In Linux, all tasks from execution of services to loading and unloading of modules are carried out by programs and all programs need to be executed. You use the commands to access all the basic features of kernel. Shell scripting is a way to automate such tasks, and bash is one of the language, that has capabilities enough to be called as scripting as well as a language that can be used for programming on the POSIX platform, for small tasks. Bash Scripting While Loop
Using While Loop:
Create a bash file with the name, ‘while_loop.sh’, to know the use of while loop. In the example, while loop will iterate for 5 times. The value of count variable will increment by 1 in each step. When the value of count variable will 5 then the while loop will terminate.
#!/bin/bash
valid=true
count=1
while [ $valid ]
do
echo $count
if [ $count -eq 5 ];
then
break
fi
((count++))
done
Run the file with bash command.
$ bash while_loop.sh
Example-2: Using break statement for conditional exit
break statement is used to exit from the loop early based on a particular condition. Create a new bash file named while_loop2.sh with the following code.
#!/bin/bash
n=1
while [ $n -le 8 ]
do
echo "Runnning $n time"
(( n++ ))
done
Run the file with bash command.
$ bash while_loop2.sh
Example-3: Using continue statement to omit particular step
Create a new bash file named bash while_loop3.sh with the following code.
#!/bin/bash
n=0
while [ $n -le 5 ]
do
(( n++ ))
if [ $n == 3 ]
then
continue
fi
echo "Position: $n"
done
Run the file with bash command.
$ bash while_loop3.sh
In this example, the loop will iterate for 5 times but it will not print all 5 positions.
When the loop will iterate for 3rd times then continue statement will be executed and the loop will go for the next
iteration without printing the text of 3rd position. The following output will appear after executing the script.
Example-4: Creating infinite loop
Sometimes, it is required to declare infinite loop for various programming purposes. Create a new bash file named while_loop4.sh and test the code of infinite loop.
n=1
while :
do
printf "The current value of n=$n\n"
if [ $n == 3 ]
then
echo "good"
elif [ $n == 5 ]
then
echo "bad"
elif [ $n == 7 ]
then
echo "ugly"
elif [ $n == 10 ]
then
exit 0
fi
((n++))
done
Run the file with bash command.
$ bash while_loop4.sh
No termination condition is set for the loop in this example. This type of loop is called infinite loop. Here, exit statement is used to quit from the infinite loop. So, this loop will iterated for 10 times and when the iteration value become equal to 10 then exit statement will execute for exiting from the infinite loop.
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