The tr command is a UNIX command-line utility for translating or deleting characters

basic form
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tr set1 set2		#translate set1 into set2
tr -d 'W'		#delete char W, and delete is a special case, so use option d
tr 'a-z' 'A-Z'		#range translate
tr -s ' '		#compress spaces into 1 space
tr -d -c '0-9'		#remove un-digits (keep digits). you can think this way: -d is delete, why add -c in? it is a reverese of it, still delete but delete un-digits
tr -d '[:punct:]'	#remove punctation chars