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<h1><a class="header" href="#bash1" id="bash1">bash(1)</a></h1>
<h2><a class="header" href="#expansion" id="expansion">Expansion</a></h2>
<h3><a class="header" href="#generator" id="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><a class="header" href="#parameter" id="parameter">Parameter</a></h3>
<pre><code class="language-bash"># default param
bar=${foo:-some_val} # if $foo set, then bar=$foo else bar=some_val
# check param set
bar=${foo:?msg} # if $foo set, then bar=$foo else exit and print msg
# indirect
FOO=foo
BAR=FOO
bar=${!BAR} # deref value of BAR -> bar=$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
</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><a class="header" href="#pathname" id="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>Wit <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><a class="header" href="#io-redirection" id="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 & stderr to file
command >file 2>&1
# equivalent
command &>file
# stderr to stdout & stdout to file
command 2>&1 >file
</code></pre>
<h3><a class="header" href="#explanation" id="explanation">Explanation</a></h3>
<pre><code class="language-bash">j>&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>&1 >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><a class="header" href="#completion" id="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 <func> <cmd> # install <func> as completion handler for <cmd>
complete -r <cmd> # uninstall completion handler for <cmd>
</code></pre>
<p>Variables available in completion functions:</p>
<pre><code class="language-bash"># in
$1 # <cmd>
$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 [option] [word]
# usefule options:
# -W <list> 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><a class="header" href="#example" id="example">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 <file> -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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