tr - translate or delete characters.
Convert specific character to another:
tr "-" "_"
Convert lower case to upper case:
tr [a-z] [A-Z]
Convert white-space to tabs:
tr " " "\t"
Convert multiple continuous spaces with a single space:
tr -s " "
Delete specific characters:
tr -d 'a'
Delete all numbers:
tr -d [:digit:]
Delete all the letters:
tr -d [:alpha:]