Multiple comparison of string variable in perl -

i'm trying make kind of bash-like case statement in perl using if operator.

my $var = shift @argv; print "err\n" if (!$var || ($var ne "one") || ($var ne "two"));

the problem is, 'if' statement not work expected. example, if pass input 'one' or 'two' prints 'err', but, if swap 'ne' 'eq' script works correctly.

perl version 5.16.3 linux

not($p && $q) == (!$p || !$q) not($p || $q) == (!$p && !$q)

if allowed values "one" or "two", write:

print "err\n"   unless defined $var      , $var eq "one" || $var eq "two";

if want use ne, then:

print "err\n"   if ! defined $var   or $var ne "one" && $var ne "two";

these 2 forms equivalent. if have more 2 allowed strings, gets easier , more efficient using hash:

my %allowed; @allowed{"one", "two"} = ();  print "err\n" unless defined $var , exists $allowed{$var};

the problem code was: when or-ing multiple conditions together, sufficient 1 sub-condition true whole condition true.

given undef or other false value, !$var true.
given string "one", $var ne "two" true.
given other string, $var ne "one" true.

therefore, ($var ne "one") || ($var ne "two") true.

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