How to Use Loops in Linux Shell Scripts 📂Programing

How to Use Loops in Linux Shell Scripts

for loops

List the items to iterate over directly after in.

Code:

for i in apple banana cherry; do
    echo "Fruit: $i"
done

Output:

Fruit: apple
Fruit: banana
Fruit: cherry

You can use the seq command to specify a range of numbers.

Code:

for i in $(seq 1 5); do
    echo "Number: $i"
done

Output:

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Use the {} syntax to list multiple items on a single line.

Code:

for i in {A..E}; do
    echo "Letter: $i"
done

for i in {1..5}; do
    echo "Number: $i"
done

Output:

Letter: A
Letter: B
Letter: C
Letter: D
Letter: E

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Note that a single space is required after [ and before ].

Code:

double=1
while [ $double -le 500 ]; do
    echo "double is $double"
    double=$(( double + double ))
done

Output:

double is 1
double is 2
double is 4
double is 8
double is 16
double is 32
double is 64
double is 128
double is 256