24 2.982 2.982 0 0 0 4.24 0l3.53-3.53a2.982 2.982 0 0 0 0-4.24.973.973 0 0 1 0-1.42z"/></svg><span>Backlinks</span></a></li><li class="action"><a href="#dokuwiki__top" title="Back to top [t]" rel="nofollow" accesskey="t" class="menuitem top"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8v12z"/></svg><span>Back to top</span></a></li>
|
||
|
|
|
||
|
|
</ul>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
|
||
|
|
</ul>
|
||
|
|
<!-- /tools-menu -->
|
||
|
|
|
||
|
|
<ul class="nav navbar-nav">
|
||
|
|
|
||
|
|
|
||
|
|
<li>
|
||
|
|
<span class="dw__actions dw-action-icon">
|
||
|
|
<a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=register" title="Register" rel="nofollow" class="menuitem register btn btn-success navbar-btn"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M15 14c-2.67 0-8 1.33-8 4v2h16v-2c0-2.67-5.33-4-8-4m-9-4V7H4v3H1v2h3v3h2v-3h3v-2m6 2a4 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 4z"/></svg><span class=""> Register</span></a><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=login&sectok=" title="Log In" rel="nofollow" class="menuitem login btn btn-default navbar-btn"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M10 17.25V14H3v-4h7V6.75L15.25 12 10 17.25M8 2h9a2 2 0 0 1 2 2v16a2 2 0 0 1-2 2H8a2 2 0 0 1-2-2v-4h2v4h9V4H8v4H6V4a2 2 0 0 1 2-2z"/></svg><span class=""> Log In</span></a> </span>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</nav>
|
||
|
|
<!-- navbar -->
|
||
|
|
<div align="center">
|
||
|
|
<script async src="//web.archive.org/web/20220706152308js_/https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
|
||
|
|
<!-- BHORG_BOTTOM -->
|
||
|
|
<ins class="adsbygoogle" style="display:inline-block;width:728px;height:90px" data-ad-client="ca-pub-4658830517838678" data-ad-slot="1603598940"></ins>
|
||
|
|
<script>
|
||
|
|
(adsbygoogle = window.adsbygoogle || []).push({});
|
||
|
|
</script>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</header>
|
||
|
|
|
||
|
|
<a name="dokuwiki__top" id="dokuwiki__top"></a>
|
||
|
|
|
||
|
|
<main role="main" class="dw-container pb-5 dokuwiki container-fluid mx-5">
|
||
|
|
|
||
|
|
<div id="dokuwiki__pageheader">
|
||
|
|
|
||
|
|
|
||
|
|
<!-- breadcrumbs -->
|
||
|
|
<nav id="dw__breadcrumbs" class="small">
|
||
|
|
|
||
|
|
<hr/>
|
||
|
|
|
||
|
|
<div class="dw__youarehere">
|
||
|
|
<ol class="breadcrumb" itemscope itemtype="http://schema.org/BreadcrumbList"><li>You are here</li><li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a href="/web/20220706152308/https://wiki.bash-hackers.org/start" itemprop="item" title="start"><span itemprop="name"><span class="iconify" data-icon="mdi:home"></span></span></a></li><li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a itemprop="item" href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/start" class="wikilink1" title="syntax:start">Syntax</a></li><li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><a itemprop="item" href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/start" class="wikilink1" title="syntax:expansion:start">Syntax: Expansions</a></li><li class="active" itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem"><span itemprop="name"><a itemprop="item" href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst" class="wikilink1" title="syntax:expansion:cmdsubst">Command substitution</a></span></li></ol> </div>
|
||
|
|
|
||
|
|
<div class="dw__breadcrumbs hidden-print">
|
||
|
|
<ol class="breadcrumb"><li>Trace</li> </div>
|
||
|
|
|
||
|
|
<hr/>
|
||
|
|
|
||
|
|
</nav>
|
||
|
|
<!-- /breadcrumbs -->
|
||
|
|
|
||
|
|
<p class="text-right">
|
||
|
|
<span class="pageId ml-1 label label-primary">syntax:expansion:cmdsubst</span> </p>
|
||
|
|
|
||
|
|
<div id="dw__msgarea" class="small">
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="row">
|
||
|
|
|
||
|
|
|
||
|
|
