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+ <div class="sidebar-scrollbox">
+ <ol class="chapter"><li class="chapter-item expanded affix "><a href="../intro.html">Introduction</a></li><li class="chapter-item expanded "><a href="../shells/index.html"><strong aria-hidden="true">1.</strong> Shells</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../shells/zsh.html"><strong aria-hidden="true">1.1.</strong> zsh</a></li><li class="chapter-item expanded "><a href="../shells/bash.html" class="active"><strong aria-hidden="true">1.2.</strong> bash</a></li><li class="chapter-item expanded "><a href="../shells/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li></ol></li><li class="chapter-item expanded "><a href="../cli/index.html"><strong aria-hidden="true">2.</strong> CLI foo</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../cli/awk.html"><strong aria-hidden="true">2.1.</strong> awk</a></li><li class="chapter-item expanded "><a href="../cli/sed.html"><strong aria-hidden="true">2.2.</strong> sed</a></li><li class="chapter-item expanded "><a href="../cli/column.html"><strong aria-hidden="true">2.3.</strong> column</a></li><li class="chapter-item expanded "><a href="../cli/sort.html"><strong aria-hidden="true">2.4.</strong> sort</a></li><li class="chapter-item expanded "><a href="../cli/tr.html"><strong aria-hidden="true">2.5.</strong> tr</a></li></ol></li><li class="chapter-item expanded "><a href="../tools/index.html"><strong aria-hidden="true">3.</strong> Tools</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">3.1.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/emacs.html"><strong aria-hidden="true">3.2.</strong> emacs</a></li><li class="chapter-item expanded "><a href="../tools/gpg.html"><strong aria-hidden="true">3.3.</strong> gpg</a></li><li class="chapter-item expanded "><a href="../tools/radare2.html"><strong aria-hidden="true">3.4.</strong> radare2</a></li><li class="chapter-item expanded "><a href="../tools/qemu.html"><strong aria-hidden="true">3.5.</strong> qemu</a></li><li class="chapter-item expanded "><a href="../tools/pacman.html"><strong aria-hidden="true">3.6.</strong> pacman</a></li><li class="chapter-item expanded "><a href="../tools/dot.html"><strong aria-hidden="true">3.7.</strong> dot</a></li><li class="chapter-item expanded "><a href="../tools/ffmpeg.html"><strong aria-hidden="true">3.8.</strong> ffmpeg</a></li><li class="chapter-item expanded "><a href="../tools/gnuplot.html"><strong aria-hidden="true">3.9.</strong> gnuplot</a></li><li class="chapter-item expanded "><a href="../tools/restic.html"><strong aria-hidden="true">3.10.</strong> restic</a></li></ol></li><li class="chapter-item expanded "><a href="../monitor/index.html"><strong aria-hidden="true">4.</strong> Resource analysis & monitor</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../monitor/lsof.html"><strong aria-hidden="true">4.1.</strong> lsof</a></li><li class="chapter-item expanded "><a href="../monitor/pidstat.html"><strong aria-hidden="true">4.2.</strong> pidstat</a></li><li class="chapter-item expanded "><a href="../monitor/pgrep.html"><strong aria-hidden="true">4.3.</strong> pgrep</a></li><li class="chapter-item expanded "><a href="../monitor/ps.html"><strong aria-hidden="true">4.4.</strong> ps</a></li><li class="chapter-item expanded "><a href="../monitor/pmap.html"><strong aria-hidden="true">4.5.</strong> pmap</a></li><li class="chapter-item expanded "><a href="../monitor/pstack.html"><strong aria-hidden="true">4.6.</strong> pstack</a></li></ol></li><li class="chapter-item expanded "><a href="../trace_profile/index.html"><strong aria-hidden="true">5.</strong> Trace and Profile</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trace_profile/time.html"><strong aria-hidden="true">5.1.</strong> time</a></li><li class="chapter-item expanded "><a href="../trace_profile/strace.html"><strong aria-hidden="true">5.2.</strong> strace</a></li><li class="chapter-item expanded "><a href="../trace_profile/ltrace.html"><strong aria-hidden="true">5.3.</strong> ltrace</a></li><li class="chapter-item expanded "><a href="../trace_profile/perf.html"><strong aria-hidden="true">5.4.