Re: regex syntax and idomatic Perl

precedence

http://perldoc.perl.org/perlop.html#Conditional-Operator

$x % 2 ? $x += 10 : $x += 2
[download]

Really means this:

 (($x % 2) ? ($x += 10) : $x) += 2
[download]

$capacity =($df_output =~ m[(\d+)%\s+/home$]) ? $1 : 'Match Error';
[download]

Comment on Re: regex syntax and idomatic Perl Select or Download Code

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Re^2: regex syntax and idomatic Perl by cbeckley (Curate) on Mar 21, 2017 at 13:33 UTC
Ah, ok. I see why `$capacity =($df_output =~ m[(\d+)%\s+/home$]) ? $1 : 'Match Error';` [download] is correct. Thank you for the link, otherwise my next question was going to why the previous version didn't produce an error. However, the fact that this operator can evaluate to an lvalue now prompts the next question, where else does this occur? Does any expression that evaluates to a object or variable work the same way? Thanks, cbeckley	[reply] [d/l]
Re^3: regex syntax and idomatic Perl by AnomalousMonk (Archbishop) on Mar 22, 2017 at 21:50 UTC
... the fact that this operator can evaluate to an lvalue now prompts the next question, where else does this occur? Does any expression that evaluates to a object or variable work the same way? Interesting question. All the more so since I have only a tenuous grasp of the syntactic/semantic issues involved. Obviously, something like `c:\@Work\Perl\monks>perl -wMstrict -le "my $t = 1; my $f = ''; ;; ($t \|\| $f) = 'foo'; print qq{t '$t' f '$f'}; " Can't modify logical or (\|\|) in scalar assignment ... Execution of -e aborted due to compilation errors.` [download] doesn't work: `($t \|\| $f)` can't be an lvalue. The only other situation I can think of in which this sort of hocus-pocus occurs is with Lvalue subroutines (see perlsub). I'd be interested to learn if there are any others. (Of course, now that I've asked the question, folks will probably respond with a million examples! :) BTW: the `?:` ternary operator in C/C++ has the same lvalue selection property. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^4: regex syntax and idomatic Perl by haukex (Archbishop) on Mar 22, 2017 at 22:04 UTC
substr is also an lvalue sub, but its return value can also be magic... `$ perl -lwMstrict my $x="abcdefghi"; for (substr $x,1,3) { print; s/c/C/; print; } print $x; my $y = \substr $x,5,3; $$y=~s/g/G/; print $x; __END__ bcd bCd abCdefghi abCdefGhi` [download]	[reply] [d/l]
Re^5: regex syntax and idomatic Perl by cbeckley (Curate) on Mar 22, 2017 at 23:33 UTC
Re^6: regex syntax and idomatic Perl by haukex (Archbishop) on Mar 23, 2017 at 11:20 UTC
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Re^6: regex syntax and idomatic Perl by AnomalousMonk (Archbishop) on Mar 23, 2017 at 01:43 UTC
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Re^4: regex syntax and idomatic Perl by cbeckley (Curate) on Mar 23, 2017 at 02:26 UTC
> (Of course, now that I've asked the question, folks will probably respond with a million examples! :) Bring it On! The first time I saw syntax like `obj.method(p1, pn).another_method(...).and_yet_another();` [download] I felt the earth move ... It wasn't Perl of course, but that's the kind thing ... well, it's why we keep doing this, isn't it?	[reply] [d/l]