<article id="dokuwiki__content" class="col-sm-12 col-md-12 " itemscope itemtype="http://schema.org/Article" itemref="dw__license">
|
||
|
|
|
||
|
|
|
||
|
|
<!-- page-tools -->
|
||
|
|
<nav id="dw__pagetools" class="hidden-print">
|
||
|
|
<div class="tools panel panel-default">
|
||
|
|
<ul class="nav nav-stacked nav-pills text-muted">
|
||
|
|
<li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=" title="Show page [v]" rel="nofollow" accesskey="v" class="menuitem show"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M13 9h5.5L13 3.5V9M6 2h8l6 6v12a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V4c0-1.11.89-2 2-2m9 16v-2H6v2h9m3-4v-2H6v2h12z"/></svg><span>Show page</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=revisions" title="Old revisions [o]" rel="nofollow" accesskey="o" class="menuitem revs"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M11 7v5.11l4.71 2.79.79-1.28-4-2.37V7m0-5C8.97 2 5.91 3.92 4.27 6.77L2 4.5V11h6.5L5.75 8.25C6.96 5.73 9.5 4 12.5 4a7.5 7.5 0 0 1 7.5 7.5 7.5 7.5 0 0 1-7.5 7.5c-3.27 0-6.03-2.09-7.06-5h-2.1c1.1 4.03 4.77 7 9.16 7 5.24 0 9.5-4.25 9.5-9.5A9.5 9.5 0 0 0 12.5 2z"/></svg><span>Old revisions</span></a></li><li class="action"><a href="/web/20220706152308/https://wiki.bash-hackers.org/syntax/expansion/cmdsubst?do=backlink" title="Backlinks" rel="nofollow" class="menuitem backlink"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M10.59 13.41c.41.39.41 1.03 0 1.42-.39.39-1.03.39-1.42 0a5.003 5.003 0 0 1 0-7.07l3.54-3.54a5.003 5.003 0 0 1 7.07 0 5.003 5.003 0 0 1 0 7.07l-1.49 1.49c.01-.82-.12-1.64-.4-2.42l.47-.48a2.982 2.982 0 0 0 0-4.24 2.982 2.982 0 0 0-4.24 0l-3.53 3.53a2.982 2.982 0 0 0 0 4.24m2.82-4.24c.39-.39 1.03-.39 1.42 0a5.003 5.003 0 0 1 0 7.07l-3.54 3.54a5.003 5.003 0 0 1-7.07 0 5.003 5.003 0 0 1 0-7.07l1.49-1.49c-.01.82.12 1.64.4 2.43l-.47.47a2.982 2.982 0 0 0 0 4.24 2.982 2.982 0 0 0 4.24 0l3.53-3.53a2.982 2.982 0 0 0 0-4.24.973.973 0 0 1 0-1.42z"/></svg><span>Backlinks</span></a></li><li class="action"><a href="#dokuwiki__top" title="Back to top [t]" rel="nofollow" accesskey="t" class="menuitem top"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8v12z"/></svg><span>Back to top</span></a></li> </ul>
|
||
|
|
</div>
|
||
|
|
</nav>
|
||
|
|
<!-- /page-tools -->
|
||
|
|
|
||
|
|
<div class="panel panel-default px-3 py-2" itemprop="articleBody">
|
||
|
|
<div class="page panel-body">
|
||
|
|
|
||
|
|
|
||
|
|
<div class="dw-content-page "><!-- content --><div class="dw-content"><p>
|
||
|
|
This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
|
||
|
|
</p>
|
||
|
|
<div class="editBox" role="application">
|
||
|
|
|
||
|
|
<div class="toolbar group">
|
||
|
|
<div id="draft__status" class="draft__status"></div>
|
||
|
|
<div id="tool__bar" class="tool__bar"></div>
|
||
|
|
</div>
|
||
|
|
<form id="dw__editform" method="post" action="" accept-charset="utf-8" class=" form-inline"><div class="no">
|
||
|
|
<input type="hidden" name="sectok" value=""/><input type="hidden" name="id" value="syntax:expansion:cmdsubst"/><input type="hidden" name="rev" value="0"/><input type="hidden" name="date" value="0"/><input type="hidden" name="prefix" value="."/><input type="hidden" name="suffix" value=""/><input type="hidden" name="changecheck" value="72a1f925a8918c8a22ad2aa2fbabaeac"/><input type="hidden" name="target" value="section"/><textarea name="wikitext" id="wiki__text" dir="auto" class="edit form-control" cols="80" rows="10" tabindex="1" readonly="readonly">
|
||
|
|
====== Command substitution ======
|
||
|
|
|
||
|
|
{{keywords>bash shell scripting expansion substitution text variable output execute stdout save result return value}}
|
||
|
|
|
||
|
|
<code>
|
||
|
|
$( <COMMANDS> )
|
||
|
|
|
||
|
|
` <COMMANDS> `
|
||
|
|
</code>
|
||
|
|
|
||
|
|
The command substitution expands to the output of commands. These commands are executed in a subshell, and their ''stdout'' data is what the substitution syntax expands to.
