Re^5: why my reg ex matches greedy?

I don't see the relation between your link and that bit of the regex. However, that said, your skepticism of its utility seems justified. I tried to find a use for it, but I haven't been able to make \d{4,}? act any differently than \d{4}. It's either a useless construct, or a failure of my imagination in coming up with an appropriate test case.

Putting aside what YAPE::Regex::Explain says about it, when I looked at it originally, I thought "Yack! Perl is gonna bitch about that weird '?' character". I could think of a couple other interpretations, so I put together a bit of code to check 'em out:

my @tests = (               
    'First case',           
    '123456789second & third case',
);                          
                            
for my $t (@tests) {        
    print "\nchecking '$t'\n";                                        
+          
    if ($t=~/(\d{4,}?)(.*)/)   { print "A: $1, $2\n"; }
    if ($t=~/(\d{4,}?)(.*?)$/) { print "B: $1, $2\n"; }
}
[download]

The other interpretations I could think of were:

An optional set of 4 or more digits, kind of like (?:\d{4,})?. If true, the first case would give us:
```
A: , First case'
[download]
```

Exactly 4 digits, like \d{4}, giving us:

checking '123456789second & third case'
A: 1234, 56789second & third case
B: 1234, 56789second & third case
[download]

4 or more digits, with as few as possible, yielding:

checking '123456789second & third case'
A: 1234, 56789second & third case
B: 123456789, second & third case
[download]

On reading the ...explain() output, I thought that I could perhaps make the third case come about. But what I actually got was:

$ perl xxxyyyzzz.pl

checking 'First case'

checking '123456789second & third case'
A: 1234, 56789second & third case
B: 1234, 56789second & third case
[download]

So I'm thinking that my initial surprise was justified, even though it's syntactically correct.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Comment on Re^5: why my reg ex matches greedy? Select or Download Code

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Re^6: why my reg ex matches greedy? by GrandFather (Saint) on Jun 26, 2012 at 21:01 UTC
It's different if there is some following match condition: `use strict; use warnings; for my $reg ('(x\d{3,}?)', '(x\d{3,}?x)', '(x\d{3,})', '(x\d{3})') { for my $str ('xx', 'x12x', 'x123456x', 'x12x x123x') { print "Matched using $reg: $1\n" if $str =~ $reg; } }` [download] Prints: `Matched using (x\d{3,}?): x123 Matched using (x\d{3,}?): x123 Matched using (x\d{3,}?x): x123456x Matched using (x\d{3,}?x): x123x Matched using (x\d{3,}): x123456 Matched using (x\d{3,}): x123 Matched using (x\d{3}): x123 Matched using (x\d{3}): x123` [download] True laziness is hard work	[reply] [d/l] [select]
Re^7: why my reg ex matches greedy? by roboticus (Chancellor) on Jun 26, 2012 at 22:27 UTC
GrandFather: Thanks. I updated your code to make it a little more visually obvious to me, then added a couple cases. Now that I see what the difference is, I doubt that I'd ever use it. Not because it isn't useful, but rather because if I ever need it, I'm sure I'll have long forgotten it. But it's certainly educational. For grins, here's what I came up with: $ cat splok.pl use strict; use warnings; my @regs = ('(x\d{3,}?)', '(x\d{3,}?x)', '(x\d{3,})', '(x\d{3})', '(x\d{3,}x)', '(x\d{3,}?x?)'); my @strs = ('xx', 'x12x', 'x123456x', 'x12x x123x', 'x123456y'); printf "%-12.12s ", $_ for " ", @regs; print "\n"; for my $str (@strs) { printf "%-12.12s ", $str; for my $reg (@regs) { printf "%-12.12s ", ($str=~$reg) ? $1: '-nope-'; } print "\n"; } $ perl splok.pl (x\d{3,}?) (x\d{3,}?x) (x\d{3,}) (x\d{3}) (x\d{ +3,}x) (x\d{3,}?x?) xx -nope- -nope- -nope- -nope- -nope +- -nope- x12x -nope- -nope- -nope- -nope- -nope +- -nope- x123456x x123 x123456x x123456 x123 x1234 +56x x123 x12x x123x x123 x123x x123 x123 x123x + x123x x123456y x123 -nope- x123456 x123 -nope +- x123 [download] (As you can tell, I like things laid out in grids. I organize lots of stuff with database tables and spreadsheets...) ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply] [d/l]