Shell Scripting

This page has some notes about shell scripting.

If you need more info about shell scripting I would highly suggest O'Reilly Books .

I have found these O'Reilly Books useful

"Linux in a Nutshell" (http://www.oreilly.com/catalog/linuxnut5/)

"Unix in a Nutshell" (http://www.oreilly.com/catalog/unixnut4/)

"Bash Cookbook" (http://www.oreilly.com/catalog/9780596526788/)

White Space
When shell programming you often have commands that format output for the screen, often using spaces.  This can be problemic because it is not easy to remove the spaces from the values you want to use. For example look at the output from route -n

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.2.0.0        0.0.0.0         255.255.0.0     U     1      0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0
0.0.0.0         10.2.0.1        0.0.0.0         UG    0      0        0 eth0

you can see there are alot of spaces in that. So it can be difficult to

worse yet, it can be variable, ie the amount of space can change each time you run the commands; For example the

bdolango@bdolang-oldlaptop:~$ uptime
 12:50:58 up 1 day,  1:35,  4 users,  load average: 0.12, 0.16, 0.12

output from uptime will vary it's location based on how many users on the system. Not this isn't a impossible task, but it makes using the output a much more difficult, and often not worth progamming around.

Well I have a quick and easy fixx for this( I am certian I am not the first one to come up with this, but I found it SOOOO useful I thought I would write it down! [and I am certian I will forget it]). Throught the beatuy of shell programming you can just take your multi-spaced output and echo it, which will reduce your output to a single spaced output which is easily parsed with cut! For example if we take the output from uptime...

or the route example

pretty quick and efficient fixx for the problem.