regexDrop = /String01|String2|\bEND\b/i        #END\n/i
a = "the long END not begin of line"
b = "ENd"              # <@><<  need  this one
c = "END MORE WORDs"
d ="  EnD"            # <@><<  need  this one
 
if a =~ regexDrop then  puts "a__Match: " + a     else  puts 'a_'     end
if b =~ regexDrop then  puts "b__Match: " + b     else  puts 'b_'     end
if c =~ regexDrop then  puts "c__Match: " + c     else  puts 'c_'     end
if d =~ regexDrop then  puts "d__Match: " + d     else  puts 'd_'     end

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