coproc help - a new feature in bash

In the <a class="zem_slink freebase/en/bash" title="Bash" rel="homepage" href="http://tiswww.case.edu/php/chet/bash/bashtop.html">bash version 4.0, there is a new concept called coproc. This is very useful for some of the daily tasks.

co-<a class="zem_slink freebase/guid/9202a8c04000641f800000000005a409" title="Process (computing)" rel="wikipedia" href="http://en.wikipedia.org/wiki/Process_%28computing%29">process starts a process in the background, optionally with a NAME, with which other processes can communicate. This can be a very <a class="zem_slink freebase/en/substitute_good" title="Substitute good" rel="wikipedia" href="http://en.wikipedia.org/wiki/Substitute_good">good substitution for <a class="zem_slink freebase/guid/9202a8c04000641f800000000048fac5" title="Pipeline (Unix)" rel="wikipedia" href="http://en.wikipedia.org/wiki/Pipeline_%28Unix%29">pipes in lots of cases. You can learn more about coproc in the link below:

Bash Sub Shells

Taken from <a href="http://www.linuxjournal.com/content/bash-sub-shells" target="_blank">here.

<span class=\"c\">#!/bin/bash</span>

<span class="nv">server_cmd</span><span class="o">=</span>server <span class="nv">pid_file</span><span class="o">=</span><span class="k">$(</span>basename <span class="nv">$server_cmd</span> .sh<span class="k">)</span>.pid <span class="nv">log_file</span><span class="o">=</span><span class="k">$(</span>basename <span class="nv">$server_cmd</span> .sh<span class="k">)</span>.log

<span class="o">(</span> <span class="nb">echo</span> <span class="s2">"Starting server"</span> <span class="nb">echo</span> <span class="s2">"Doing some init work"</span> <span class="nv">$server_cmd</span> <span class="c"># server becomes a daemon</span>

<span class=\"k\">while </span><span class=\"nb\">true</span>

<span class="nb"> </span><span class="k">do</span> <span class="k"> if</span> <span class="o">[[</span> -f <span class="nv">$pid_file</span> <span class="o">]]</span>; <span class="k">then</span> <span class="k"> </span>sleep 15 <span class="k">else</span> <span class="k"> </span><span class="nb">break</span> <span class="nb"> </span><span class="k">fi</span> <span class="k"> done</span> <span class="k"> </span>mail -s <span class="s2">"Server exitted"</span> joe@blow.com <<<CRAP

Splitting strings with IFS

Today I want to discuss splitting strings into tokens or “words”. I previously discussed how to do this with the <a href="http://bashcurescancer.com/reading-a-file-line-by-line.html">IFS variable and promised a more in depth discussion. Today, I will make the case on WHY to use IFS to split strings as opposed to using a subshell combined with <a class="zem_slink freebase/en/awk" title="AWK" rel="homepage" href="http://cm.bell-labs.com/cm/cs/awkbook/index.html">awk or cut.

I wrote this script which reads the /etc/password file line-by-line and prints the <a class="zem_slink freebase/en/user" title="User (computing)" rel="wikipedia" href="http://en.wikipedia.org/wiki/User_%28computing%29">username of any user which has a UID greater than 10 and has the shell of /sbin/nologin. Each test function performs this task 10 times to increase the length of the test: