tr(1)
NAME
tr - translate character codes
SYNOPSIS
tr [-cds] [string1] [string2]
OPTIONS
-c Complement the set of characters in string1
-d Delete all characters specified in string1
-s Squeeze all runs of characters in string1 to one character
EXAMPLES
tr 'A-Z' 'a-z' <x >y
# Convert upper case to lower case
tr -d '0123456789' <f1 >f2
# Delete all digits from f1
DESCRIPTION
Tr performs simple character translation. When no flag is specified,
each character in string1 is mapped onto the corresponding character in
string2 .
There are two types of tr out there, one that requires [ and ] for
character classes, and one that does not. Here is what the example above
would look like for a tr that needs the brackets:
tr '[A-Z]' '[a-z]' <x >y
Use [ and ] if you want to be portable, because a tr that doesn't need
them will still accept the syntax and mindlessly translate [ into [ and ]
into ].