tr command in Unix/Linux with examples

The tr command in UNIX is a command line utility for translating or deleting characters. It supports a range of transformations including uppercase to lowercase, squeezing repeating characters, deleting specific characters and basic find and replace. It can be used with UNIX pipes to support more complex translation. tr stands for translate.

Syntax :

$ tr [OPTION] SET1 [SET2]

Options

-c : complements the set of characters in string.i.e., operations apply to characters not in the given set
-d : delete characters in the first set from the output.
-s : replaces repeated characters listed in the set1 with single occurrence
-t : truncates set1

Sample Commands

1. How to convert lower case to upper case

To convert from lower case to upper case the predefined sets in tr can be used.

$cat greekfile

Output:

WELCOME TO
LPICentral

$cat greekfile | tr “[a-z]” “[A-Z]”

Output:

WELCOME TO
LPICentral

or

$cat lpifile | tr “[:lower:]” “[:upper:]”

Output:

WELCOME TO
LPICENTRAL

2. How to translate white-space to tabs

The following command will translate all the white-space to tabs

$ echo "Welcome To LPICentral" | tr [:space:] '\t'

Output:

Welcome    To    LPICentral 

3. How to translate braces into parenthesis

You can also translate from and to a file. In this example we will translate braces in a file with parenthesis.

$cat greekfile

Output:

 {WELCOME TO}
LPICentral
$ tr '{}' '()'   newfile.txt

Output:

(WELCOME TO)
LPICentral

The above command will read each character from “lpifile.txt”, translate if it is a brace, and write the output in “newfile.txt”.

4. How to use squeeze repetition of characters using -s

To squeeze repeat occurrences of characters specified in a set use the -s option. This removes repeated instances of a character.
OR we can say that,you can convert multiple continuous spaces with a single space

$ echo "Welcome    To    LPICentral" | tr -s [:space:] ' '

Output:

Welcome To LPICentral

5. How to delete specified characters using -d option

To delete specific characters use the -d option.This option deletes characters in the first set specified.

$ echo "Welcome To LPICentral" | tr -d 'w'

Output:

elcome To LPICentral

6. To remove all the digits from the string, use

$ echo "my ID is 73535" | tr -d [:digit:]

Output:

my ID is

7. How to complement the sets using -c option

You can complement the SET1 using -c option. For example, to remove all characters except digits, you can use the following.

$ echo "my ID is 73535" | tr -cd [:digit:]

Output:

73535

Or

$ echo “unix” | tr –c “u” “a”

Output:

Uaaa