Re: This is why Perl is so frustrating

if (($file ne ".") or ($file ne ".."))
[download]

Will always be true, because no single value of $file can ever match both "." and "..". So yes, you are missing a fundamental aspect of logical operations.

Namely: For a given A != B, (!A or !B) == !(A && B), which will always be true for any single value.

Update:
Perhaps you should spend some time reading this article.

Comment on Re: This is why Perl is so frustrating Select or Download Code

Replies are listed 'Best First'.
Re^2: This is why Perl is so frustrating by ikegami (Patriarch) on Jul 29, 2009 at 23:03 UTC
Namely: For a given A != B, (!A or !B) == !(A && B), which will always be true for any single value. ow. You attached two conditions to `(!A or !B) == !(A && B)`, but it's always true. You refer some non-existent "single value" because you meant to talk about `(V != A) or (V != B)`. I believe you meant: `(A or B)` [download] is equivalent to `!(!A and !B)` [download] Because of that, `(V != A) or (V != B)` [download] is equivalent to `!( (V == A) and (V == B) )` [download] If `A != B`, the "`and`" is obviously false (since `V` can't have two different values at the same time), and the whole statement is therefore true.	[reply] [d/l] [select]
Re^3: This is why Perl is so frustrating by jrsimmon (Hermit) on Jul 30, 2009 at 01:06 UTC
Yeah, I changed which side of the statement I was adding the A != B qualifier, didn't clean it up well. Thanks for clarifying it.	[reply]