String replacement (${var/old/new}) in Bash Scripting

Introduction

You use string replacement to change parts of text stored in a variable quickly without extra tools.

Fix a typo in a word inside a variable.

Change a file extension in a filename stored in a variable.

Replace a word in a sentence stored in a variable.

Update a URL or path stored in a variable.

Modify a configuration value inside a string.

Syntax

Bash Scripting

${variable/old/new}

This replaces the first occurrence of 'old' with 'new' in the variable's value.

To replace all occurrences, use ${variable//old/new} with double slashes.

Examples

Replaces 'world' with 'universe' in the variable 'text'.

Bash Scripting

text="hello world"
echo "${text/world/universe}"

Changes the file extension from 'txt' to 'pdf'.

Bash Scripting

filename="report.txt"
echo "${filename/txt/pdf}"

Replaces only the first 'fish' with 'cat'.

Bash Scripting

sentence="one fish two fish"
echo "${sentence/fish/cat}"

Replaces all 'fish' with 'cat' using double slashes.

Bash Scripting

sentence="one fish two fish"
echo "${sentence//fish/cat}"

Sample Program

This script shows how to replace the first and all occurrences of 'apples' with 'oranges' in a string variable.

Bash Scripting

#!/bin/bash
text="I love apples and apples are tasty"
# Replace first 'apples' with 'oranges'
new_text="${text/apples/oranges}"
echo "$new_text"
# Replace all 'apples' with 'oranges'
all_replaced="${text//apples/oranges}"
echo "$all_replaced"

Important Notes

String replacement does not change the original variable unless you assign it back.

It works only on variables, not on command output directly.

Use double slashes (//) to replace all matches, single slash (/) for the first match only.

Summary

Use ${var/old/new} to replace the first match of 'old' with 'new' in a variable.

Use ${var//old/new} to replace all matches.

This is a quick way to edit text inside variables without extra commands.