SRE - adding chars to pattern produces invalid results

[kylomas]

In the following code the first SRE produces what I am looking for but the second does not. It seems like it should produce the same result.

#include <array.au3>

; This works

local $str = '<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>'
$aTemp = stringregexp($str,'>(.*?)<',3)
_arraydisplay($aTemp,'Without /a')

; This returns too much

local $str = '<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>'
$aTemp = stringregexp($str,'>(.*?)</a',3)   ; added /a to pattern
_arraydisplay($aTemp,'With /a')

Can someone explain why, please?

kylomas

[AZJIO]

1.

<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>

2.

<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>

[kylomas]

AZJIO,

Yes, I see that, but why?

kylomas

[AZJIO]

Because you're so requested

All according to the requesting

$aTemp = StringRegExp($str, '>([\d\s]+?)</a', 3)
$aTemp = StringRegExp($str, '>([^<>]+?)</a', 3)

Edited April 6, 2013 by AZJIO

[kylomas]

AZJIO,

Yes, my apologies for such a vague question...these SRE's are frustrating the crap out of me.

The question that I hould have asked is, "why does the second pattern not match on the bold string below?

<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>

kylomas

[BrewManNH]

Because it matches from the first GT symbol, to the </a. It's not going to use the last >, it's going to start matching from the first.

[kylomas]

Because it matches from the first GT symbol, to the </a. It's not going to use the last >, it's going to start matching from the first.

@BrewmanNH - Then why doesn't it do the same thing with the first pattern?

edit: AZJIO - thanks for the SRE you posted, but I will never undertand this if I don't undertand why my pattern did NOT work...

Edited April 6, 2013 by kylomas

[AZJIO]

Because pattern another. He found a pair.

[kylomas]

You guys ever have this dream where everyone get's it or is included, except you?

I'm having that dream now, maybe when I go to sleep the whole shit will make sense!

kylomas

[AZJIO]

[ds] - allows only numbers and spaces

There are no numbers "<a src". So the following search.

[kylomas]

[ds] - allows only numbers and spaces

There are no numbers "<a src". So the following search.

I get why you patterns work, I do NOT get why this '>(.*?)</a' does'nt.

kylomas

[AZJIO]

Finds the first character >

.*? - search of all that will meet on the way

stop during a meeting with this </a

[kylomas]

OK, but does'nt the '?' make it non-greedy (matching smallest possible group)?

[AZJIO]

Yes, without the symbol "?" will be searched to the last character </a

But he is in one copy

[kylomas]

For me, both these patterns produce the same results:

'>(.*?)</a'

'>(.*)</a'

The above is incorrect, but the question still remains...

I thought the "?" would make the pattern non-greedy so it would match the smallest match possible, e.g.

<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>

kylomas

Edited April 6, 2013 by kylomas

[kylomas]

AZJIO,

Thank you for trying to help me. I am missing something fundamental to SRE and wasting your time. I'll come back to this later, after I've read more PCRE doc.

Again, thanks,

kylomas

[AZJIO]

kylomas,

[PhoenixXL]

QuickTip

• Use Flag 4 for debugging when your regex doesn't fit your expectations

#include <array.au3>

Local $str = '<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>'
$aTemp = StringRegExp($str, '>(.*?)</a', 4) ; added /a to pattern

;Lets check what happened
For $i = 0 To UBound($aTemp) - 1
$l = $aTemp[$i]
_ArrayDisplay($l, 'With /a')
Next

;Hope you understand what happened

Regards

[PhoenixXL]

Workaround

#include <array.au3>

Local $str = '<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>'
$aTemp = StringRegExp($str, '.*>(.*?)</a', 3) ; added /a to pattern

;The Greedy part will capture everything, then upon back-tracing the last match would be found
_ArrayDisplay($aTemp)

Regards

[kylomas]

;The Greedy part will capture everything, then upon back-tracing the last match would be found

Exactly what I don't understand...Why does'nt '>(.*?)</a' find the smallest match?

'<img width="20" height="22"> <a src="/icons/text.gif" alt="[TXT]" 2732618_readme.htm href="2790817%202732618_readme.htm"> 2790817 </a>'