</strong> perf</a></li><li class="chapter-item expanded "><a href="../trace_profile/oprofile.html"><strong aria-hidden="true">5.5.</strong> OProfile</a></li><li class="chapter-item expanded "><a href="../trace_profile/callgrind.html"><strong aria-hidden="true">5.6.</strong> callgrind</a></li></ol></li><li class="chapter-item expanded "><a href="../debug/index.html"><strong aria-hidden="true">6.</strong> Debug</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../debug/gdb.html"><strong aria-hidden="true">6.1.</strong> gdb</a></li><li class="chapter-item expanded "><a href="../debug/gdbserver.html"><strong aria-hidden="true">6.2.</strong> gdbserver</a></li></ol></li><li class="chapter-item expanded "><a href="../binary/index.html"><strong aria-hidden="true">7.</strong> Binary</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binary/od.html"><strong aria-hidden="true">7.1.</strong> od</a></li><li class="chapter-item expanded "><a href="../binary/xxd.html"><strong aria-hidden="true">7.2.</strong> xxd</a></li><li class="chapter-item expanded "><a href="../binary/readelf.html"><strong aria-hidden="true">7.3.</strong> readelf</a></li><li class="chapter-item expanded "><a href="../binary/objdump.html"><strong aria-hidden="true">7.4.</strong> objdump</a></li><li class="chapter-item expanded "><a href="../binary/nm.html"><strong aria-hidden="true">7.5.</strong> nm</a></li></ol></li><li class="chapter-item expanded "><a href="../development/index.html"><strong aria-hidden="true">8.</strong> Development</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/c++filt.html"><strong aria-hidden="true">8.1.</strong> c++filt</a></li><li class="chapter-item expanded "><a href="../development/c++.html"><strong aria-hidden="true">8.2.</strong> c++</a></li><li class="chapter-item expanded "><a href="../development/glibc.html"><strong aria-hidden="true">8.3.</strong> glibc</a></li><li class="chapter-item expanded "><a href="../development/gcc.html"><strong aria-hidden="true">8.4.</strong> gcc</a></li><li class="chapter-item expanded "><a href="../development/git.html"><strong aria-hidden="true">8.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../development/cmake.html"><strong aria-hidden="true">8.6.</strong> cmake</a></li><li class="chapter-item expanded "><a href="../development/make.html"><strong aria-hidden="true">8.7.</strong> make</a></li><li class="chapter-item expanded "><a href="../development/ld.so.html"><strong aria-hidden="true">8.8.</strong> ld.so</a></li><li class="chapter-item expanded "><a href="../development/symbolver.html"><strong aria-hidden="true">8.9.</strong> symbol versioning</a></li><li class="chapter-item expanded "><a href="../development/python.html"><strong aria-hidden="true">8.10.</strong> python</a></li><li class="chapter-item expanded "><a href="../development/gcov.html"><strong aria-hidden="true">8.11.</strong> gcov</a></li><li class="chapter-item expanded "><a href="../development/pgo.html"><strong aria-hidden="true">8.12.</strong> pgo</a></li></ol></li><li class="chapter-item expanded "><a href="../linux/index.html"><strong aria-hidden="true">9.</strong> Linux</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../linux/systemd.html"><strong aria-hidden="true">9.1.</strong> systemd</a></li><li class="chapter-item expanded "><a href="../linux/coredump.html"><strong aria-hidden="true">9.2.</strong> coredump</a></li><li class="chapter-item expanded "><a href="../linux/ptrace_scope.html"><strong aria-hidden="true">9.3.</strong> ptrace_scope</a></li><li class="chapter-item expanded "><a href="../linux/cryptsetup.html"><strong aria-hidden="true">9.4.</strong> cryptsetup</a></li><li class="chapter-item expanded "><a href="../linux/swap.html"><strong aria-hidden="true">9.5.</strong> swap</a></li><li class="chapter-item expanded "><a href="../linux/input.html"><strong aria-hidden="true">9.6.</strong> input</a></li><li class="chapter-item expanded "><a href="../linux/acl.html"><strong aria-hidden="true">9.7.</strong> acl</a></li><li class="chapter-item expanded "><a href="../linux/zfs.html"><strong aria-hidden="true">9.8.</strong> zfs</a></li></ol></li><li class="chapter-item expanded "><a href="../network/index.html"><strong aria-hidden="true">10.