Perl, Help with regular expression

Help with regular expression

Author	Message
Larry Rosl #1 / 6	Help with regular expression [Posted to comp.lang.perl.misc and copy mailed.] Quote: > I'm trying to parse table rows in a pathological html document. The document > doesn't have any closing tags for <table>, <tr>, <th>, or <td>. This is what I I'll bet it has </table> or it wouldn't display at all. Quote: > tried that did not work: > while ( $html =~ m#(<tr>.?)<tr>)#gs ) { > # do stuff > } You couldn't have tried exactly that, because the parentheses don't match. However... Quote: > It picks up every other row because I have run past the beginning of the row > tag with the second "<tr>". Is there a way to tell perl to 'put back' the four > characters before continuing the match? How should I be doing this? (?=...) means look but don't touch. So try this: while ( $html =~ m#(<tr>.?)(?=<tr>)#gis ) { Now the parentheses match :-). I've added the /i modifier because you want to ignore case for HTML tags. How will you deal with the last row of the table (i.e., no following <tr>)? You might want to change that look-ahead to (?=(<tr>\|</table>)). As I said, I'll bet there is an </table> tag. HTH, -- Larry Rosler Hewlett-Packard Laboratories http://www.--*.com/
Wed, 24 Jan 2001 03:00:00 GMT

Awrobins #2 / 6	Help with regular expression I'm trying to parse table rows in a pathological html document. The document doesn't have any closing tags for <table>, <tr>, <th>, or <td>. This is what I tried that did not work: while ( $html =~ m#(<tr>.*?)<tr>)#gs ) { # do stuff } It picks up every other row because I have run past the beginning of the row tag with the second "<tr>". Is there a way to tell perl to 'put back' the four characters before continuing the match? How should I be doing this? Thanks! Andrew Robinson Andrew Robinson --- Disclaimer: The opinions expressed are mine alone and do not represent the views of America Online
Thu, 25 Jan 2001 03:00:00 GMT

Michael J Geb #3 / 6	Help with regular expression Quote: }I'm trying to parse table rows in a pathological html document. The document }doesn't have any closing tags for <table>, <tr>, <th>, or <td>. This is what I }tried that did not work: } while ( $html =~ m#(<tr>.*?)<tr>)#gs ) { } # do stuff } } }It picks up every other row because I have run past the beginning of the row }tag with the second "<tr>". Is there a way to tell perl to 'put back' the four }characters before continuing the match? How should I be doing this? Look up "lookahead" in the man pages (or for true insights, Friedl's Mastering Regular Expressions.) Then use it. --
Thu, 25 Jan 2001 03:00:00 GMT

Craig Ber #4 / 6	Help with regular expression : How will you deal with the last row of the table (i.e., no following : <tr>)? You might want to change that look-ahead to (?=(<tr>\|</table>)). First, you'll want to make thos non-capturing parens or you'll mess up what gets returned on each /g iteration. Second, there's a minor optimization possible which only matters if you're doing this a lot -- putting the common < and > outside the alternation. Third, though this becomes irrelvant, the parent grouping around the alternation is unnecessary. Combining the these: (?=<(?:tr\|/table)>) --------------------------------------------------------------------- --*-- Home Page: http://www.cinenet.net/users/cberry/home.html \| Member of The HTML Writers Guild: http://www.hwg.org/ "Every man and every woman is a star."
Thu, 25 Jan 2001 03:00:00 GMT

Awrobins #5 / 6	Help with regular expression Quote: >(?=...) means look but don't touch. So try this: > while ( $html =~ m#(<tr>.*?)(?=<tr>)#gis ) { Thanks to everyone who suggested lookahead. That was what I needed and did not know. Quote: >As I said, I'll bet there is an </table> tag. There was not. The body of the document consisted entirely of tables. One table ended with the beginning tag of the next table. The last one was terminated by the </html> tag. Surprised me too, but Netscape had no trouble rendering it. Thanks everyone for the help. Andrew Robinson --- Disclaimer: The opinions expressed are mine alone and do not represent the views of America Online
Thu, 25 Jan 2001 03:00:00 GMT

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