Time Management for System Administrators

case '$i' in -h) usage shift ;; -a) AUTHOR='$2'; shift shift ;; -c) COPYRIGHT='$2'; shift shift ;; -d) DEBUG=true shift ;; --) shift; break;; esac done if $DEBUG ; then echo DEBUG MODE ENABLED. DEBUGCMD=echo fi # Make sure we have the minimum number of items on the command line. if $DEBUG ; then echo ITEM COUNT = $# ; fi if [ $# -lt '$MINITEMS' ]; then usage fi # If the first option is special, capture it: # THEITEM='$1' ; shift # Clone that line for each item you want to gather. # Make sure that you adjust the MINITEMS variable to suit your needs. # If you want to do something with each remaining item, do it here: #for i in $* ; do # echo Looky! Looky! I got $i #done if [ ! -z '$COPYRIGHT' ]; then if $DEBUG ; then echo Setting copyright to: $COPYRIGHT ; fi CRFLAG='-copyright $COPYRIGHT' fi LABEL='date -u +%Y%m%d' $DEBUGCMD mkisofs -D -l -J -r -L -f -P '$AUTHOR' -V $LABEL $CRFLAG $*

Building Up a Long Command Line

The best way to learn the Unix/Linux way of stringing commands together into one big pipe is to look over the shoulder of someone as she does it. I'll try to do that here by walking you through the steps I used to create a small utility.

Tip

Think Unix (Que) is an excellent book for learning how to link Unix/Linux tools to make bigger commands.

The single most powerful technology introduced by Unix/Linux is the ability to connect commands together like linking garden hoses. If you have one program that takes input and changes everything to uppercase, and another program that sorts the lines of a file, you can chain them together. The result is a command that converts the lines to uppercase and outputs the lines in sorted order. All you have to do is put a pipe symbol (|) between each command. The output of one command is fed into the next command: $ cat file | toupper | sort

For those of you unfamiliar with Unix/Linux, cat is the command that outputs a file. toupper is a program I wrote that changes text to uppercase. sort is the program that sorts lines of text. They all fit together quite nicely.

Let's use this to write a more complicated utility. How about a program that will determine which machine on your local network is most likely to be infected with a worm? We'll do it in one very long pipeline.

Sound amazing? Well, what this program will really do is find the hosts most likely to be infected—i.e., generate a list of which hosts require further investigation. However, I assure you that this technique will amaze your coworkers.