|
||
|
|
|
||
|
|
All **trailing** newlines are removed (below is an example for a workaround).
|
||
|
|
|
||
|
|
In later steps, **if not quoted**, the results undergo [[syntax:expansion:wordsplit | word splitting]] and [[syntax:expansion:globs | pathname expansion]]. You have to remember that, because the word splitting will also remove embedded newlines and other ''IFS'' characters and break the results up into several words. Also you'll probably get unexpected pathname matches. **If you need the literal results, quote the command substitution!**
|
||
|
|
|
||
|
|
The second form ''`COMMAND`'' is more or less obsolete for Bash, since it has some trouble with nesting ("inner" backticks need to be escaped) and escaping characters. Use ''$(COMMAND)'', it's also POSIX!
|
||
|
|
|
||
|
|
When you [[syntax:ccmd:grouping_subshell | call an explicit subshell]] ''(COMMAND)'' inside the command substitution ''$()'', then take care, this way is **wrong**:
|
||
|
|
<code>
|
||
|
|
$((COMMAND))
|
||
|
|
</code>
|
||
|
|
Why? because it collides with the syntax for [[syntax:expansion:arith | arithmetic expansion]]. You need to separate the command substitution from the inner ''(COMMAND)'':
|
||
|
|
<code>
|
||
|
|
$( (COMMAND) )
|
||
|
|
</code>
|
||
|
|
|
||
|
|
===== Specialities =====
|
||
|
|
|
||
|
|
When the inner command is only an input redirection, and nothing else, for example
|
||
|
|
<code>
|
||
|
|
$( <FILE )
|
||
|
|
# or
|
||
|
|
` <FILE `
|
||
|
|
</code>
|
||
|
|
then Bash attempts to read the given file and act just if the given command was ''cat FILE''.
|
||
|
|
|
||
|
|
|
||
|
|
===== A closer look at the two forms =====
|
||
|
|
|
||
|
|
In general you really should only use the form ''$()'', it's escaping-neutral, it's nestable, it's also POSIX. But take a look at the following code snips to decide yourself which form you need under specific circumstances:
|
||
|
|
|
||
|
|
**__Nesting__**
|
||
|
|
|
||
|
|
Backtick form ''`...`'' is not directly nestable. You will have to escape the "inner" backticks. Also, the deeper you go, the more escape characters you need. Ugly.
