Bash Scripts – Examples

I find it most useful when I approach any learning with a clear goal (or at least a specific enough task) to accomplish.

Here’s a list of simple Bash scripts that I think could be a useful learning exercise:

  • what’s your name? – asks for your name and then shows a greeting
  • hello, world! (that also shows hostname and list server IP addresses)
  • write a system info script – that shows you a hostname, disks usage, network interfaces and maybe system load
  • directory info – script that counts disks space taken up by a directory and shows number of files and number of directories in it
  • users info – show number of users on the system, their full names and home directories (all taken from /etc/passwd file)
  • list virtual hosts on your webserver – I actually have this as a login greeting on my webservers – small script that highlights which websites (domains) your server has in web server (Apache or Nginx) configuration.

Do you have any more examples of what you’d like to do in a Linux shell? If not, I’ll just start with the examples above. The plan is to replace each example name in the list above with a link to the Unix Tutorial post.



Unix scripts: how to sum numbers up

If you’re ever thought of summing up more than two numbers in shell script, perhaps this basic post will be a good start for your Unix scripting experiments.

Basic construction for summing up in shell scripts

In my Basic arithmetic operations in Unix shell post last year, I’ve shown you how to sum up two numbers:

SUM=$(($NUMBER1 + $NUMBER2)

using the same approach, it’s possible to calculate sums of as many numbers as you like, if you use one of the loops available in your shell.

Before we get started, let’s create a simple file with numbers we’ll work with:

ubuntu$ for i in 1 2 3 4 5 6 7 8 9; do echo $i >> /tmp/nums; done;
ubuntu$ cat /tmp/nums
1
2
3
4
5
6
7
8
9

Using a while loop to sum numbers up in Unix

Here’s an example of how you can use a while loop in Unix shell for summing numbers up. Save it as a /tmp/sum.sh script, and don’t forget to do chmod a+x /tmp/sum.sh so that you can run it!

#!/bin/sh
#
SUM=0
#
while read NUM
do
        echo "SUM: $SUM";
        SUM=$(($SUM + $NUM));
        echo "+ $NUM: $SUM";
done < /tmp/nums

Here’s how the output will look when you run it:

ubuntu$ /tmp/sum.sh
SUM: 0
+ 1: 1
SUM: 1
+ 2: 3
SUM: 3
+ 3: 6
SUM: 6
+ 4: 10
SUM: 10
+ 5: 15
SUM: 15
+ 6: 21
SUM: 21
+ 7: 28
SUM: 28
+ 8: 36
SUM: 36
+ 9: 45

Of course, your data will most probably will be in a less readable form, so you’ll have to do a bit of parsing before you get to sum the numbers up, but the loop will be organized in the same way.

That’s it for today, enjoy and feel free to ask questions!

See also: