Kevin Zembower wrote:
>
> I'm still having trouble with the regex expression. I've pasted in
> the files and program at the end, for reference.
>
> In your message, you said:
> my %hash = ( abstract => '', author => '', endtitle => '' );
> $hash{ lc $2 } = $3
> while $query =~
> /QF(\d+)=[^&]*\b(abstract|author|endtitle)\b(?=.*?&QI\1=([^&]*))/ig;
>
> My interpretation of the match statement is:
> Match the letters 'QF' then one or more digits. Capture the digits in \1
> Match anything, or nothing, as long as it's not '&', then look for the
> start of a word, followed by one of the words 'abstract', 'author' or
> 'endtitle' followed by the end of a word. Capture that in the \2 or $2
> variable.
Correct so far.
> Here's where I have a problem: I don't understand the '(' (start the
> third group?) followed by the '?'.
The (?=pattern) is a zero-width positive look-ahead assertion. It does
not capture to a numeric variable and it does not affect the position of
the next match. The reason I used it is suppose that you had a string
like:
&QF0=something&QF1=something&QI0=something&QI1=something&
With the zero-width positive look-ahead assertion you would match both 0
and 1 but without it you would only match 0.
> I'll skip up to the 'QI' for now
> Match the letters "QI" followed by the digits captured in \1, then an
> equals sign, then anything or nothing, as long as it's not '&', and
> capture that in the \4 or $4 variable.
No, in the $3 variable.
> I tried to rewrite this statement as:
> my %hash = (abstract =>'', author =>'', endtitle =>'');
> $hash{lc $2}=$3 while $query =~ \
> /QF(\d+)=[^&]*\b(abstract|author|endtitle)\b.*?&QI\1=([^&]*)/ig;
>
> Which I think means:
> Match the letters 'QF' then one or more digits. Capture the digits in \1
> Match anything, or nothing, as long as it's not '&', then look for the
> start of a word, followed by one of the words 'abstract', 'author' or
> 'endtitle' followed by the end of a word. Capture that in the \2 or $2
> variable.
> Match anything, but as little as possible (".*?"), up to '&QI' then the
> same digits as before, then
> then anything or nothing, as long as it's not '&', and capture that in
> the \3 or $3 variable.
>
> However, this still isn't matching anything, as the output of the program
> with the data file 'v' below shows.
That is because you have a '\' character between '=~' and the match
operator. Remove that and it should work.
John
--
use Perl;
program
fulfillment
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