Bash — While Loops

Basic while loop

#!/bin/bash

count=0
while [ $count -lt 5 ]; do
    echo "$count"
    ((count++))
done

Reading file line by line

#!/bin/bash

while IFS= read -r line; do
    echo "$line"
done < file.txt

Reading user input

#!/bin/bash

while true; do
    read -p "Enter command (quit to exit): " cmd
    [ "$cmd" = "quit" ] && break
    echo "You entered: $cmd"
done

Until loop

#!/bin/bash

count=0
until [ $count -ge 5 ]; do
    echo "$count"
    ((count++))
done

break and continue

#!/bin/bash

# break
for i in {1..10}; do
    [ $i -eq 5 ] && break
    echo "$i"
done

# continue
for i in {1..10}; do
    [ $((i % 2)) -eq 0 ] && continue
    echo "$i"
done

Infinite loop

#!/bin/bash

while true; do
    echo "Running..."
    sleep 1
    # Use Ctrl+C to stop
done

Mini Practice

Write Bash code that:

1. Uses a while loop to read user input
2. Reads a file line by line
3. Uses until for a countdown
4. Uses break and continue

Up Next

In the next lesson, you'll learn about Functions — defining and using functions.