</strong> Network</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../network/ss.html"><strong aria-hidden="true">10.1.</strong> ss</a></li><li class="chapter-item expanded "><a href="../network/tcpdump.html"><strong aria-hidden="true">10.2.</strong> tcpdump</a></li><li class="chapter-item expanded "><a href="../network/tshark.html"><strong aria-hidden="true">10.3.</strong> tshark</a></li><li class="chapter-item expanded "><a href="../network/firewall-cmd.html"><strong aria-hidden="true">10.4.</strong> firewall-cmd</a></li><li class="chapter-item expanded "><a href="../network/nftables.html"><strong aria-hidden="true">10.5.</strong> nftables</a></li></ol></li><li class="chapter-item expanded "><a href="../web/index.html"><strong aria-hidden="true">11.</strong> Web</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../web/html.html"><strong aria-hidden="true">11.1.</strong> html</a></li><li class="chapter-item expanded "><a href="../web/css.html"><strong aria-hidden="true">11.2.</strong> css</a></li><li class="chapter-item expanded "><a href="../web/chartjs.html"><strong aria-hidden="true">11.3.</strong> chartjs</a></li></ol></li><li class="chapter-item expanded "><a href="../arch/index.html"><strong aria-hidden="true">12.</strong> Arch</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../arch/x86_64.html"><strong aria-hidden="true">12.1.</strong> x86_64</a></li><li class="chapter-item expanded "><a href="../arch/armv8.html"><strong aria-hidden="true">12.2.</strong> armv8</a></li><li class="chapter-item expanded "><a href="../arch/arm64.html"><strong aria-hidden="true">12.3.</strong> arm64</a></li><li class="chapter-item expanded "><a href="../arch/armv7.html"><strong aria-hidden="true">12.4.</strong> armv7</a></li><li class="chapter-item expanded "><a href="../arch/riscv.html"><strong aria-hidden="true">12.5.</strong> riscv</a></li></ol></li></ol>
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+ <div id="content" class="content">
+ <main>
+ <h1 id="bash1"><a class="header" href="#bash1">bash(1)</a></h1>
+<h2 id="expansion"><a class="header" href="#expansion">Expansion</a></h2>
+<h3 id="generator"><a class="header" href="#generator">Generator</a></h3>
+<pre><code class="language-bash"># generate sequence from n to m
+{n..m}
+# generate sequence from n to m step by s
+{n..m..s}
+
+# expand cartesian product
+{a,b}{c,d}
+</code></pre>
+<h3 id="parameter"><a class="header" href="#parameter">Parameter</a></h3>
+<pre><code class="language-bash"># default value
+bar=${foo:-some_val} # if $foo set, then bar=$foo else bar=some_val
+
+# alternate value
+bar=${foo:+bla $foo} # if $foo set, then bar="bla $foo" else bar=""
+
+# check param set
+bar=${foo:?msg} # if $foo set, then bar=$foo else exit and print msg
+
+# indirect
+FOO=foo
+BAR=FOO
+bar=${!BAR} # deref value of BAR -&gt; bar=$FOO
+
+# prefix
+${foo#prefix} # remove prefix when expanding $foo
+# suffix
+${foo%suffix} # remove suffix when expanding $foo
+
+# substitute
+${foo/pattern/string} # replace pattern with string when expanding foo
+# pattern starts with
+# '/' replace all occurences of pattern
+# '#' pattern match at beginning
+# '%' pattern match at end
+
+# set programmatically with priintf builtin
+printf -v "VAR1" "abc"
+NAME=VAR2
+printf -v "$NAME" "%s" "def"
+</code></pre>
+<blockquote>
+<p>Note: <code>prefix</code>/<code>suffix</code>/<code>pattern</code> are expanded as <a href="#pathname">pathnames</a>.</p>
+</blockquote>
+<h3 id="pathname"><a class="header" href="#pathname">Pathname</a></h3>
+<pre><code class="language-bash">* match any string
+? match any single char
+\\ match backslash
+[abc] match any char of 'a' 'b' 'c'
+[a-z] match any char between 'a' - 'z'
+[^ab] negate, match all not 'a' 'b'
+[:class:] match any char in class, available:
+ alnum,alpha,ascii,blank,cntrl,digit,graph,lower,
+ print,punct,space,upper,word,xdigit
+</code></pre>
+<p>With <code>extglob</code> shell option enabled it is possible to have more powerful
+patterns. In the following <code>pattern-list</code> is one ore more patterns separated
+by <code>|</code> char.</p>
+<pre><code class="language-bash">?(pattern-list) matches zero or one occurrence of the given patterns
+*(pattern-list) matches zero or more occurrences of the given patterns
