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| author | garhve <git@garhve.com> | 2023-02-14 18:40:10 +0800 |
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| committer | garhve <git@garhve.com> | 2023-02-14 18:40:10 +0800 |
| commit | 4d12e92153c463bd5fecbc9606a5489601f57ee6 (patch) | |
| tree | 84990b20afd1d1c4d7bec1f681b5c3236eef1f4b /posts/6/index.html | |
| parent | 734f042c9d99e0110d5e4cf8f2994a5ce27385d1 (diff) | |
change back to hugo
Diffstat (limited to 'posts/6/index.html')
| -rw-r--r-- | posts/6/index.html | 361 |
1 files changed, 361 insertions, 0 deletions
diff --git a/posts/6/index.html b/posts/6/index.html new file mode 100644 index 0000000..ecb751a --- /dev/null +++ b/posts/6/index.html @@ -0,0 +1,361 @@ +<!DOCTYPE html> +<html lang="en"> +<head> + <meta charset="utf-8" /> + <meta name="generator" content="Hugo 0.108.0"> + + <meta http-equiv="X-UA-Compatible" content="IE=edge" /> + <meta name="viewport" content="width=device-width, initial-scale=1" /> + <meta name="author" content="garhve" /> + <meta property="og:url" content="https://blog.garhve.com/posts/6/" /> + <link rel="canonical" href="https://blog.garhve.com/posts/6/" /><link rel="apple-touch-icon" href="https://assets.garhve.com/pictures/assets/images/favicon/favicon.ico" /> + <link rel="icon" href="https://assets.garhve.com/pictures/assets/images/favicon/favicon.ico" /> + <link rel="shortcut" href="https://assets.garhve.com/pictures/assets/images/favicon/favicon.ico" /><link rel="alternate" type="application/atom+xml" href="https://blog.garhve.comindex.xml" title="blog | garhve's hub"> + + <script type="application/ld+json"> + { + "@context" : "http://schema.org", + "@type" : "BlogPosting", + "mainEntityOfPage": { + "@type": "WebPage", + "@id": "https:\/\/blog.garhve.com" + }, + "articleSection" : "posts", + "name" : "Mess with Bash(2)", + "headline" : "Mess with Bash(2)", + "description" : "More info is in this tutorial\nall value expansions (ie. all syntax with a $ prefix) can only expand inside quoted arguments if the argument was double-quoted . Single quotes will turn the dollar-syntax into literal characters, causing bash to output the dollar rather than expand its value in-place!\n\u0026ldquo;Value expansions ($...) must always be double-quoted.\u0026rdquo;\nNever leave a value expansion unquoted.\nRedirection File Redirection 0 is standard input, 1 is standard output, 2 is standard error", + "inLanguage" : "en-US", + "author" : "garhve", + "creator" : "garhve", + "publisher": "garhve", + "accountablePerson" : "garhve", + "copyrightHolder" : "garhve", + "copyrightYear" : "2022", + "datePublished": "2022-09-29 09:43:02 \u002b0800 CST", + "dateModified" : "2022-09-29 09:43:02 \u002b0800 CST", + "url" : "https:\/\/blog.garhve.com\/posts\/6\/", + "keywords" : [ ] + } +</script> +<title>Mess with Bash(2)</title> + <meta property="og:title" content="Mess with Bash(2)" /> + <meta property="og:type" content="article" /> + <meta property="og:description" content="More info is in this tutorial +all value expansions (ie. all syntax with a $ prefix) can only expand inside quoted arguments if the argument was double-quoted . Single quotes will turn the dollar-syntax into literal characters, causing bash to output the dollar rather than expand its value in-place! +&ldquo;Value expansions ($...) must always be double-quoted.&rdquo; +Never leave a value expansion unquoted. +Redirection File Redirection 0 is standard input, 1 is standard output, 2 is standard error" /> + <meta name="description" content="More info is in this tutorial +all value expansions (ie. all syntax with a $ prefix) can only expand inside quoted arguments if the argument was double-quoted . Single quotes will turn the dollar-syntax into literal characters, causing bash to output the dollar rather than expand its value in-place! +&ldquo;Value expansions ($...) must always be double-quoted.