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| author | neodarz <neodarz@neodarz.net> | 2017-04-28 19:05:18 +0200 |
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| committer | neodarz <neodarz@neodarz.net> | 2017-04-28 19:05:18 +0200 |
| commit | cdabe7a75ea14f14ca8d4cd3bf9ac36cb1817531 (patch) | |
| tree | a3a9557d77f376394bb8e49fc48dcdef556ecb38 /build/blog/2015-05-19-bash-the-special-slash-character-in-filename-expansion.html | |
| parent | d08bc695f396f8e2d7fc96de7efe61818c7c9a15 (diff) | |
| download | my_new_personal_website-cdabe7a75ea14f14ca8d4cd3bf9ac36cb1817531.tar.xz my_new_personal_website-cdabe7a75ea14f14ca8d4cd3bf9ac36cb1817531.zip | |
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diff --git a/build/blog/2015-05-19-bash-the-special-slash-character-in-filename-expansion.html b/build/blog/2015-05-19-bash-the-special-slash-character-in-filename-expansion.html deleted file mode 100644 index 580272ae..00000000 --- a/build/blog/2015-05-19-bash-the-special-slash-character-in-filename-expansion.html +++ /dev/null @@ -1,69 +0,0 @@ -<!DOCTYPE html> -<html> -<head> -<meta charset="utf-8"/> -<meta content="pandoc" name="generator"/> -<meta content="Zhiming Wang" name="author"/> -<meta content="2015-05-19T18:33:51-07:00" name="date"/> -<title>Bash: the special slash character in filename expansion</title> -<link href="/img/apple-touch-icon-152.png" rel="apple-touch-icon-precomposed"/> -<meta content="#FFFFFF" name="msapplication-TileColor"/> -<meta content="/img/favicon-144.png" name="msapplication-TileImage"/> -<meta content="width=device-width, initial-scale=1" name="viewport"/> -<link href="/css/normalize.min.css" media="all" rel="stylesheet" type="text/css"/> -<link href="/css/theme.css" media="all" rel="stylesheet" type="text/css"/> -<link href="/css/highlight.css" media="all" rel="stylesheet" type="text/css"/> -</head> -<body> -<div id="archival-notice">This blog has been archived.<br/>Visit my home page at <a href="https://zhimingwang.org">zhimingwang.org</a>.</div> -<nav class="nav"> -<a class="nav-icon" href="/" title="Home"><!--blog icon--></a> -<a class="nav-title" href="/"><!--blog title--></a> -<a class="nav-author" href="https://github.com/zmwangx" target="_blank"><!--blog author--></a> -</nav> -<article class="content"> -<header class="article-header"> -<h1 class="article-title">Bash: the special slash character in filename expansion</h1> -<div class="article-metadata"> -<time class="article-timestamp" datetime="2015-05-19T18:33:51-07:00">May 19, 2015</time> -</div> -</header> -<p>It is well-known and common sense that the slash character (<code>/</code>) serves a special role in Bash filename expansion. For instance, the asterisk <code>*</code> certainly won't match <code>/</code> or <code>.</code> when used in filename expansion; otherwise, a standalone <code>*</code> would match everything in the filesystem.</p> -<p>However, it is less clear how a literal slash character<a class="footnoteRef" href="#fn1" id="fnref1"><sup>1</sup></a> is treated in extended glob patterns. Naively one would expect it to just match a literal slash, but the real situtation is more complicated than that. Consider the following examples:</p> -<div class="sourceCode"><pre class="sourceCode bash"><code class="sourceCode bash"><span class="ex">bash-4.3</span>$ shopt -s extglob nullglob -<span class="ex">bash-4.3</span>$ echo /usr/@(bin<span class="kw">|</span><span class="ex">lib</span>) -<span class="ex">/usr/bin</span> /usr/lib -<span class="ex">bash-4.3</span>$ echo /usr@(/bin<span class="kw">|</span><span class="ex">/lib</span>) - -<span class="ex">bash-4.3</span>$ [[ /usr/bin == /usr@(/bin<span class="kw">|</span><span class="ex">/lib</span>) ]] <span class="kw">&&</span> <span class="bu">echo</span> matching -<span class="ex">matching</span></code></pre></div> -<p>As seen from this example, patterns with slash simply doesn't work (in filename expansion) when placed in an extended glob pattern list, and there's no error whatsoever. I looked up the <a href="https://www.gnu.org/software/bash/manual/html_node/Pattern-Matching.html#Pattern-Matching">Bash Reference Manual</a> and the <a href="http://mywiki.wooledge.org/BashGuide/Patterns">Bash Guide</a> but neither mentioned this behavior. One might need to delve into the source code to say for sure what exactly is going on.</p> -<p>In comparison, Zsh and its <a href="http://zsh.sourceforge.net/Doc/Release/Expansion.html#Filename-Generation">docs</a> are much more up front about this issue:</p> -<blockquote> -<p>Note that grouping cannot extend over multiple directories: it is an error to have a â/â within a group (this only applies for patterns used in filename generation). ...</p> -</blockquote> -<p>And when we run equivalent code in Zsh:</p> -<div class="sourceCode"><pre class="sourceCode zsh"><code class="sourceCode zsh">zsh-5.0.5$ <span class="kw">setopt</span> NULL_GLOB -zsh-5.0.5$ <span class="kw">echo</span> /usr/<span class="kw">(</span>bin<span class="kw">|</span>lib<span class="kw">)</span> -/usr/bin /usr/lib -zsh-5.0.5$ <span class="kw">echo</span> /usr<span class="kw">(</span>/bin<span class="kw">|</span>/lib<span class="kw">)</span> -zsh: bad pattern: /usr<span class="kw">(</span>/bin<span class="kw">|</span>/lib<span class="kw">)</span> -zsh-5.0.5$<span class="kw"> [[</span> /usr/bin <span class="ot">==</span> /usr(/bin|/lib)<span class="kw"> ]]</span> <span class="kw">&&</span> <span class="kw">echo</span> matching -matching</code></pre></div> -<p>The lesson? Be careful not to use a pattern like <code>@(path1|path2|path3)</code> in Bash when the paths are absolute, or relative but contain the slash. Unlike Zsh, Bash just silently fails on a pattern like this, which is rather dangerous in scripts.</p> -<div class="footnotes"> -<hr/> -<ol> -<li id="fn1"><p>Here, "a literal slash character" also applies to one that comes from tilde expansion, parameter expansion or command substitution, since they are performed before filename expansion in Bash.<a class="footnotes-backlink" href="#fnref1">âŠī¸</a></p></li> -</ol> -</div> -</article> -<hr class="content-separator"/> -<footer class="footer"> -<span class="rfooter"> -<a class="rss-icon" href="/rss.xml" target="_blank" title="RSS feed"><!--RSS feed icon--></a><a class="atom-icon" href="/atom.xml" target="_blank" title="Atom feed"><!--Atom feed icon--></a><a class="cc-icon" href="https://creativecommons.org/licenses/by/4.0/" target="_blank" title="Released under the Creative Commons Attribution 4.0 International license."><!--CC icon--></a> -<a href="https://github.com/zmwangx" target="_blank">Zhiming Wang</a> -</span> -</footer> -</body> -</html> |