Loops are very useful for doing repetitive tasks for any programming language. For loops are also available for bash scripting. In this article we will learn about uses of for loops with useful examples.
Syntax:
do
// commands to execute
done
In above syntax PARAM1, PARAM2 and PARAM3 are parameters passed as an arguments. These parameters can be a number string or file names. For loop will be executed 3 times as per numbers of parameters passed in above syntax. VARIABLE is a variable which is initialized one by one using parameter values.
Examples of For Loop in Bash Script
To define number of number of iteration’s for a loop, we simply pass numbers as an argument for variable.
fori in1 2 3 4 5 6 do echo "$i " done
We can also define range in place of writing each number on latest version of bash. To define a range we use curly braces like {STARTNUMBER..ENDNUMBER}.
fori in {1..6 } do echo "$i " done
We can also pass string values as parameters for defining number of iterations and pass as argument
fori inSUN MON TUE WED THU FRI SAT do echo "This is $i " done
We can also pass all the file names as arguments to pass to loop.
fori in* do echo "This file is $i " done
Creating C Like For Loop in Bash Script
We can also create C like for loops inside a shell script
Syntax:
do
// commands to execute
done
Where EXPR1 is used for initialization, EXPR2 is used for condition and EXPR3 is used for increment/decrement of variable values.
For example to execute a loop 10 times we can simply write for loops like
for ((i=1; i<=10; i++)) do echo "$i" done