#!/usr/bin/perl -w
use strict;
#                0      0     1     0      1
my @words = qw, eLBow ElBow elBoW eLbow elboW,;
# I want to match all words elbow
# whose W is capital, and e and o e are in lower case
# and but l and B can be either case
# There are two ways to do it
for(@words)
{
    printf "%s\n",$_ if /e(L|l)(B|b)oW/;
}

##or using Extended Regular Expressions

for(@words)
{
    printf "%s\n",$_
    if /e(?i-:lb)oW/;
}
__END__
# the output
elBoW
elboW
elBoW
elboW