tr for character transformation in Bash Scripting

Introduction

The tr command changes or deletes characters in text. It helps fix or clean text quickly.

You want to change all lowercase letters to uppercase in a file.

You need to remove all digits from a text stream.

You want to replace spaces with underscores in a filename.

You want to delete all punctuation marks from a sentence.

You want to squeeze repeated characters into one (like multiple spaces into one).

Syntax

Bash Scripting

tr [options] SET1 [SET2]

SET1 is the set of characters to replace or delete.

If SET2 is given, characters in SET1 are replaced by corresponding characters in SET2.

Examples

Converts all lowercase letters to uppercase.

Bash Scripting

echo "hello" | tr 'a-z' 'A-Z'

Deletes all digits from the input.

Bash Scripting

echo "123abc" | tr -d '0-9'

Replaces spaces with underscores.

Bash Scripting

echo "hello  world" | tr ' ' '_'

Sample Program

This script takes a string, changes all lowercase letters to uppercase using tr, and prints the result.

Bash Scripting

#!/bin/bash

# Convert lowercase to uppercase
input="hello world"
output=$(echo "$input" | tr 'a-z' 'A-Z')
echo "$output"

Important Notes

tr works on standard input and outputs to standard output, so use pipes or redirection.

The -d option deletes characters from the input.

The -s option squeezes repeated characters into one.

Summary

tr changes or deletes characters in text streams.

Use it to convert cases, delete unwanted characters, or replace characters.

It reads from input and writes transformed text to output.