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"description" : "Crontab crontab is a useful tool, I really regret that I don\u0026rsquo;t familar it earlier.\nIt\u0026rsquo;s usage really simple, and these two are my frequent using:\ncrontab -e #edit crontab file that reside in \/var\/spool\/cron crontab -l #list current crontab job It basic syntax as follow, also really simple example of usage:\ndelete file foo every minute * * * * * rm foo delete file foo every 15 minutes 15 * * * * rm foo delete file foo every beginning of hour 0 * * * * rm foo delete file foo every minute after 3 hours * 3 * * * rm foo delete file foo every day at 18:30 30 18 * * * rm foo delete file foo every beginning of month 0 0 0 * * rm foo delete file foo on beginning of 1st,10th of month 0 0 1,10 * * rm foo The usage really simple, I now use it to renew my SSL certification and daily update bt-tracker.",
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<title>Mess with bash(1)</title>
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<meta property="og:description" content="Crontab crontab is a useful tool, I really regret that I don&rsquo;t familar it earlier.
It&rsquo;s usage really simple, and these two are my frequent using:
crontab -e #edit crontab file that reside in /var/spool/cron crontab -l #list current crontab job It basic syntax as follow, also really simple example of usage:
delete file foo every minute * * * * * rm foo delete file foo every 15 minutes 15 * * * * rm foo delete file foo every beginning of hour 0 * * * * rm foo delete file foo every minute after 3 hours * 3 * * * rm foo delete file foo every day at 18:30 30 18 * * * rm foo delete file foo every beginning of month 0 0 0 * * rm foo delete file foo on beginning of 1st,10th of month 0 0 1,10 * * rm foo The usage really simple, I now use it to renew my SSL certification and daily update bt-tracker." />
<meta name="description" content="Crontab crontab is a useful tool, I really regret that I don&rsquo;t familar it earlier.
It&rsquo;s usage really simple, and these two are my frequent using:
crontab -e #edit crontab file that reside in /var/spool/cron crontab -l #list current crontab job It basic syntax as follow, also really simple example of usage:
delete file foo every minute * * * * * rm foo delete file foo every 15 minutes 15 * * * * rm foo delete file foo every beginning of hour 0 * * * * rm foo delete file foo every minute after 3 hours * 3 * * * rm foo delete file foo every day at 18:30 30 18 * * * rm foo delete file foo every beginning of month 0 0 0 * * rm foo delete file foo on beginning of 1st,10th of month 0 0 1,10 * * rm foo The usage really simple, I now use it to renew my SSL certification and daily update bt-tracker." />
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<h1 class="post-title">Mess with bash(1)</h1>
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<time class="post-date" datetime="2022-08-25 13:40:56 CST">
25 Aug 2022
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<a target="_blank" href="https://garhve.com">@garhve</a>
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<h3 id="crontab">Crontab</h3>
<p><code>crontab</code> is a useful tool, I really regret that I don’t familar it earlier.</p>
<p>It’s usage really simple, and these two are my frequent using:</p>
<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>crontab -e <span style="font-style:italic">#edit crontab file that reside in /var/spool/cron</span>
</span></span><span style="display:flex;"><span>crontab -l <span style="font-style:italic">#list current crontab job</span>
</span></span></code></pre></div><p>It basic syntax as follow, also really simple
<img src="https://assets.garhve.com/pictures/screenshots/2022/08/1857817000.jpg" alt="crontab-layout.jpg"></p>
<p>example of usage:</p>
<ol>
<li>delete file <em>foo</em> every minute
<code>* * * * * rm foo</code></li>
<li>delete file <em>foo</em> every 15 minutes
<code>15 * * * * rm foo</code></li>
<li>delete file <em>foo</em> every beginning of hour
<code>0 * * * * rm foo</code></li>
<li>delete file <em>foo</em> every minute after 3 hours
<code>* 3 * * * rm foo</code></li>
<li>delete file <em>foo</em> every day at 18:30
<code>30 18 * * * rm foo</code></li>
<li>delete file <em>foo</em> every beginning of month
<code>0 0 0 * * rm foo</code></li>
<li>delete file <em>foo</em> on beginning of 1st,10th of month
<code>0 0 1,10 * * rm foo</code></li>
</ol>
<p>The usage really simple, I now use it to renew my SSL certification and daily update bt-tracker.</p>
<hr>
<h3 id="tr">tr</h3>
<p><code>tr</code> is really useful when encountered situation that needs struggle with string.