&rdquo; +Never leave a value expansion unquoted. +Redirection File Redirection 0 is standard input, 1 is standard output, 2 is standard error" /> + <meta property="og:locale" content="en-us" /><meta property="og:image" content="https://assets.garhve.com/pictures/assets/images/favicon/favicon.ico" /> + + + + + <style>@font-face{font-family:huanzi;src:url(/fonts/huanzi.woff2)format('woff2')}@font-face{font-family:fira code;src:url(/fonts/FiraCode-Regular.woff2)format('woff2')}body{font-family:bree serif,huanzi,sans-serif;-webkit-font-smoothing:antialiased;margin:0 20px}article{max-width:800px;margin-left:auto;margin-right:auto}a{color:#000;text-decoration:none}a:hover{font-weight:600;text-decoration:underline}.post-ads{margin:50px 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+ + + + + <link href="/index.xml" rel="alternate" type="application/rss+xml" + title="blog | garhve's hub"> + + <link rel="preconnect" href="https://fonts.gstatic.com"> + <link href="https://fonts.googleapis.com/css?family=Bree+Serif|Bungee+Shade" rel="stylesheet"> + + + +</head> + + +<body> + <article class="post English" id="article"> + <div class="row"> + <div class="col-xs-12"> + <div class="site-header"> + +<header> + <div class="header-title"> + <a href="/" + >Garhve</a + > + </div> + <div class="header-subtitle"></div> +</header> +<div class="row end-md center-xs header-items"> +</div> +<div class="row end-xs"> + + <div class="lang-switch col-xs-3 col-xs-offset-9"> + <a href="/cn/">Chinese</a> + </div> + +</div> +<div class="header-line"></div> + + </div> + <header class="post-header"> + <h1 class="post-title">Mess with Bash(2)</h1> + + <div class="row post-desc"> + <div class="col-xs-6"> + + <time class="post-date" datetime="2022-09-29 09:43:02 CST"> + 29 Sep 2022 + </time> + + </div> + <div class="col-xs-6"> + + <div class="post-author"> + <a target="_blank" href="https://garhve.com">@garhve</a> + </div> + + </div> + </div> + + </header> + + <div class="post-content markdown-body"> + + <blockquote> +<p>More info is in this <a href="https://https://guide.bash.academy">tutorial</a></p> +</blockquote> +<blockquote> +<p>all value expansions (ie. all syntax with a <code>$</code> prefix) can only expand inside quoted arguments if the argument was <em>double-quoted</em> . Single quotes will turn the dollar-syntax into literal characters, causing bash to output the dollar rather than expand its value in-place!</p> +</blockquote> +<p><em>“Value expansions (<code>$...</code>) must <strong>always</strong> be double-quoted.”</em></p> +<p><em>Never leave a value expansion unquoted.</em></p> +<h2 id="redirection">Redirection</h2> +<h3 id="file-redirection">File Redirection</h3> +<p><strong>0 is standard input, 1 is standard output, 2 is standard error</strong></p> +<p><code>[x] > file, [x] < file</code></p> +<p>Make <em><strong>File descriptor</strong></em>(FD) <code>x</code> write to / read from file.</p> +<blockquote> +<p><code>echo hello > ~/World</code></p> +<p><code>read line < ~/Word</code></p> +<p><code>rm file 2>/dev/null</code></p> +</blockquote> +<h3 id="file-descriptor-copying">File Descriptor copying</h3> +<p><code>[x] >& y, [x] <& y</code></p> +<p>make FD <code>x</code> write to / read from FD <code>y</code>’s stream</p> +<blockquote> +<p>the connection to the stream used by FD <code>y</code> is copied to FD <code>x</code></p> +<p><code>curl cip.cc > result 2>&1</code></p> +<p><code>ping localhost > result 2>&1</code></p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># exec can be used to change the file descriptors of bash itself,</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># and if you use an x that doesn't yet exist,</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># bash will create a new file descriptor ("plug") for you with that number.</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># - in command is to close new FD 3 we'd created before.</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># >&- is to close FD 1, <&- is to close FD0</span> +</span></span><span style="display:flex;"><span>exec 3>&1 >mylog; echo moo; exec 1>&3 3>&- +</span></span></code></pre></div></blockquote> +<h3 id="appending-file-redirection">Appending file redirection</h3> +<p><code>[x] >> file</code></p> +<p>make FD <code>x</code> append to end of the file</p> +<blockquote> +<p>A stream to <code>file</code> is opened for writing in append mode and is connected to file descriptor <code>x</code>. The regular file redirection operator <code>></code> empties the file’s contents when it opens the file so that only your bytes will be in the file.