use strict;

my @FILES=("ABC","DEF","GHI","JKL","MNO","PQR","STU");

my %have_file = map { $_ => 1 } @FILES;

if ($have_file{ABC} and $have_file{GHI} and $have_file{MNO} ) {
    # do something
}
else {
    # do something else
}
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