Linux tr Command

The tr (translate) command is a Linux utility that allows you to perform various transformations on text input. Whether you need to change case, remove repeating characters, delete characters, set complements, or replace specific characters, tr can handle it all. In this article, we'll explore the various options available with the tr command and show you how to use them to transform text.

Syntax

The basic syntax of the tr command is as follows ?

tr [OPTIONS] SET1 [SET2]

Where ?

• SET1 is a set of characters to be replaced by the corresponding characters in SET2.

• SET2 is a set of characters that replaces the corresponding characters in SET1.

• OPTIONS include flags like -d (delete), -s (squeeze), -c (complement).

The tr command reads from standard input and writes to standard output. Characters in SET1 and SET2 can be specified as individual characters, ranges like [a-z], or character classes like [:upper:].

Basic example replacing one character with another ?

$ echo "Hello World" | tr 'H' 'Y'

Yello World

Change Character Case

The tr command can change the case of input text in several ways.

Using Character Ranges

Convert all uppercase letters to lowercase using ranges ?

$ echo "Hello World" | tr '[A-Z]' '[a-z]'

hello world

Using Character Classes

Use predefined character classes for case conversion ?

$ echo "HELLO WORLD" | tr '[:upper:]' '[:lower:]'

hello world

Similarly, convert lowercase to uppercase ?

$ echo "hello world" | tr '[:lower:]' '[:upper:]'

HELLO WORLD

Remove Repeated Characters

The -s (squeeze) option compresses repeated characters into a single instance. This is useful for cleaning up text with multiple consecutive spaces or other repeated characters.

$ echo "Hello    World" | tr -s ' '

Hello World

Replace multiple spaces with a single tab ?

$ echo "Hello    World" | tr -s ' ' '\t'

Hello	World

Delete Characters

Use the -d option to delete specific characters from input.

Delete Specific Characters

$ echo "Hello World" | tr -d 'e'

Hllo World

Delete Character Classes

Remove all digits from text ?

$ echo "Hello 123 World" | tr -d '[:digit:]'

Hello  World

Delete with Complement

Use the -c option to complement the character set, keeping only the specified characters ?

$ echo "Hello 123 World" | tr -cd '[:digit:]'

123

Common Use Cases

Convert Spaces to Newlines

Split words into separate lines ?

$ echo "Hello World Linux" | tr ' ' '<br>'

Hello
World
Linux

Remove Newlines

Convert multiple lines into a single line ?

$ printf "Hello\nWorld\nLinux" | tr '<br>' ' '

Hello World Linux

Character Translation Table

Advanced Options

Conclusion

The tr command is a versatile text transformation utility that excels at character-level operations like case conversion, character deletion, and text cleanup. It's particularly useful for data preprocessing, file formatting, and stream processing tasks. Whether you're cleaning data files or transforming text output, tr provides a simple yet powerful solution for character-based text manipulation.