|
||
|
|
|
||
|
|
<code>
|
||
|
|
echo `echo `ls`` # INCORRECT
|
||
|
|
echo `echo \`ls\`` # CORRECT
|
||
|
|
echo $(echo $(ls)) # CORRECT
|
||
|
|
</code>
|
||
|
|
|
||
|
|
**__Parsing__**
|
||
|
|
|
||
|
|
All is based on the fact that the backquote-form is simple character substitution, while every ''$()''-construct opens an own, subsequent parsing step. Everything inside ''$()'' is interpreted as if written normal on a commandline. No special escaping of **nothing** is needed:
|
||
|
|
|
||
|
|
<code>
|
||
|
|
echo "$(echo "$(ls)")" # nested double-quotes - no problem
|
||
|
|
</code>
|
||
|
|
|
||
|
|
**__Constructs you should avoid__**
|
||
|
|
|
||
|
|
It's not all shiny with ''$()'', at least for my current Bash (''3.1.17(1)-release''. :!: __**Update:** Fixed since ''3.2-beta'' together with a misinterpretion of '))' being recognized as arithmetic expansion [by redduck666]__). This command seems to incorrectly close the substitution step and echo prints "ls" and ")":
|
||
|
|
<code>
|
||
|
|
echo $(
|
||
|
|
# some comment ending with a )
|
||
|
|
ls
|
||
|
|
)
|
||
|
|
</code>
|
||
|
|
|
||
|
|
It seems that every closing ")" confuses this construct. Also a (very uncommon ;-)) construct like:
|
||
|
|
<code>
|
||
|
|
echo $(read VAR; case "$var" in foo) blah ;; esac) # spits out some error, when it sees the ";;"
|
||
|
|
|
||
|
|
# fixes it:
|
||
|
|
echo $(read VAR; case "$var" in (foo) blah ;; esac) # will work, but just let it be, please ;-)
|
||
|
|
</code>
|
||
|
|
|
||
|
|
**__Conclusion:__**
|
||
|
|
|
||
|
|
In general, the ''$()'' should be the preferred method:
|
||
|
|
* it's clean syntax
|
||
|
|
* it's intuitive syntax
|
||
|
|
* it's more readable
|
||
|
|
* it's nestable
|
||
|
|
* its inner parsing is separate
|
||
|
|
|
||
|
|
===== Examples =====
|
||
|
|
|
||
|
|
**To get the date:**
|
||
|
|
<code>
|
||
|
|
DATE="$(date)"
|
||
|
|
</code>
|
||
|
|
|
||
|
|
**To copy a file and get ''cp'' error output:**
|
||
|
|
<code>
|
||
|
|
COPY_OUTPUT="$(cp file.txt /some/where 2>&1)"
|
||
|
|
</code>
|
||
|
|
Attention: Here, you need to redirect ''cp'' ''STDERR'' to its ''STDOUT'' target, because command substitution only catches ''STDOUT''!
|
||
|
|
|
||
|
|
**Catch stdout and preserve trailing newlines:**
|
||
|
|
<code>
|
||
|
|
var=$(echo -n $'\n'); echo -n "$var"; # $var == ""
|
||
|
|
var=$(echo -n $'\n'; echo -n x); var="${var%x}"; echo -n "$var" # $var == "\n"
|
||
|
|
</code>
|
||
|
|
|
||
|
|
This adds "x" to the output, which prevents the trailing newlines of the previous commands' output from being deleted by $().
|
||
|
|
|
||
|
|
By removing this "x" later on, we are left with the previous commands' output with its trailing newlines.
|
||
|
|
|
||
|
|
===== See also =====
|
||
|
|
* Internal: [[syntax:expansion:intro | Introduction to expansion and substitution]]
|
||
|
|
* Internal: [[scripting:obsolete | Obsolete and deprecated syntax]]
|
||
|
|
</textarea>
|
||
|
|
<div id="wiki__editbar" class="editBar">
|
||
|
|
<div id="size__ctl">
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div></form>
|
||
|
|
</div>
|
||
|
|
</div><!-- /content --></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="small text-right">
|
||
|
|
|
||
|
|
<span class="docInfo">
|
||
|
|
<ul class="list-inline"><li><span class="iconify text-muted" data-icon="mdi:file-document-outline"></span> <span title="syntax/expansion/cmdsubst.txt">syntax/expansion/cmdsubst.txt</span></li><li><span class="iconify text-muted" data-icon="mdi:calendar"></span> Last modified: <span title="2010/09/09 16:45">2010/09/09 16:45</span></li><li>(external edit)</li></ul> </span>
|
||
|
|
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</article>
|
||
|
|
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</main>
|
||
|
|
|
||
|
|
<footer id="dw__footer" class="dw-container py-5 dokuwiki container-fluid">
|
||
|
|
<hr/>
|
||
|
|
<div align="center">
