tr -- translate or delete characters

http://linux.about.com/library/cmd/blcmdl1_tr.htm

NAME

tr - translate or delete characters  

SYNOPSIS

tr [OPTION]... SET1 [SET2]  

DESCRIPTION

Translate, squeeze, and/or delete characters from standard input, writing to standard output.

-c, --complement

first complement SET1

-d, --delete

delete characters in SET1, do not translate