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| author | garhve <git@garhve.com> | 2023-02-14 18:29:13 +0800 |
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| committer | garhve <git@garhve.com> | 2023-02-14 18:29:13 +0800 |
| commit | 734f042c9d99e0110d5e4cf8f2994a5ce27385d1 (patch) | |
| tree | 4b825dc642cb6eb9a060e54bf8d69288fbee4904 /public/post/mess-with-bash-2 | |
| parent | 92e08c404fa53f304dec7490c4acb4b45dd0d7df (diff) | |
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diff --git a/public/post/mess-with-bash-2/index.html b/public/post/mess-with-bash-2/index.html deleted file mode 100644 index 867eca3..0000000 --- a/public/post/mess-with-bash-2/index.html +++ /dev/null @@ -1,276 +0,0 @@ -<!DOCTYPE html> -<html lang="en"> - -<head> - <meta charset="utf-8"> - -<title>Mess with Bash(2) | garhve's gibberish</title> - - - <link rel="shortcut icon" type="image/png" href="/images/favicon.png"> - <meta name="viewport" content="width=device-width,initial-scale=1"> - - <link id="stylesheet" rel="stylesheet" type="text/css" href="/dark.css"> - - <script type="text/javascript" src="/js/theme.js"></script> - -</head> - -<div class="header"> - <div class="site_title"> - <p><a href="/"><img src="https://blog.garhve.com/images/logo.png" alt="garhve's gibberish" - width="70" height=auto></a></p> - <p><a href="/"> garhve's gibberish</a></p> - </div> - <div class="menu"> - <!-- <a href="/tags">tags</a> - --><a href="/categories">categories</a> - </div> -</div> - -<body onload="getTheme()"> - <section class="section"> - <div class="container"> - -<p> - <div class="title_postpage">Mess with Bash(2)</div> -</p> -<p> - <div class="date_postpage">2022-09-29</div> - <div class="taxonomies_postpage"> - - - <a href="https://blog.garhve.com/categories/code/">/code</a> - - - - -  <a href="https://blog.garhve.com/tags/bash/">#bash</a> - - - </div> -</p> - -<p> - <blockquote> -<p>More info is in this <a href="https://https://guide.bash.academy">tutorial</a> -Bash scripting <a href="https://devhints.io/bash">cheatsheet</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#616e88;"># exec can be used to change the file descriptors of bash itself, -</span><span style="color:#616e88;"># and if you use an x that doesn't yet exist, -</span><span style="color:#616e88;"># bash will create a new file descriptor ("plug") for you with that number. -</span><span style="color:#616e88;"># - in command is to close new FD 3 we'd created before. -</span><span style="color:#616e88;"># >&- is to close FD 1, <&- is to close FD0 -</span><span style="color:#88c0d0;">exec </span><span style="color:#b48ead;">3</span><span style="color:#81a1c1;">>&</span><span style="color:#b48ead;">1 </span><span style="color:#81a1c1;">></span><span>mylog</span><span style="color:#81a1c1;">; </span><span style="color:#88c0d0;">echo</span><span> moo</span><span style="color:#81a1c1;">; </span><span style="color:#88c0d0;">exec </span><span style="color:#b48ead;">1</span><span style="color:#81a1c1;">>&</span><span style="color:#b48ead;">3 3</span><span style="color:#81a1c1;">>&</span><span style="color:#eceff4;">- -</span></code></pre> -</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#81a1c1;"><<delimiter -</span><span style="color:#a3be8c;"> Here document -</span><span style="color:#81a1c1;">delimiter -</span></code></pre> -<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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#88c0d0;">cat </span><span style="color:#81a1c1;"><< EOF -</span><span style="color:#a3be8c;">this is within here document -</span><span style="color:#a3be8c;">I can write as many lines as I like -</span><span style="color:#a3be8c;">and terminate with line of demiliter only -</span><span style="color:#a3be8c;">EOF //end of heredoc -</span></code></pre> -</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#88c0d0;">cat </span><span style="color:#81a1c1;"><<< </span><span style="color:#a3be8c;">"This, -</span><span style="color:#a3be8c;">is the here strings. tab will also be read." -</span></code></pre> -</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#616e88;"># 3>&1-: copy FD 1 to FD 3 and close FD 1. -</span><span style="color:#616e88;"># >&3-: copy FD 3 to FD 1 and close FD 3. -</span><span style="color:#88c0d0;">exec </span><span style="color:#b48ead;">3</span><span style="color:#81a1c1;">>&</span><span style="color:#b48ead;">1</span><span>- </span><span style="color:#81a1c1;">></span><span>mylog</span><span style="color:#81a1c1;">; </span><span style="color:#88c0d0;">echo</span><span> moo</span><span style="color:#81a1c1;">; </span><span style="color:#88c0d0;">exec </span><span style="color:#81a1c1;">>&</span><span