Three frequency ways of using <code>tr</code></p>
<ol>
<li>
<p><strong>shrink</strong> multiple characters into single one</p>
<p><code>tr -s '[string]'</code>
e.g. <code>echo "ssssssspaaaaace" | tr -s 'sa'</code> would convert “ssssssspace” to “space”</p>
</li>
<li>
<p><strong>delete</strong> specific character. I usually use it to delete white space or delimiter</p>
<p><code>tr -d '[string]'</code>
e.g. <code>echo "blog.garhve.com" | tr -d '.o'</code> would convert url to “blggarhvecm”</p>
</li>
<li>
<p><strong>convert</strong> specific character to another one.</p>
<p><code>tr '[string1]' '[string2]'</code>
e.g. <code>echo "woopwon | tr "wo" "fe"</code> would result “feepfen”</p>
</li>
</ol>
<hr>
<h3 id="cut">cut</h3>
<p>I use <code>cut</code> mostly to get word from a string, especially get relative path from absolute path. Because I always want to loop to get same sub-directories file from different main directory, <code>cut</code> helps a lot.</p>
<p>for now, I only use it one way</p>
<p><code>echo string | cut -d '[character]' -f position</code>
e.g. <code>echo path/to/most/inner/file | cut -d '/' -f1</code> this will give me word before first ‘/’, which is ‘path’</p>
<p>Often, <code>rev</code> will co-work with <code>cut</code> to get last one word</p>
<p>e.g. <code>echo blog.garhve.com | rev | cut -d '.' -f 1 | rev</code> this will give word after last ‘/’, which is com.</p>
<blockquote>
<p><em>a worth noting here is that the <code>rev</code> command needs to appear twice because it usage is not so intuitive, it reverse whole string</em></p>
<p><code>echo "hello world" | rev</code> will get ‘dlrow olleh`</p>
<p><code>echo "hello world" | cut -d ' ' -f1 | rev</code> will give result of ‘dlrow’</p>
<p><code>echo "hello world" | rev | cut -d ' ' -f1</code> will give same result, as ‘dlrow’</p>
<p><code>echo "hello world" | rev | cut -d ' ' -f1 | rev</code> will give expected result, as ‘world’</p>
</blockquote>
<h3 id="daily-update-bt-tracker">Daily update bt tracker</h3>
<p>I already learn shell script for a while.. so I wrote a simple script to test whether I really got used to it, but result is obviously, I need more and more practice to memorize commands.</p>
<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="">#! /bin/sh
</span></span></span><span style="display:flex;"><span><span style=""></span><span style="font-style:italic">#bt-tracker.txt</span>
</span></span><span style="display:flex;"><span>site=https://raw.githubusercontent.com/ngosang/trackerslist/master/trackers_all.txt
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span>file=/path_to_aria_directory/aria2.conf
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span>Addr=user@addr
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="font-style:italic"># Get bt-tracker and format it to fulfill aria needs, then store in variable</span>
</span></span><span style="display:flex;"><span>bt=<span style="font-weight:bold">$(</span>curl $site | tr -s <span style="font-style:italic">'[:space:]'</span> | tr <span style="font-style:italic">'[:space:]'</span> <span style="font-style:italic">','</span><span style="font-weight:bold">)</span>
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span><span style="font-style:italic"># sshpass is a software, that can allow me pass ssh password as argument</span>
</span></span><span style="display:flex;"><span><span style="font-style:italic"># so that I don't need to wait prompt</span>
</span></span><span style="display:flex;"><span><span style="font-style:italic"># 410 is the line of bt tracker resides, I now no other way to replace it.</span>
</span></span><span style="display:flex;"><span><span style="font-weight:bold">$(</span>sshpass -p <span style="font-style:italic">'password'</span> ssh -T $Addr <span style="font-style:italic">"sed -i '410d' </span>$file<span style="font-style:italic"> | echo </span>$bt<span style="font-style:italic"> >> </span>$file<span style="font-style:italic">"</span><span style="font-weight:bold">)</span>
</span></span></code></pre></div><blockquote>
<p>Usage of <a href="https://blog.garhve.com/index.php/archives/23/#tr">tr</a> and <a href="https://blog.garhve.com/index.php/archives/23/#cut">cut</a>, expansion of ‘command tips’ is needed</p>
</blockquote>
<h3 id="ways-to-find-files-or-specific-string-in-files">Ways to find files or specific string in files</h3>
<p>In order to look up C definitions, I need to know where linux stores header files or which files store definitions I need. So that here comes up some methods to fulfill this need:</p>
<ol>
<li><code>find 'path' -name 'file_name'</code></li>
</ol>
<blockquote>
<p>e.g. <code>find / -name stdio.h</code> will return multiple location that stdio.h resides. this could expand to look for others</p>
<p><img src="https://assets.garhve.com/pictures/screenshots/2022/09/find_name.png" alt="image.png"></p>
<p>more info could see <code>man find</code></p>
</blockquote>
<hr>
<ol start="2">
<li><code>grep -rnw 'path' -e 'pattern'</code></li>
</ol>
<blockquote>
<p>e.g. `grep –include=*.{h,c} -rnw / -e “from_kuid” will return string and filename that contains string.</p>
<p><img src="https://assets.garhve.com/pictures/screenshots/2022/09/grep_string.png" alt="image.png"></p>
<ul>
<li><code>-r</code> or <code>-R</code> is recursive,</li>
<li><code>-n</code> is line number, and</li>
<li><code>-w</code> stands for match the whole word.</li>
<li><code>-l</code> (lower-case L) can be added to just give the file name of matching files.</li>
<li><code>-e</code> is the pattern used during the search</li>
</ul>
<p>Along with these, <code>--exclude</code>, <code>--include</code>, <code>--exclude-dir</code> flags could be used for efficient searching:</p>
<ul>
<li>This will only search through those files which have .c or .h extensions:</li>
</ul>
<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>grep --include=<span style="font-weight:bold;font-style:italic">\*</span>.{c,h} -rnw <span style="font-style:italic">'/path/to/somewhere/'</span> -e <span style="font-style:italic">"pattern"</span>
</span></span></code></pre></div><ul>
<li>This will exclude searching all the files ending with .o extension:</li>
</ul>
<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>grep --exclude=<span style="font-weight:bold;font-style:italic">\*</span>.o -rnw <span style="font-style:italic">'/path/to/somewhere/'</span> -e <span style="font-style:italic">"pattern"</span>
</span></span></code></pre></div><ul>
<li>For directories it’s possible to exclude one or more directories using the <code>--exclude-dir</code> parameter. For example, this will exclude the dirs dir1/, dir2/ and all of them matching *.dst/:</li>
</ul>
<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>grep --exclude-dir={dir1,dir2,*.dst} -rnw <span style="font-style:italic">'/path/to/somewhere/'</span> -e <span style="font-style:italic">"pattern"</span>
</span></span></code></pre></div><p>more info could see <a href="https://ss64.com/bash/grep.html"><code>man grep</code></a>.</p>
</blockquote>
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