The Previous following
articles of ‘Shell Scripting‘ series were highly appreciated and hence I am writing this
article to extend the never ending process of learning.
Bash Keywords
A keyword is a word or symbol that
has a special meaning to a computer language. The following symbols and words
have special meanings to Bash when they are
unquoted and the first word of a command.
case fi then [[
do for until ]]
done function while elif
if time else in {
Unlike
most computer languages, Bash allows keywords to
be used as variable names even
though this can make scripts difficult to read. To keep scripts understandable,
key-words should not be used for variable names.
A
command is implemented in shell as $(command). You might have to
include the full path of command. e.g., $(/bin/date), for
correct execution.
You may know the path of specific program using ‘whereis‘ command. e.g., whereis date
date: /bin/date /usr/share/man/man1/date.1.gz
That’s enough for now. We won’t
be talking much about these theory now. Coming to Scripts.
Move Current Working Directory
Move from current working
directory to any level up by just providing the numerical value at the end of
script while executing.
#! /bin/bash
LEVEL=$1
for ((i = 1; i <= LEVEL; i++))
do
CDIR=../$CDIR
done
cd $CDIR
echo "You are in: "$PWD
exec /bin/bash
Save
the above codes as “up.sh“, on your desktop. Make
it executable (chmod 755 up.sh). Run:
./up.sh 2 (will Move the current
working directory to two level up).
./up.sh 4 (will Move the current working directory to four level up).
./up.sh 4 (will Move the current working directory to four level up).
Use and Area of Application
In
larger scripts which contains folder inside folder inside… containing libraries, binaries, icons, executables, etc at different location,
You as a developer can implement this script to move to the desired location in
a very automated fashion.
Note: For is a loop in the above
script and it will continue to execute till the values are true for the loop.
Sample Output
[root@localhost /]# ./up.sh 2
You are in: /
[root@localhost /]# ./up.sh 4
You are in: /
[root@localhost /]#
Create a Random File or
Folder
Create a random file (folder)
with no chance of duplication.
echo "Hello $USER";
echo "$(uptime)" >> "$(date)".txt
echo "Your File is being saved to $(pwd)"
This is a Simple script but
it’s working is not that much simple.
1.
‘echo‘ : Prints everything written within the quotes.
2.
‘$‘ : Is a shell variable.
3.
‘>>‘ : The output is redirected to the output of date command
followed by txt extension.
We
know the output of date command is date, and time in hour, minute, second along with year. Hence we could get output on
an organised file name without the chance of filename duplication. It could be
very much useful when user needs the file created with time stamp for future reference.
Sample Output
Hello server
Your File is being saved to /home/server/Desktop
You can view the file which is
created on desktop with Today’s Date and current time.
13:51:52 up 3:54, 1 user, load average: 0.09, 0.12, 0.08
A
more detailed implementation of the above script is given below, which works on
the above principle and is very useful in gathering the network information of
a Linux server.
Script to Collect
Network Information
Gathers
network information on a Linux server. The script
is too large and it’s not possible to post the whole code and output of the
script here. So, it’s better you can download the script using below download
link and test it yourself.
Note: You might need to install lsb-core package and other
required packages and dependency. Apt or Yum the required packages.
Obviously you need to be root to run the script
because most of the commands used here are configured to be run as root.
Sample Output
The Network Configuration Info Written To network.20-07-13.info.txt. Please email this file to your_name@service_provider.com. ktop
You can change the above email
address in your script to get it being mailed to you. The Automatically
generated file can be viewed.
Script to Converts
UPPERCASE to lowercase
A
script that converts UPPERCASE to lowercase and redirects the output
to a text file “small.txt” which
can be modified as required.
echo -n "Enter File Name : "
read fileName
if [ ! -f $fileName ]; then
echo "Filename $fileName does not exists"
exit 1
fi
tr '[A-Z]' '[a-z]' < $fileName >> small.txt
This
above script can convert the case of a file of any length with a single click
from uppercase to lowercaseand vice-versa if required,
with little modification.
Sample Output
Enter File Name : a.txt
Initial File:
A
B
C
D
E
F
G
H
I
J
K
...
New
File (small.txt) output:
a
b
c
d
e
f
g
h
i
j
k
...
Simple Calculator
Program
clear
sum=0
i="y"
echo " Enter one no."
read n1
echo "Enter second no."
read n2
while [ $i = "y" ]
do
echo "1.Addition"
echo "2.Subtraction"
echo "3.Multiplication"
echo "4.Division"
echo "Enter your choice"
read ch
case $ch in
1)sum=`expr $n1 + $n2`
echo "Sum ="$sum;;
2)sum=`expr $n1 - $n2`
echo "Sub = "$sum;;
3)sum=`expr $n1 \* $n2`
echo "Mul = "$sum;;
4)sum=`expr $n1 / $n2`
echo "Div = "$sum;;
*)echo "Invalid choice";;
esac
echo "Do u want to continue (y/n)) ?"
read i
if [ $i != "y" ]
then
exit
fi
done
Sample Output
Enter one no.
12
Enter second no.
14
1.Addition
2.Subtraction
3.Multiplication
4.Division
Enter your choice
1
Sum =26
Do u want to continue (y/n)) ?
y
1.Addition
2.Subtraction
3.Multiplication
4.Division
Enter your choice
3
mul = 14812
Do u want to continue (y/n)) ?
n
So did you saw how
easy it was to create a powerful program as calculations such a simple way. Its’
not the end. We will be coming up with at least one more article of this
series, covering broad perspective from administration view.
That’s all for now. Being the reader and the best critic don’t
forget to tell us how much and what you enjoyed in this article and what you
want to see in the future article. Any question is highly welcome in comment.
Till then stay healthy, safe and tuned. Like and Share us and help us spread.
