Perl doesn't have a single false value, it has "falsey" values. Then it has defined, which turns everything but undef into a "truthy" value.

For example:

print(( 0             ) ? qq{not false\n} : qq{false\n});# false
print(( defined 0     ) ? qq{not false\n} : qq{false\n});# not false
print(( ''            ) ? qq{not false\n} : qq{false\n});# false
print(( defined ''    ) ? qq{not false\n} : qq{false\n});# not false
print(( undef         ) ? qq{not false\n} : qq{false\n});# false
print(( defined undef ) ? qq{not false\n} : qq{false\n});# false
print(( ' '           ) ? qq{not false\n} : qq{false\n});# not false
print(( -1            ) ? qq{not false\n} : qq{false\n});# not false
print(( ()            ) ? qq{not false\n} : qq{false\n});# false
print(( []            ) ? qq{not false\n} : qq{false\n});# not false
print(( {}            ) ? qq{not false\n} : qq{false\n});# not false
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Which leads me to point out that Perl behaves correctly, even when faced with "No Output For This Line!" and '"phantom" version of false'.

print(( "a" =~ m/a/ ) ? qq{not false\n} : qq{false\n});  # "not false"
print(( "a" =~ m/b/ ) ? qq{not false\n} : qq{false\n});  # "false"
print(( "a" eq "a" )  ? qq{not false\n} : qq{false\n});  # "not false"
print(( "a" eq "b" )  ? qq{not false\n} : qq{false\n});  # "false"
print(( "a" !~ m/a/ ) ? qq{not false\n} : qq{false\n});  # "false"
print(( "a" !~ m/b/ ) ? qq{not false\n} : qq{false\n});  # "not false"
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