tr Command Cheat Sheet

tr (translate) copies standard input to standard output, performing substitution or deletion of selected characters. Input Source: tr ONLY processes Stdin. It does not accept filenames as arguments (use < or pipes).

Synopsis

tr [OPTION]... SET1 [SET2]

Basic Translation

Lowercase to Uppercase

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

Replace Characters

Replace spaces with underscores.

echo "Hello World" | tr ' ' '_'
# Output: Hello_World

Swap Characters

echo "{ok}" | tr '{}' '()'
# Output: (ok)

Deletion (-d)

Delete specific characters.

# Remove all digits
echo "User123" | tr -d '0-9'
# Output: User

# Remove newlines (join lines)
cat file.txt | tr -d '\n'

Squeeze Repeats (-s)

Replace a sequence of repeated characters with a single occurrence.

# Fix extra spaces
echo "Too    many    spaces" | tr -s ' '
# Output: Too many spaces

Delete & Squeeze

Delete digits AND squeeze spaces.

echo "Item   123   Price" | tr -d '0-9' | tr -s ' '

Complement (-c)

Operate on everything except the specified set.

# Keep only alphanumeric and newlines (delete everything else)
cat file.txt | tr -cd '[:alnum:]\n'

ROT13 Encryption (Caesar Cipher)

Shift characters by 13 positions.

alias rot13="tr 'A-Za-z' 'N-ZA-Mn-za-m'"
echo "secret" | rot13
# Output: frperg

Character Classes

[:alnum:]: Letters and digits
[:alpha:]: Letters
[:digit:]: Digits
[:punct:]: Punctuation
[:space:]: Whitespace (tab, newline, vertical tab, form feed, return, space)
[:upper:]: Uppercase
[:lower:]: Lowercase

# Remove all punctuation
cat text.txt | tr -d '[:punct:]'