I was looking for a solution in the Q&A section that would remove the elements in @B from @A, returning @C. I happened upon the exact question as mine, however one of the answers supplied (dragonchild's) was the opposite of what was wanted and I think whoever is in charge of this should substitute it with the following:

#!perl! -w
use strict;
use Data::Dumper;

my @A = ( 'yahoo.com', 'altavista.com', 'yahoo.com/index.html' );
my @B = ( 'yahoo.com', 'webcrawler.com' );

# The task: make a @C such that @C = ( 'altavista.com' )

# dragonchild's solution:
my @C = map { my $x = $_; grep { $x =~ /\Q$_/i } @B } @A;
# produces ( 'yahoo.com', 'yahoo.com' )

# proper solution:
my @D = grep { 
    my $x = $_;
    my @matches = grep { $x =~ /\Q$_/i } @B;
    ! @matches
} @A;

print Dumper [ \@A, \@B, \@C, \@D ];
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