I actually had (!~) initially but I read on a webpage that it's better to use "ne".

When comparing against a constant strings, it's more efficient to avoid regexps.

$var eq 'abc'
$var ne 'abc'
$var1 eq $var2
$var1 ne $var2
[download]

are faster and simpler than

$var =~ /^abc\z/
$var !~ /^abc\z/
$var1 =~ /^\Q$var2\z/
$var1 !~ /^\Q$var2\z/
[download]

I'll study the different not equals soon.

$var ne /regexp/
means
$var ne ($_ =~ /regexp/)

• When matching against a regexp, use a match operator (=~ or !~).
• When comparing strings, use a string comparison operator (eq, ne, lt, gt, le, ge or cmp).
• When comparing numbers, use a numerical comparison operator (==, !=, <, >, <=, >= or <=>).