tr

Translate, squeeze, and/or delete characters

Description

The tr command is used to translate, squeeze, or delete characters from standard input. it can transform one set of characters into another and is frequently used to write elegant, powerful one-liners.

Syntax

tr [options] [parameters]

Options

-c, --complement: Replace all characters not in the first character set;
-d, --delete: Delete all characters in the first character set;
-s, --squeeze-repeats: Replace sequences of repeated characters with a single instance of that character;
-t, --truncate-set1: Truncate the first set to the length of the second set before translation.

Parameters

• Set1: Specifies the original character set to be translated or deleted. When performing translation, Set2 must be specified as the target set. Set2 is not needed for deletion operations.
• Set2: Specifies the target character set for translation.

Examples

Convert input characters from uppercase to lowercase:

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

'A-Z' and 'a-z' are sets. Sets can be custom-defined, for example: 'ABD-}', 'bB.,', 'a-de-h', 'a-c0-9'. Sets can also include escape sequences like '\n', '\t', and other ASCII characters.

Delete characters using tr:

echo "hello 123 world 456" | tr -d '0-9'
hello  world 

Convert tabs to spaces:

cat text | tr '\t' ' '

Set complement: delete all characters from the input text that are NOT in the specified set:

echo aa.,a 1 b#$bb 2 c*/cc 3 ddd 4 | tr -d -c '0-9 \n'
 1  2  3  4

In this example, the complement set contains digits 0-9, spaces, and the newline character \n. Therefore, these are not deleted, while all other characters are removed.

Squeeze characters using tr: replace repeated characters with a single character:

echo "thissss is      a text linnnnnnne." | tr -s ' sn'
this is a text line.

Using tr for simple addition:

echo 1 2 3 4 5 6 7 8 9 | xargs -n1 | echo $[ $(tr '\n' '+') 0 ]

Remove '^M' (carriage return) characters caused by Windows files:

cat file | tr -s "\r" "\n" > new_file
# OR
cat file | tr -d "\r" > new_file

Character classes available in tr:

[:alnum:]: Letters and digits
[:alpha:]: Letters
[:cntrl:]: Control (non-printing) characters
[:digit:]: Digits
[:graph:]: Graphic characters
[:lower:]: Lowercase letters
[:print:]: Printable characters
[:punct:]: Punctuation marks
[:space:]: Whitespace characters
[:upper:]: Uppercase letters
[:xdigit:]: Hexadecimal digits

Usage:

tr '[:lower:]' '[:upper:]'