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<div class="section" id="bash-tricks-with-find-and-sed">
<h1>Bash tricks with <em>find</em> and <em>sed</em><a class="headerlink" href="#bash-tricks-with-find-and-sed" title="Permalink to this headline">¶</a></h1>
<p>This article shows two <em>bash</em> tricks with <em>find</em> and <em>sed</em>. The
problem at hand is computing the number of lines in multiple files
in a directory. There is no subdirectory but the files have a one line
header that should not be part of the count.</p>
<ul class="simple">
<li><strong>sed</strong> will help operating on each file to omit the first line,</li>
<li><strong>find</strong> will help executing the sed command on every files of a
directory</li>
</ul>
<p>Let’s create a directory examples with two files:</p>
<div class="highlight-bash"><pre>~$ mkdir papa && cd papa
~$
~$ cat > tata # Type Ctrl-D to stop editing
# header
1
2
3
4
~$ cat > titi
# HEAD
1
2
~$ cat titi
# HEAD
1
2</pre>
</div>
<p><em>sed</em> operates on lines which are specified with an address range:
<em>first,last</em>. <em>sed</em> counts from one, not zero. The special
character <tt class="docutils literal"><span class="pre">$</span></tt> means the number of the <em>last line</em>. So to operate on
every line except the first one, the address range is <tt class="docutils literal"><span class="pre">'2,$'</span></tt>. Do
not forget the single quotes to prevent bash from messing with the
<tt class="docutils literal"><span class="pre">$</span></tt>.</p>
<p>Now that a range is specified, a command must be given: in our case,
it is the command <tt class="docutils literal"><span class="pre">p</span></tt> (for print).</p>
<div class="highlight-sh"><div class="highlight"><pre>~<span class="nv">$ </span>sed <span class="s1">'2,$p'</span> tata
<span class="c"># header</span>
1
1
2
2
3
3
4
4
</pre></div>
</div>
<p>One more thing, <em>sed</em>‘s default behavior is to print every line it
meets, regardless of what else it may do with it. The <tt class="docutils literal"><span class="pre">-n</span></tt> option
deactivates this (a.k.a. <tt class="docutils literal"><span class="pre">--silent</span></tt>):</p>
<div class="highlight-sh"><div class="highlight"><pre>~<span class="nv">$ </span>sed -n <span class="s1">'2,$p'</span> tata
1
2
3
4
~<span class="nv">$ </span>sed --silent <span class="s1">'2,$p'</span> tata
1
2
3
4
</pre></div>
</div>
<p>Fine for <em>sed</em>, now on to <em>find</em>. <em>find</em> can be restricted to <em>find</em>
only normal files with the option <tt class="docutils literal"><span class="pre">-type</span> <span class="pre">f</span></tt>, so that no directory
gets shown.</p>
<div class="highlight-sh"><div class="highlight"><pre>~<span class="nv">$ </span>find
.
./tata
./titi
~<span class="nv">$ </span>find -type f
./tata
./titi
</pre></div>
</div>
<p>Now, for each of these files, the previous <em>sed</em> command must be
EXECuted. <em>find</em> has the <tt class="docutils literal"><span class="pre">-exec</span></tt> option whose value is a command to
be executed for each file found. The name of the file found is
inserted here in the command with the <tt class="docutils literal"><span class="pre">'{}'</span></tt> pattern. A <tt class="docutils literal"><span class="pre">;</span></tt>
<em>terminator</em> character must be written at the end of the command so
that <em>find</em> knows when the command ends. The semi-colon must be
protected from mangling from bash with either <tt class="docutils literal"><span class="pre">\;</span></tt> or <tt class="docutils literal"><span class="pre">';'</span></tt>.</p>
<div class="highlight-sh"><div class="highlight"><pre>~<span class="nv">$ </span>find -type f -exec <span class="nb">echo</span> <span class="s2">"I found {}"</span> <span class="se">\;</span>
I found ./tata
I found ./titi
</pre></div>
</div>
<p>Now here is the command to count the lines of every file in the directory,
while omitting the header:</p>
<div class="highlight-sh"><div class="highlight"><pre>~<span class="nv">$ </span>find -type f -exec sed -n <span class="s1">'2,$p'</span> <span class="s1">'{}'</span> <span class="se">\;</span> | wc -l
6
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