</p> +<p><code>echo hello >> ~/world</code></p> +<p><code>echo world >> ~/world</code></p> +</blockquote> +<h3 id="redirecting-standard-output-and-standard-error">Redirecting standard output and standard error</h3> +<p><code>&>file</code></p> +<p>Make both FD 1 (standard output) and FD 2 (standard error) write to file</p> +<blockquote> +<p>This is a convenience operator which does the same thing as <code>>file 2>&1</code> but is more concise. Again, you can append rather than truncate by doubling the arrow: <code>&>>file</code></p> +<p><code>ping localhost &>result</code></p> +</blockquote> +<h3 id="here-documents">Here documents</h3> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"><<delimiter +</span></span></span><span style="display:flex;"><span><span style="font-style:italic"> Here document +</span></span></span><span style="display:flex;"><span><span style="font-style:italic">delimiter</span> +</span></span></code></pre></div><p>Make FD 0 read from the string between <code>delimiter</code>s</p> +<blockquote> +<p>Here-Documents are great for reading blocks of text to command line.</p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>cat <span style="font-style:italic"><< EOF +</span></span></span><span style="display:flex;"><span><span style="font-style:italic">this is within here document +</span></span></span><span style="display:flex;"><span><span style="font-style:italic">I can write as many lines as I like +</span></span></span><span style="display:flex;"><span><span style="font-style:italic">and terminate with line of demiliter only +</span></span></span><span style="display:flex;"><span><span style="font-style:italic">EOF</span> //end of heredoc +</span></span></code></pre></div></blockquote> +<h3 id="here-strings">Here strings</h3> +<p><code><<< string</code></p> +<p>Make FD 0 read from the <code>string</code></p> +<blockquote> +<p>Here strings are very similar to here documents but more concise. They are generally preferred over here documents.</p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>cat <<< <span style="font-style:italic">"This, +</span></span></span><span style="display:flex;"><span><span style="font-style:italic">is the here strings. tab will also be read."</span> +</span></span></code></pre></div></blockquote> +<h3 id="moving-file-decipher">Moving file decipher</h3> +<p><code>[x]>&y-, [x]<&y-</code></p> +<p>Replace FD <code>x</code> with FD <code>y</code> and close FD <code>y</code></p> +<blockquote> +<p>Easy way of <code>[x]>&y, y>&-</code></p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># 3>&1-: copy FD 1 to FD 3 and close FD 1.</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># >&3-: copy FD 3 to FD 1 and close FD 3.</span> +</span></span><span style="display:flex;"><span>exec 3>&1- >mylog; echo moo; exec >&3- +</span></span></code></pre></div></blockquote> +<h3 id="reading-and-writing-with-file-descriptor">Reading and writing with file descriptor</h3> +<p><code>[x] <> file</code></p> +<p>Open FD <code>x</code> for both reading and writing to <code>file</code></p> +<blockquote> +<p>The file descriptor at x is opened with a stream to the file that can be used for writing as well as reading bytes. Usually you’ll use two file descriptors for this. <strong>One of the rare cases where this is useful is when setting up a stream with a read/write device such as a network socket</strong>.</p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>exec 5<>aFile +</span></span><span style="display:flex;"><span>cat >&5 <span style="font-style:italic">"Hello world"</span> <span style="font-style:italic"># make FD 1 write to where FD 5 currently writing, copy file descriptor FD 5 to FD 1</span> +</span></span><span style="display:flex;"><span>cat <&5 <span style="font-style:italic"># make FD 0 read from where FD 5 currently reading, copy file descriptor FD 5 to FD 0, then cat will send content to FD 1</span> +</span></span></code></pre></div></blockquote> +<p>Exercise</p> +<blockquote> +<p>Q: fix <code>exec 3>&2 2>log; echo 'Hello!'; exec 2>&3</code> so that the message is properly saved into the <code>log</code> file and such that FD 3 is properly closed afterwards:</p> +<p>A:</p> +<ol> +<li><code>exec 3>&1- 3>log; echo 'Hello!'; exec 1>&3-</code></li> +<li><code>exec 3>&1 1>&- 3>log; echo 'Hello!'; exec 1>&3 3>&-</code></li> +</ol> +</blockquote> +<h2 id="expansion">Expansion</h2> +<h3 id="pathname-expansion">pathname expansion</h3> +<ol> +<li> +<p>pattern expansion is performed by bash before command even execute</p> +<blockquote> +<p><code>file *</code> will show info about all file in current directory. <code>*</code> will expand to content before <code>file</code> execute.</p> +</blockquote> +</li> +<li> +<p>A <em>glob</em> is the name of the type of pattern supported by the bash shell.