tr — character translation

The tr command can be used to translate, squeeze and delete character sequences. See man tr and IEEE Std 1003.1-2017-tr for the full specification.

tr operates in a number of modes, depending upon the invocation:

Deleting characters
To delete all occurrences of certain characters, use tr -d asdf.
Deleting repeated characters
To replace repeated characters with a single character ('squeeze'), use tr -s asdf.
Transliterating characters
To replace all 'a' characters with '1', all 'b' with '2' and all 'c' with '3', use tr abc 123.

Certain special forms are allowed for the arguments. a-z expands to all characters from 'a' to 'z', \t represents a tab and so on. See the documentation for a full list.