Yesterday a 20 line shell script caught a race condition in one of software I work on. Our best engineers looked at the problem, a vendor case was filed, and there was thoughts of automatically restarted the application to fix the issue at hand.

In the end, a 20 line shell script to strace for file operations continuously provided the needed visibility into the issue at hand.

Update: The shell script.

The shell script itself, though trivial, is owned by the company I work for, but the basic concept was as follows:

#!/bin/bash

nixcraft has a link on how to read a file line by line. The method is a great way to read a file, but there some trouble spots I thought I would point out.

In the script, the special variable IFS is set:

# set the Internal Field Separator to a pipe symbol
IFS='|'

The tells the read command to split “cyberciti.biz|74.86.48.99″ into “cyberciti.biz” and “74.86.48.99″ and thus fill both the domain and ip variables here:

Today I want to discuss splitting strings into tokens or “words”. I previously discussed how to do this with the 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 awk or cut.