Since [a-z]+ doesn't match hyphens, I'm guessing you are doing

# Matches if the string contains a sequence
# of 1 or more lowercase letters
$str =~ /[a-z]+/
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when you want to do

# Matches if the string consists entirely of
# a sequence of 1 or more lowercase letters,
# optionally followed by a newline
$str =~ /^[a-z]+$/
[download]

or

# Matches if the string consists entirely of
# a sequence of 1 or more lowercase letters
$str =~ /^[a-z]+\z/
[download]