The \1 is a backreference and will match the same thing that the first parenthesis matched. It isn't all that useful in this example since it could be rewritten as /(is) is/ but something like /(\d)\1/ would match on the same number twice in a row (because the \1 matches the same number that was found with the (\d)), thinking up more useful examples will be an exercise left up to the reader. | [reply]
[d/l]
[select] |
(simplified to some extent)
the two /'s specify the matching operator (also seen as m//). this match operator allows you to search for certain regular expressions in a string. in this case, you are searching for 'is' which gets captured by the parentheses. this means that 'is' gets stored in the \1 variable. so you are searching for 'is' then a single space, then another 'is'. so where are you searching? well, the matching operator defaults to the $_ special variable (doesn't everything?). so you are looking in $_ for 'is is'. you can also specify a string to search in using the binding operator =~. so this expression could also be written as:
$_ =~ m/is is/ # or
$_ =~ m/(is) \1/
the parentheses around the statement simply means that this is a test (for an if or a while or something).
you should really check out the perlre manpage or 'Learning Perl' by O'Reilly or something for a much more detailed explanation of regular expressions.
jeff | [reply]
[d/l]
[select] |
Thank you very much for your response. Did you guys by any chance know if there is any good regular expression website.Thanks again. | [reply] |
The perlre man page is quite useful. Mastering Regular Expressions is a great book (IMO), and is now available to read online (link removed by KM).
Cheers,
KM
| [reply] |
Ok, the following is a message that I sent to the author of the book, and his reply:
|> I stumbled across your book online at
|> http://public.yahoo.com/~jfriedl/mre/
Wow, could I ask how you stumbled across that? It's not supposed to
be public.
|> it appeared that you may not have intended to have the entire book
|> freely available online.
|>
|> Am I free to post links to the full online version of your book?
Please don't, and thanks for asking / bringing it to my attention.
If you've grabbed a copy for yourself, please don't share it publically.
It's probably too late (I see from the logs that a number of copies
have gone out, so I'm probably sunk anyway )-:
Again, thanks for bringing it to my attention,
Jeffrey
| [reply] |
KM,
[snip text accusing KM of posting pirated material]
Update: Very sorry, I just looked at the URL and noticed that it contains the authors name. So apparently this is a perfectly legit link. Its great to see authors posting their work online, and I voted your post ++.
| [reply] |