The Linux tr Command

What is tr

tr (translate) changes or removes characters in text that comes from standard input. It does not take file names, so you use it with a pipe or with <.

Syntax

tr [OPTION] SET1 [SET2]

Options:

• -c complements SET1, which means it works on all the characters not in the set.
• -d deletes the characters in SET1.
• -s squeezes repeated characters in SET1 into a single one.
• -t truncates SET1 to the length of SET2.

Read the manual:

man tr

Example 1: Change the case

Lower case to upper case:

echo "Hi, I am a technical writer" | tr 'a-z' 'A-Z'

Upper case to lower case:

echo "HI, WELCOME TO THE KNOWLEDGE BASE" | tr 'A-Z' 'a-z'

You can also use the classes: tr '[:lower:]' '[:upper:]'.

Example 2: Save the result in a file

echo "HI, WELCOME TO THE KNOWLEDGE BASE" | tr ' ' '\n' > words.txt

This replaces each space with a new line and writes the result to words.txt.

Example 3: Replace one character

Replace a comma with a semicolon:

echo "one,two,three" | tr ',' ';'

Output: one;two;three

Example 4: Squeeze repeated characters

echo "hello     world" | tr -s ' '

Output: hello world

Example 5: Delete characters

Delete a specific character:

echo "hello world" | tr -d 'l'

Output: heo word

Delete all digits:

echo "abc123def456" | tr -d '0-9'

Output: abcdef

Example 6: Use the complement

Keep only the digits and delete everything else:

echo "abc123def456" | tr -cd '0-9'

Output: 123456

Other uses

Remove Windows line endings from a file:

tr -d '\r' < windows.txt > unix.txt

Make a random password of 16 letters and digits:

tr -dc 'A-Za-z0-9' < /dev/urandom | head -c 16; echo

Quick recap

• tr 'a-z' 'A-Z' changes case, tr -d deletes, tr -s squeezes, tr -c complements.
• tr reads only from standard input.