regex return true instead of false

ovedpo15 has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: regex return true instead of false by haukex (Archbishop) on Aug 26, 2019 at 11:43 UTC
The difference between your first and second examples is that you've swapped out the `\|\|` for `&&` operators. If you hadn't done that, it works - `unless (condition) {code}` is equivalent to `if (condition) {} else {code}` and `if ( not (condition) ) {code}`, but there is no change to `condition` needed. In the third example, due to operator precedence, `!$var =~ /regex/` is equivalent to `(!$var) =~ /regex/`. Although you could use parentheses, the better way to write that is `$var !~ /regex/`. Also, you need to swap the `unless` for an `if`, since the question you're asking is "if `$args` doesn't contain this thing, and `$args` doesn't contain this other thing", not the opposite of this condition. Update: Tested some more, and added the last sentence.	[reply] [d/l] [select]
Re: regex return true instead of false (precedence) by LanX (Saint) on Aug 26, 2019 at 11:46 UTC
your `!` has higher precedence than `=~` , please note the (parens) due to -p flag in B::Deparse `d:\exp>perl -MO=Deparse,-p -e"if (! $args =~ /\-rs(\s+)(\S+)/ && ! $ar +gs =~ /\-p(\s+)(\S+)/ && ! $args =~ /\-P(\s+)(\S+)/){1}" if (((((!$args) =~ /\-rs(\s+)(\S+)/) and ((!$args) =~ /\-p(\s+)(\S+)/) +) and ((!$args) =~ /\-P(\s+)(\S+)/))) { '???'; } -e syntax OK` [download] I'd say either use `not` instead of `!` or just `!~` instaed of `=~` and I'd also recommend using `and` instead of `&&` EDIT you might be interested in reading perlop#Operator-Precedence-and-Associativity perlop#Logical-Not Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l] [select]
Re^2: regex return true instead of false (precedence) by Ratazong (Monsignor) on Aug 26, 2019 at 13:52 UTC
The easiest way to get around precedence-issues is to define precedence yourself by using (a lot of) brackets. So `unless (! $args =~ /\-rs(\s+)(\S+)/ && ! $args =~ /\-p(\s+)(\S+)/ && ! + $args =~ /\-P(\s+)(\S+)/) {` [download] will become `unless ((!($args =~ /\-rs(\s+)(\S+)/)) && (!($args =~ /\-p(\s+)(\S+)/) +) && (!($args =~ /\-P(\s+)(\S+)/))) {` [download] I agree it looks a bit confusing, but modern editors help you by showing the matching bracket. And you don't have to think about rules (which might be counter-intuitive (like ! vs =~) or different in other programming languages). HTH, Rata	[reply] [d/l] [select]
Re^3: regex return true instead of false (precedence) by LanX (Saint) on Aug 26, 2019 at 16:59 UTC
I agree that it's better to over use brackets than forgetting them. On the other hand there's a good reason why Perl has that many operators. And, not, or won't bite you in Boolean expressions because they have the lowest precedence. (But I use brackets when combining them, I need a complicated mnemonic to remember that and has higher precedence than or) And !~ is really underused. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply]
Re^3: regex return true instead of false (precedence) by Marshall (Canon) on Aug 26, 2019 at 18:00 UTC
I prefer to use indenting to make all the parens more clear. Also, this "unless not" syntax can be confusing. I think I got this right, but it is easy to make a mistake. Consider: # X is the "default action" # do X with an exception that when A,B and C are all false # then don't do X unless (!A and !B and !C) {X} # if anybody is true then they all can't be false # so we do X unless anybody is true (meaning they # can't all be false) unless (A or B or C) {X} ------- unless ( (!($args =~ /\-rs(\s+)(\S+)/)) && (!($args =~ /\-p(\s+)(\S+)/)) && (!($args =~ /\-P(\s+)(\S+)/)) ) {..... # I figure this is easier to understand: unless ( $args =~ /\-rs(\s+)(\S+)/ or $args =~ /\-p(\s+)(\S+)/ or $args =~ /\-P(\s+)(\S+)/ ) {.... [download]	[reply] [d/l]
Re^4: regex return true instead of false (precedence) by GrandFather (Saint) on Aug 26, 2019 at 21:10 UTC
Re^5: regex return true instead of false (precedence) by Marshall (Canon) on Aug 26, 2019 at 21:29 UTC
Some notes below your chosen depth have not been shown here
Re^5: regex return true instead of false (precedence) by rsFalse (Chaplain) on Aug 27, 2019 at 16:40 UTC
Some notes below your chosen depth have not been shown here
Re: regex return true instead of false by Corion (Patriarch) on Aug 26, 2019 at 11:43 UTC
Please edit your post and show us the values of `$args` that match and the values that don't match. Also, it looks as if you are trying to parse command line parameters. Have you looked at Getopt::Long?	[reply] [d/l]
Re: regex return true instead of false by AnomalousMonk (Archbishop) on Aug 26, 2019 at 22:59 UTC
Please note that if `$args =~ /\-rs(\s+)(\S+)/ \|\| $args =~ /\-p(\s+)(\S+)/ \|\| $args =~ /\-P(\s+)(\S+)/` actually works for your purposes, it can be simplified to `$args =~ m{ - (?: rs \| p \| P) (\s+) (\S+) }xms` or its negation `$args !~ m{ - (?: rs \| p \| P) (\s+) (\S+) }xms` and you need not torture your brain with De Morgan's laws. And `(?: rs \| p \| P)` could be further simplified to `(?: rs \| [pP])` although I find the first form a bit neater somehow. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re: regex return true instead of false by jwkrahn (Abbot) on Aug 26, 2019 at 22:40 UTC
It looks like you may need: `if ( $args !~ /\-rs(\s+)(\S+)/ && $args !~ /\-p(\s+)(\S+)/ && $args !~ + /\-P(\s+)(\S+)/ ) { $args .= " --rs $str"; }` [download]	[reply] [d/l]


go ahead... be a heretic
	PerlMonks

regex return true instead of false

EDIT