Re: regex return true instead of false (precedence)

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

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery
FootballPerl is like chess, only without the dice}

Comment on Re: regex return true instead of false (precedence) Select or Download Code

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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
If you break a condition like that over multiple lines (and for a complicated or long condition I recommend it) put the operators at the front of the lines so they don't get "lost" at the back: `if ( $args =~ /\-rs(\s+)(\S+)/ \|\| $args =~ /\-p(\s+)(\S+)/ \|\| $args =~ /\-P(\s+)(\S+)/ )` [download] Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond	[reply] [d/l]
Re^5: regex return true instead of false (precedence) by Marshall (Canon) on Aug 26, 2019 at 21:29 UTC
Re^6: regex return true instead of false (precedence) by AnomalousMonk (Archbishop) on Aug 26, 2019 at 22:37 UTC
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Re^5: regex return true instead of false (precedence) by rsFalse (Chaplain) on Aug 27, 2019 at 16:40 UTC
Re^6: regex return true instead of false (precedence) by AnomalousMonk (Archbishop) on Aug 27, 2019 at 20:11 UTC
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