tr (translate characters) in Linux CLI - Commands & Configuration

Introduction

Sometimes you need to change or remove certain characters in text. The tr command helps you replace or delete characters quickly in Linux command line.

When you want to convert all lowercase letters in a file to uppercase.

When you need to remove all digits from a text stream.

When you want to replace spaces with underscores in filenames.

When cleaning up input by deleting unwanted characters like punctuation.

When preparing data by translating characters before processing.

Commands

This command converts all lowercase letters in the phrase 'hello world' to uppercase letters.

Terminal

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

Expected Output

HELLO WORLD

This command deletes all digits from the string 'user1234data', leaving only letters.

Terminal

echo "user1234data" | tr -d '0-9'

Expected Output

userdata

→

-d - Deletes characters specified in the set.

This command replaces all spaces in the filename with underscores to make it easier to handle in scripts.

Terminal

echo "file name with spaces.txt" | tr ' ' '_'

Expected Output

file_name_with_spaces.txt

Key Concept

If you remember nothing else from tr, remember: it replaces or deletes characters from input streams one by one.

Common Mistakes

Using tr with strings of different lengths for source and target sets.

tr expects the source and target sets to be the same length for translation; otherwise, it may produce unexpected results.

Make sure the sets you provide to tr have the same number of characters when translating.

Trying to use tr to replace words or multiple characters at once.

tr works on single characters only, not strings or words.

Use other tools like sed or awk for replacing words or patterns.

Not quoting character sets, causing shell expansion issues.

Without quotes, the shell might interpret characters like * or ? before tr runs.

Always quote character sets to prevent shell expansion.

Summary

Use tr to translate or delete characters in text streams.

The -d flag deletes specified characters instead of replacing them.

Always ensure source and target character sets are the same length for translation.