</p> +<blockquote> +<p>basic glob name supported by bash<img src="https://assets.garhve.com/pictures/screenshots/2022/10/1665123982.png" alt="explanation"></p> +<p><img src="https://assets.garhve.com/pictures/screenshots/2022/10/1665133964.png" alt="example"></p> +<p><strong>Those glob will only affect current directory, explicit expression is required to working on other directory.</strong> <code>ls /sub/*</code></p> +</blockquote> +</li> +<li> +<p>extended glob can be enable to get more powerful but also easy confusing feature of bash</p> +<blockquote> +<p>bash: <code>shopt -s extglob</code> +zsh. : <code>setopt extendedglob</code> +<img src="https://assets.garhve.com/pictures/screenshots/2022/10/1665134156.png" alt="explanation"></p> +<p><img src="https://assets.garhve.com/pictures/screenshots/2022/10/1665134205.png" alt="!(my)* get expand because of * is outside !(), which makes it expland another whole pathname"></p> +</blockquote> +</li> +</ol> +<h3 id="command-substitution">Command Substitution</h3> +<p>we can expansion commands within commands, but must use double-quote <code>""</code> instead of <code>''</code></p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># this will output contents in hello.h to screen</span> +</span></span><span style="display:flex;"><span>cat hello.h +</span></span><span style="display:flex;"><span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># this will expand `cat hello.h` to real contents in </span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># file hello.h and concatenate to previous sentence</span> +</span></span><span style="display:flex;"><span>echo <span style="font-style:italic">"file hello.h contains contents of </span><span style="font-weight:bold">$(</span>cat hello.h<span style="font-weight:bold">)</span><span style="font-style:italic">"</span> +</span></span><span style="display:flex;"><span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># this will output 'file hello.h contains contents of $(cat hello.h)'</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># without expand command in $()</span> +</span></span><span style="display:flex;"><span>echo <span style="font-style:italic">'file hello.h contains contents of $(cat hello.h)'</span> +</span></span></code></pre></div><p>In command, <code>$()</code> is called <em>value expansion</em>, it consists of value-expansion prefix <code>$</code> and subshell <code>(...)</code>. A subshell is essentially a small new bash process that is used to run a command while the main bash shell waits for the result.</p> +<h2 id="parameters">Parameters</h2> +<p>There are three kind of parameters:</p> +<ol> +<li>Environment Parameter</li> +<li>Positional Parameter</li> +<li>Variables</li> +</ol> +<h3 id="environment-parameter">Environment Parameter</h3> +<p>environment variables exist at the process level. That means they are not a feature of the bash shell, but rather a feature of any program process on your system. They can inherit by children, but children’s EV can’t be given to parent.</p> +<h3 id="positional-parameter">Positional Parameter</h3> +<p>Just as name indicates, these kind of parameters indicate arguments’ position, and always starting from 0.</p> +<p>for example, imaging we have a script <code>rename</code>, arguments could be passed to it to extend its usage:</p> +<p><code>rename dir name</code> there, we passed <code>dir</code> and <code>name</code> as argument, so that positional parameters in script would be <code>$1</code> and <code>$2</code>, representing arguments respectively. after <code>$2</code>, such as <code>$3</code> is unset since there has no more argument.</p> +<blockquote> +<p>Positional Parameter is read-only</p> +</blockquote> +<p>a new usage: <code>bash -c 'ls "$1"' -- '/home'</code>. This will working like <code>ls /home</code>, dash is necessary since it is first variable in shell we ran commands and it makes positional value of arguments populated after it stand as we expect in shell single-quoted command gonna run in.</p> +<h3 id="special-parameter">Special Parameter</h3> +<p>Special parameters are parameters whose name is a single symbolic character, they are used to request certain state information from the bash shell. Like positional parameter, they are <em>read-only</em>.