++(pattern-list) matches one or more occurrences of the given patterns
+@(pattern-list) matches one of the given patterns
+!(pattern-list) matches anything except one of the given patterns
+</code></pre>
+<blockquote>
+<p>Note: <code>shopt -s extglob</code>/<code>shopt -u extglob</code> to enable/disable <code>extglob</code>
+option.</p>
+</blockquote>
+<h2 id="io-redirection"><a class="header" href="#io-redirection">I/O redirection</a></h2>
+<blockquote>
+<p>Note: The trick with bash I/O redirection is to interpret from left-to-right.</p>
+</blockquote>
+<pre><code class="language-bash"># stdout &amp; stderr to file
+command &gt;file 2&gt;&amp;1
+# equivalent
+command &amp;&gt;file
+
+# stderr to stdout &amp; stdout to file
+command 2&gt;&amp;1 &gt;file
+</code></pre>
+<blockquote>
+<p>The article <a href="https://catonmat.net/bash-one-liners-explained-part-three">Bash One-Liners Explained, Part III: All about
+redirections</a>
+contains some nice visualization to explain bash redirections.</p>
+</blockquote>
+<h3 id="explanation"><a class="header" href="#explanation">Explanation</a></h3>
+<pre><code class="language-bash">j&gt;&amp;i
+</code></pre>
+<p>Duplicate <code>fd i</code> to <code>fd j</code>, making <code>j</code> a copy of <code>i</code>. See <a href="http://man7.org/linux/man-pages/man2/dup.2.html">dup2(2)</a>.</p>
+<p>Example:</p>
+<pre><code class="language-bash">command 2&gt;&amp;1 &gt;file
+</code></pre>
+<ol>
+<li>duplicate <code>fd 1</code> to <code>fd 2</code>, effectively redirecting <code>stderr</code> to <code>stdout</code></li>
+<li>redirect <code>stdout</code> to <code>file</code></li>
+</ol>
+<h2 id="process-substitution-ref"><a class="header" href="#process-substitution-ref">Process substitution (<a href="https://tldp.org/LDP/abs/html/process-sub.html">ref</a>)</a></h2>
+<p>Process substitution allows to redirect the stdout of multiple processes at
+once.</p>
+<pre><code class="language-bash">vim -d &lt;(grep foo bar) &lt;(grep foo moose)
+</code></pre>
+<h2 id="command-grouping"><a class="header" href="#command-grouping">Command grouping</a></h2>
+<p>Execute commands in a group with or without subshell. Can be used to easily
+redirect stdout/stderr of all commands in the group into one file.</p>
+<pre><code class="language-bash"># Group commands without subshell.
+v=abc ; { v=foo; echo $v; } ; echo $v
+# foo
+# foo
+
+# Group commands with subshell.
+v=abc ; ( v=foo; echo $v; ) ; echo $v
+# foo
+# abc
+</code></pre>
+<h2 id="argument-parsing-with-getopts"><a class="header" href="#argument-parsing-with-getopts">Argument parsing with <code>getopts</code></a></h2>
+<p>The <code>getopts</code> builtin uses following global variables:</p>
+<ul>
+<li><code>OPTARG</code>, value of last option argument</li>
+<li><code>OPTIND</code>, index of the next argument to process (user must reset)</li>
+<li><code>OPTERR</code>, display errors if set to <code>1</code></li>
+</ul>
+<pre><code class="language-bash">getopts &lt;optstring&gt; &lt;param&gt; [&lt;args&gt;]
+</code></pre>
+<ul>
+<li><code>&lt;optstring&gt;</code> specifies the names of supported options, eg <code>f:c</code>
+<ul>
+<li><code>f:</code> means <code>-f</code> option with an argument</li>
+<li><code>c</code> means <code>-c</code> option without an argument</li>
+</ul>
+</li>
+<li><code>&lt;param&gt;</code> specifies a variable name which <code>getopts</code> fills with the last parsed option argument</li>
+<li><code>&lt;args&gt;</code> optionally specify argument string to parse, by default <code>getopts</code> parses <code>$@</code></li>
+</ul>
+<h3 id="example"><a class="header" href="#example">Example</a></h3>
+<pre><code class="language-bash">#!/bin/bash
+function parse_args() {
+ while getopts "f:c" PARAM; do
+ case $PARAM in
+ f) echo "GOT -f $OPTARG";;
+ c) echo "GOT -c";;
+ *) echo "ERR: print usage"; exit 1;;
+ esac
+ done
+ # users responsibility to reset OPTIND
+ OPTIND=1
+}
+
+parse_args -f xxx -c
+parse_args -f yyy
+</code></pre>
+<h2 id="regular-expressions"><a class="header" href="#regular-expressions">Regular Expressions</a></h2>
+<p>Bash supports regular expression matching with the binary operator <code>=~</code>.