|
||
|
|
<h3><a target="_blank" href="http://web.archive.org/web/20220706152308/http://www.performing-databases.com/">This site is supported by Performing Databases - your experts for database administration</a></h3>
|
||
|
|
</div>
|
||
|
|
<hr/>
|
||
|
|
<div align="center">
|
||
|
|
<script async src="//web.archive.org/web/20220706152308js_/https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
|
||
|
|
<!-- BHORG_BOTTOM -->
|
||
|
|
<ins class="adsbygoogle" style="display:inline-block;width:728px;height:90px" data-ad-client="ca-pub-4658830517838678" data-ad-slot="1603598940"></ins>
|
||
|
|
<script>
|
||
|
|
(adsbygoogle = window.adsbygoogle || []).push({});
|
||
|
|
</script>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<!-- footer -->
|
||
|
|
<div class="dw-container small container-fluid mx-5">
|
||
|
|
|
||
|
|
|
||
|
|
<div class="footer-dw-title">
|
||
|
|
<div class="media">
|
||
|
|
<div class="media-left">
|
||
|
|
<img src="/web/20220706152308im_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/images/logo.png" alt="Bash Hackers Wiki" class="media-object" style="height:32px"/>
|
||
|
|
</div>
|
||
|
|
<div class="media-body">
|
||
|
|
<div class="row">
|
||
|
|
<div class="col-sm-2">
|
||
|
|
<h4 class="media-heading">Bash Hackers Wiki</h4>
|
||
|
|
<p>
|
||
|
|
</p>
|
||
|
|
</div>
|
||
|
|
<div class="col-sm-10">
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="footer-license row">
|
||
|
|
<hr/>
|
||
|
|
<div id="dw__license" class="col-sm-6">
|
||
|
|
<p>
|
||
|
|
<a href="http://web.archive.org/web/20220706152308/http://www.gnu.org/licenses/fdl-1.3.html" title="GNU Free Documentation License 1.3" target="" itemscope itemtype="http://schema.org/CreativeWork" itemprop="license" rel="license" class="license"><img src="/web/20220706152308im_/https://wiki.bash-hackers.org/lib/tpl/bootstrap3/images/license/gnufdl.png" width="24" height="24" alt="gnufdl"/> </a> </p>
|
||
|
|
<p class="small">
|
||
|
|
Except where otherwise noted, content on this wiki is licensed under the following license:<br/><a href="http://web.archive.org/web/20220706152308/http://www.gnu.org/licenses/fdl-1.3.html" title="GNU Free Documentation License 1.3" target="" itemscope itemtype="http://schema.org/CreativeWork" itemprop="license" rel="license" class="license">GNU Free Documentation License 1.3</a> </p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<div class="col-sm-6">
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
<!-- /footer -->
|
||
|
|
</footer>
|
||
|
|
|
||
|
|
<a href="#dokuwiki__top" class="back-to-top hidden-print btn btn-default" title="skip to content" accesskey="t">
|
||
|
|
<span class="iconify" data-icon="mdi:chevron-up"></span> </a>
|
||
|
|
|
||
|
|
<div id="screen__mode"> <span class="visible-xs-block"></span>
|
||
|
|
<span class="visible-sm-block"></span>
|
||
|
|
<span class="visible-md-block"></span>
|
||
|
|
<span class="visible-lg-block"></span>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<img src="/web/20220706152308im_/https://wiki.bash-hackers.org/lib/exe/indexer.php?id=syntax%3Aexpansion%3Acmdsubst&1657120990" width="2" height="1" alt=""/>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
<!--
|
||
|
|
FILE ARCHIVED ON 15:23:08 Jul 06, 2022 AND RETRIEVED FROM THE
|
||
|
|
INTERNET ARCHIVE ON 11:36:43 Apr 14, 2023.
|
||
|
|
JAVASCRIPT APPENDED BY WAYBACK MACHINE, COPYRIGHT INTERNET ARCHIVE.
|
||
|
|
|
||
|
|
ALL OTHER CONTENT MAY ALSO BE PROTECTED BY COPYRIGHT (17 U.S.C.
|
||
|
|
SECTION 108(a)(3)).
|
||
|
|
-->
|
||
|
|
<!--
|
||
|
|
playback timings (ms):
|
||
|
|
captures_list: 100.408
|
||
|
|
exclusion.robots: 0.139
|
||
|
|
exclusion.robots.policy: 0.128
|
||
|
|
cdx.remote: 0.066
|
||
|
|
esindex: 0.007
|
||
|
|
LoadShardBlock: 69.048 (3)
|
||
|
|
PetaboxLoader3.datanode: 72.284 (4)
|
||
|
|
load_resource: 231.349
|
||
|
|
PetaboxLoader3.resolve: 188.834
|
||
|
|
-->
|