tr flags & options

`-d`, `--delete`

Delete characters in SET1, do not translate.

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

tr -d '\r' < file.txt

Replace each sequence of repeated characters with a single occurrence.

echo "aabbcc" | tr -s 'a-z'

tr -s ' ' < file.txt

Use the complement of SET1.

echo "hello 123" | tr -cd '0-9'

tr -cd '[:print:]\n' < file.txt

Translate between uppercase and lowercase.

echo "hello" | tr '[:lower:]' '[:upper:]'

echo "HELLO" | tr '[:upper:]' '[:lower:]'

Match all digit characters.

echo "abc123def" | tr -d '[:digit:]'

echo "abc123" | tr -cd '[:digit:]'