</p> +<p><img src="https://assets.garhve.com/pictures/screenshots/2022/10/1666054171.png" alt="different kinds of special parameters and the information they hold"></p> +<h3 id="variables">Variables</h3> +<p>definition: <code>name=value</code> <em>//no space around <code>=</code> like other programming language support</em></p> +<p>call: like <em>command expansion</em>, using variable is to expand it with prefix <code>$</code>, e.g. <code>$name</code></p> +<ul> +<li>Keep in mind, Expansion should always be double-quoted *</li> +</ul> +<h3 id="parameter-expansion">Parameter expansion</h3> +<blockquote> +<p><a href="https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html">GNU material</a></p> +</blockquote> +<p>we expand parameters by prefixing their name with a <code>$</code> symbol</p> +<blockquote> +<p>e.g. <code>name=me; echo hello "$name"</code>. <code>hello me</code>.</p> +</blockquote> +<p>In addition, we can put braces (<code>{</code> and <code>}</code>) around our parameter, which indicates where variable is about to begin and end.</p> +<blockquote> +<p>e.g. <code>name=orange; echo there are 4 "${name}s"</code> <code>there are 4 oranges</code>.</p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>name=orange +</span></span><span style="display:flex;"><span>echo <span style="font-style:italic">"there are 4 </span><span style="font-weight:bold;font-style:italic">${</span>name<span style="font-weight:bold;font-style:italic">}</span><span style="font-style:italic">s."</span> <span style="font-style:italic"># there are 4 oranges.</span> +</span></span><span style="display:flex;"><span>echo <span style="font-style:italic">"there are 4 </span>$names<span style="font-style:italic">."</span> <span style="font-style:italic"># there are 4 .</span> +</span></span></code></pre></div><p>here, we put <code>{}</code>around<code>name</code>so that bash can be told that suffix <code>s</code> is not a part of variable. otherwise, it will treat <code>names</code> as parameter and looking for its value, which is none in our example.</p> +</blockquote> +<p>parameter expansion brings up a powerful feature: <em>parameter expansion oerators</em></p> +<blockquote> +<p>While expanding a parameter, it is possible to apply an operator to the expanding value without alternate original value.</p> +<p>I use these mostly</p> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># remove string before pattern ${name#pattern} shortest ${name##pattern} longest</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># remove string after pattern ${name%pattern} longest ${name%%pattern} shortest</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># delete first matching pattern ${name/pattern}</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># delete all matching pattern ${name//pattern}</span> +</span></span><span style="display:flex;"><span><span style="font-style:italic"># substitute pattern with string ${name//pattern/string}</span> +</span></span><span style="display:flex;"><span> +</span></span><span style="display:flex;"><span>foo=<span style="font-style:italic">"foo-bar-foobar"</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo#*-<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'bar-foobar' (Removes 'foo-' because that matches '*-')</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo##*-<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'foobar' (Removes 'foo-bar-')</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo%-*<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'foo-bar'</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo%%-*<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'foo'</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo/-<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'foobar-foobar'</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo//-<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'foobarfoobar'</span> +</span></span><span style="display:flex;"><span>echo <span style="font-weight:bold;font-style:italic">${</span>foo//-/_<span style="font-weight:bold;font-style:italic">}</span> <span style="font-style:italic"># echoes 'foo_bar_foobar'</span> +</span></span></code></pre></div></blockquote> +<p><img src="https://assets.garhve.com/pictures/screenshots/2022/10/1665660923.png" alt="part of operators as shown picture"></p> + + </div> + + <div class="row"> + <div class="col-xs-12"> + + </div> + </div> + + + <div style="height: 50px;"></div> + + + <div class="site-footer"> + + + +</div> + + </div> + </div> + </article> + + + +<script> + + + + + +</script> + + + +</body> + +</html> |