Emergency UNIX and Linux Support

Shell scripting bridges and enhances the space between application programming and the UNIX OS. Many trivial one- or few-time tasks are better done in a wrapper script than in code, making the testing of the code bits much simpler and the code more robust. Also, unplanned activities are easily, predictable and safely accommodated by modified scripts and unmodified code, like catch up after an outage and similar production support tasks. Shell scripting is really the way to go for all sorts of ad-hoc reports, including data analysis to support design decisions by business case.

I write a lot of simple C to support shell with high performance features that are otherwise lacking, so the shell script can do high volumes of data by having C bits do the heavy lifting. Error handling: detecting, alerting and reporting is better done in a shell script, so:
Many housekeeping tasks for the system or the application space are better done in scripting, like compressing, backing up and purging old files. Scripting skills are mostly common with keyboard shell skills, so there is synergy in them: most tricks yo learn interactively can support a script that runs unattended or automates that interactive task.

It is not necessary to master every fine detail of any shell (which you will forget if you do not use), but pick a good one like ksh or bash, and look for the sweet spots you can imagine using. Some are very powerful and subtle, like the ability of (..) sub-shells to either concatenate output or divide input or both without handling a single byte, by the inheritance of FDs. For instance, these two scripts to pass a header line and sort the remaining lines are equivalent, but the second is:

Code:

some_code >/tmp/xxx.tmp
head -1 /tmp/xxx.tmp
tail +2 /tmp/xxx.tmp | sort
rm -f /tmp/xxx.tmp

some_code |(
line
exec sort
)

On a UNIX system? Pretty important. That terminal you're typing commands into all the time is a shell, and it's capable of much more useful and complicated work than just running something when you hit enter. You can use real constructs, even when just typing into the console directly.

It can do a lot of work for you. Some simple shell constructs are exceedingly useful:

Code:

# do something, then only if it succeeds, do something else
install-update && /sbin/reboot
# do something, and if it fails, do something else
mangle-the-world || putback-the-world
# do a repetitive task without typing it 9 times
for N in 1 2 3 4 5 6 7 8 9
do
        something-repetitive $N
done