+The match results can be accessed via the <code>$BASH_REMATCH</code> variable:</p>
+<ul>
+<li><code>${BASH_REMATCH[0]}</code> contains the full match</li>
+<li><code>${BASH_REMATCH[1]}</code> contains match of the first capture group</li>
+</ul>
+<pre><code class="language-bash">INPUT='title foo : 1234'
+REGEX='^title (.+) : ([0-9]+)$'
+if [[ $INPUT =~ $REGEX ]]; then
+ echo "${BASH_REMATCH[0]}" # title foo : 1234
+ echo "${BASH_REMATCH[1]}" # foo
+ echo "${BASH_REMATCH[2]}" # 1234
+fi
+</code></pre>
+<blockquote>
+<p><strong>Caution</strong>: When specifying a <code>regex</code> in the <code>[[ ]]</code> block directly, quotes will be treated as part of the pattern.
+<code>[[ $INPUT =~ "foo" ]]</code> will match against <code>"foo"</code> not <code>foo</code>!</p>
+</blockquote>
+<h2 id="completion"><a class="header" href="#completion">Completion</a></h2>
+<p>The <code>complete</code> builtin is used to interact with the completion system.</p>
+<pre><code class="language-bash">complete # print currently installed completion handler
+complete -F &lt;func&gt; &lt;cmd&gt; # install &lt;func&gt; as completion handler for &lt;cmd&gt;
+complete -r &lt;cmd&gt; # uninstall completion handler for &lt;cmd&gt;
+</code></pre>
+<p>Variables available in completion functions:</p>
+<pre><code class="language-bash"># in
+$1 # &lt;cmd&gt;
+$2 # current word
+$3 # privous word
+
+COMP_WORDS # array with current command line words
+COMP_CWORD # index into COMP_WORDS with current cursor position
+
+# out
+COMPREPLY # array with possible completions
+</code></pre>
+<p>The <code>compgen</code> builtin is used to generate possible matches by comparing <code>word</code>
+against words generated by <code>option</code>.</p>
+<pre><code class="language-bash">compgen &lt;option&gt; &lt;word&gt;
+
+# usefule options:
+# -W &lt;list&gt; specify list of possible completions
+# -d generate list with dirs
+# -f generate list with files
+# -u generate list with users
+# -e generate list with exported variables
+
+# compare "f" against words "foo" "foobar" "bar" and generate matches
+compgen -W "foo foobar bar" "f"
+
+# compare "hom" against file/dir names and generate matches
+compgen -d -f "hom"
+</code></pre>
+<h3 id="example-1"><a class="header" href="#example-1">Example</a></h3>
+<p>Skeleton to copy/paste for writing simple completions.</p>
+<p>Assume a program <code>foo</code> with the following interface:</p>
+<pre><code class="language-bash">foo -c green|red|blue -s low|high -f &lt;file&gt; -h
+</code></pre>
+<p>The completion handler could be implemented as follows:</p>
+<pre><code class="language-bash">function _foo() {
+ local curr=$2
+ local prev=$3
+
+ local opts="-c -s -f -h"
+ case $prev in
+ -c) COMPREPLY=( $(compgen -W "green red blue" -- $curr) );;
+ -s) COMPREPLY=( $(compgen -W "low high" -- $curr) );;
+ -f) COMPREPLY=( $(compgen -f -- $curr) );;
+ *) COMPREPLY=( $(compgen -W "$opts" -- $curr) );;
+ esac
+}
+
+complete -F _foo foo
+</code></pre>
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