tr / col / expand

tr [options] set1 [set2]
expand [options] [file...]
unexpand [options] [file...]

Command / Option	Description
tr 'abc' 'ABC'	Translates each character in set1 to the corresponding character in set2.
tr '[:lower:]' '[:upper:]'	Converts all lowercase letters to uppercase.
tr '[:upper:]' '[:lower:]'	Converts all uppercase letters to lowercase.
tr -d 'set'	Deletes all characters in the specified set.
tr -s 'set'	Squeezes consecutive repeated characters in the set into a single character.
tr -c 'set1' 'set2'	Translates the complement of set1 (characters not in set1) to set2.
tr '\r' '\n'	Used to remove the \r from Windows line endings (\r\n).
expand file	Converts tabs to 8 spaces.
expand -t N file	Converts tabs to N spaces.
unexpand file	Converts leading spaces to tabs.

The following examples demonstrate how each command works.

# Example input text:
# "hello world"       → convert to uppercase
# "my file name.txt"  → replace spaces
# "abc123def456"      → delete characters
# "too    many   spaces" → squeeze repeated characters

Converts all lowercase letters to uppercase.

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

Replaces spaces with underscores (useful for normalizing filenames).

echo "my file name.txt" | tr ' ' '_'
my_file_name.txt

Uses -d to delete specified characters. This example removes all alphabetic characters, leaving only digits.

echo "abc123def456" | tr -d '[:alpha:]'
123456

Uses -s to squeeze consecutive repeated characters into one.

echo "too    many   spaces" | tr -s ' '
too many spaces

Combines -s with cut to extract fields from data with irregular spacing.

echo "  alice  30  Tokyo  " | tr -s ' ' | cut -d' ' -f2-
alice 30 Tokyo

Uses -c (complement) to replace all non-alphanumeric characters with spaces.

echo "hello, world! 123" | tr -c '[:alnum:]\n' ' '
hello  world  123

Removes \r from Windows line endings (\r\n) to convert to Unix format.

tr -d '\r' < windows_file.txt > unix_file.txt

Uses expand -t N to convert tabs to N spaces.

printf "name\tage\ncity\tcode\n" | expand -t 8
name    age
city    code

tr does not accept filenames as arguments — it only reads from standard input. To process a file, redirect it using tr < file.

tr is commonly used to convert line endings when working with Windows text files on Linux (\r\n → \n). For more advanced text transformation, see also sed.