Bash for Loop in Linux

Definitions

Loops are a set of commands that the computer repeats until a certain condition is met. They can be broken before that condition is met with a specific command. They are used for counting, searching for information, or populating data structures.

In computer science there are two main loops: the for loop and the while loop.

for loop:

In computer science, a for loop is a programming language statement which allows code to be repeatedly executed. It is classified as an iteration statement. Unlike many other kinds of loops, such as the while loop, the for loop is often distinguished by an explicit loop counter or loop variable.

while loop:

In most computer programming languages, a while loop is a control flow statement that allows code to be executed repeatedly based on a given boolean condition. The while loop can be thought of as a repeating if statement.

With that understood, let's start with the Bash for loop article.

How to use bash for loop

In Bash there are two ways to implement a for loop:

1. Instruct for to act on a predefined list of elements, using the for … in statement.
2. Use C syntax: for (( exp1, exp2, exp3 )).

Simple examples of each:

Using for ... in statement

for i in 1 2 3 4
do
    echo "Number $i"
done

Using for ((exp1, exp2, exp3)) statement

for (( i=1; i<=4; i++))
do
    echo "Number $i"
done

The result is the same in both cases:

Number 1
Number 2
Number 3
Number 4

Examples

Counting:

#!/bin/bash
for i in {1..25}
do
    echo $i
done

Or:

#!/bin/bash
for ((i=1;i<=25;i+=1))
do
    echo $i
done

Counting in n steps:

#!/bin/bash
for i in {0..25..5}
do
    echo $i
done

This counts in steps of 5.

Counting backwards:

#!/bin/bash
for i in {25..0..-5}
do
    echo $i
done

Acting on files:

One of the best uses for a for loop in Bash is working with files:

for file in ~/*.md
do
    echo $file
done

That example lists all files with .md extension — equivalent to ls *.md.

Break and continue in the for loop

Sometimes you want to stop the loop before it finishes. For example, when you are waiting for a condition to be met:

for i in [series]
do
    command1
    command2
    if (condition)
    then
        break
    fi
    command3
done

With break you stop the loop completely. With continue, you skip to the next value in the series without running the remaining commands in that iteration:

for i in [series]
do
    command1
    command2
    if (condition)
        continue
    fi
    command3
done

One-liner bash for loop

When working in the command line, you often write for loops as one-liners rather than inside a script.

Using one-liners with counters:

for i in {1..3}; do echo 'hello'; done

Or:

for ((i=1;i<=3;i++)); do echo "hello"; done

Even numbers up to 30:

for ((i=0;i<=30;i+=2)); do echo "$i is even"; done

Copy all PDF files to a backup directory:

for i in *.pdf; do cp $i /backup/; done

Add a .bak extension to all .txt files:

for i in *.txt; do mv $i $(basename $i .txt).bak; done

Last edit on: June 2nd, 2019

Last updated on: June 26, 2026

By: Guillermo Garron