make 'tr' (or something like it) a bash builtin ?

[Mike Frysinger]

if i'm simply unaware of such bash features, please feel free to yell at me :)

when working on misc bash scripts, i semi-frequently find the need to do some 
sort of string processing along the lines of say changing a string to all 
upper case or lower case ... if 'tr' was a bash builtin, then that'd work 
with some `echo | tr` magic, but it something like 
${foo//[[:lower:]]/[[:upper:]]} would be nice
-mike