style="color:#b48ead;">3</span><span>- -</span></code></pre> -</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#88c0d0;">exec </span><span style="color:#b48ead;">5</span><span style="color:#81a1c1;"><></span><span>aFile -</span><span style="color:#88c0d0;">cat </span><span style="color:#81a1c1;">>&</span><span style="color:#b48ead;">5 </span><span style="color:#a3be8c;">"Hello world" </span><span style="color:#616e88;"># make FD 1 write to where FD 5 currently writing, copy file descriptor FD 5 to FD 1 -</span><span style="color:#88c0d0;">cat </span><span style="color:#81a1c1;"><&</span><span style="color:#b48ead;">5 </span><span style="color:#616e88;"># 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></code></pre> -</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#616e88;"># this will output contents in hello.h to screen -</span><span style="color:#88c0d0;">cat</span><span> hello.h -</span><span> -</span><span style="color:#616e88;"># this will expand `cat hello.h` to real contents in -</span><span style="color:#616e88;"># file hello.h and concatenate to previous sentence -</span><span style="color:#88c0d0;">echo </span><span style="color:#a3be8c;">"file hello.h contains contents of </span><span style="color:#81a1c1;">$</span><span style="color:#a3be8c;">(</span><span style="color:#88c0d0;">cat</span><span style="color:#a3be8c;"> hello.h)" -</span><span> -</span><span style="color:#616e88;"># this will output 'file hello.h contains contents of $(cat hello.h)' -</span><span style="color:#616e88;"># without expand command in $() -</span><span style="color:#88c0d0;">echo </span><span style="color:#a3be8c;">'file hello.h contains contents of $(cat hello.h)' -</span></code></pre> -<p>In command, <code>$()</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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span>name</span><span style="color:#81a1c1;">=</span><span style="color:#a3be8c;">orange -</span><span style="color:#88c0d0;">echo </span><span style="color:#a3be8c;">"there are 4 </span><span style="color:#81a1c1;">$</span><span style="color:#a3be8c;">{</span><span>name</span><span style="color:#a3be8c;">}s." </span><span style="color:#616e88;"># there are 4 oranges. -</span><span style="color:#88c0d0;">echo </span><span style="color:#a3be8c;">"there are 4 </span><span style="color:#81a1c1;">$</span><span>names</span><span style="color:#a3be8c;">." </span><span style="color:#616e88;"># there are 4 . -</span></code></pre> -<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> -<pre data-lang="bash" style="background-color:#2e3440;color:#d8dee9;" class="language-bash "><code class="language-bash" data-lang="bash"><span style="color:#616e88;"># remove string before pattern ${name#pattern} shortest ${name##pattern} longest -</span><span style="color:#616e88;"># remove string after pattern ${name%pattern} longest ${name%%pattern} shortest -</span><span style="color:#616e88;"># delete first matching pattern ${name/pattern} -</span><span style="color:#616e88;"># delete all matching pattern ${name//pattern} -</span><span style="color:#616e88;"># substitute pattern with string ${name//pattern/string} -</span><span> -</span><span>foo</span><span style="color:#81a1c1;">=</span><span style="color:#a3be8c;">"foo-bar-foobar" -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">#*</span><span>-} </span><span style="color:#616e88;"># echoes 'bar-foobar' (Removes 'foo-' because that matches '*-') -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">##*</span><span>-} </span><span style="color:#616e88;"># echoes 'foobar' (Removes 'foo-bar-') -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">%</span><span>-</span><span style="color:#81a1c1;">*</span><span>} </span><span style="color:#616e88;"># echoes 'foo-bar' -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">%%</span><span>-</span><span style="color:#81a1c1;">*</span><span>} </span><span style="color:#616e88;"># echoes 'foo' -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">/</span><span>-} </span><span style="color:#616e88;"># echoes 'foobar-foobar' -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">/</span><span>/-} </span><span style="color:#616e88;"># echoes 'foobarfoobar' -</span><span style="color:#88c0d0;">echo </span><span style="color:#81a1c1;">$</span><span>{foo</span><span style="color:#81a1c1;">/</span><span>/-</span><span style="color:#81a1c1;">/</span><span>_} </span><span style="color:#616e88;"># echoes 'foo_bar_foobar' -</span></code></pre> -</blockquote> -<p><img src="https://assets.garhve.com/pictures/screenshots/2022/10/1665660923.png" alt="part of operators as shown picture" /></p> - -</p> - - - - - </div> - </section> -</body> - -<div class="footer"> -  © garhve -</div> - -</html> |