String replacement with regex...

amonotod has asked for the wisdom of the Perl Monks concerning the following question:

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Re: String replacement with regex... by bgreenlee (Friar) on Aug 06, 2004 at 15:05 UTC
ishnid beat me to it, so here's a nifty "simplification": `$bar =~ s/varchar\s*$(\d+)(??{$1<256})$/TEXT/i;` [download] update: I suppose it would be helpful to regex novices to give an explanation of the above: The `(??{ code })` construct (note: see the warning about this in perlre) evaluates the code inside the brackets, and treats the results as if it were part of the regex. If the number captured by `(\d+)` is less than 256, it returns a 1. The parser then tries to match on that 1 and fails, since the `\d+` already sucked up all the digits. If the number is 256 or greater, the expression returns a blank string (not 0), so the regex matches. See perlre and perlretut for all the gory details. Brad	[reply] [d/l] [select]
Re^2: String replacement with regex... by Gilimanjaro (Hermit) on Aug 06, 2004 at 15:24 UTC
Or if using (??) is not desired: `$bar =~ s/varchar\s$\d\|\d\d\|2[0-4]\d\|25[0-5])$/TEXT/i;` [download] Or split up for readbility: `$byte = qr/\d\|\dd\|2[0-4]\d\|25[0-5]/; $bar =~ s/varchar\s$$byte)$/TEXT/i;` [download]	[reply] [d/l] [select]
Re^3: String replacement with regex... by Eimi Metamorphoumai (Deacon) on Aug 06, 2004 at 16:05 UTC
If I read it correctly, that's backwards, matching numbers less than or equal to 255 instead of numbers strictly greater than 255. (The post you're replying to was doing very clever things with truth and falsehood.)	[reply]
Re^4: String replacement with regex... by Gilimanjaro (Hermit) on Aug 09, 2004 at 09:40 UTC
Re^2: String replacement with regex... by amonotod (Acolyte) on Aug 06, 2004 at 16:15 UTC
Okay, so I thought it was working, and it is... But too expansively. Using `$buffer =~ s/varchar\s*$(\d+)(??{$1<256})$/TEXT/i;` as my replacement function, I'm getting conversions on this column, for some reason... Discrepancy_Filename VARCHAR (40) NULL becomes Discrepancy_Filename TEXT NULL Ideas? Thanks, amonotod	[reply] [d/l]
Re^3: String replacement with regex... by bgreenlee (Friar) on Aug 06, 2004 at 19:58 UTC
Odd...it works fine for me. Would it be possible for you to post a snippet of code that shows it not working? Brad	[reply]
Re: String replacement with regex... by bart (Canon) on Aug 07, 2004 at 09:15 UTC
~~I think your update is comparing towards the wrong direction.~~ No, apparently it isn't. This assertion stuff is tricky! Anyway, here's an alternative: it replaces the text by itself if the number is small enough (effectlively doing nothing as a result), by 'TEXT' if it needs replacing. `$bar =~ s/(varchar\s*$(\d+)$)/$2 >= 256 ? 'TEXT' : $1/gei;` [download]	[reply] [d/l]
Re: String replacement with regex... by ishnid (Monk) on Aug 06, 2004 at 15:04 UTC
In that code, $1 won't be set, as you haven't included any capturing groups in your regexp (the only parens you have are escaped to match paren characters): `$buffer =~ s/varchar $\d+$/TEXT/ig if (/varchar $(\d+)$/i and $1 > + 255);` [download] Update: Typo corrected as per Eimi's post below. Thanks for the correction.	[reply] [d/l]
Re^2: String replacement with regex... by Eimi Metamorphoumai (Deacon) on Aug 06, 2004 at 15:32 UTC
You've got a small typo--should be "`(\d`" instead of "`$d`". One other thing with the solutions--they replace all varchars on the line with texts if any of them have over 255 characters. That may not be a problem depending on how things are broken up, but it's something to notice. `CREATE TABLE varchar (15) LastName, varchar (300) Notes` [download] (Apologies if my SQL is off, it's been a long time.) So here's just one more way to do it: `$buffer =~ s/varchar\s\( (?: \d{4,} \| 2 (?: 5 [6-9] \d \| [6-9] \d+ ) \| [3-9]\d{2,} )$/TEXT/gix;` [download]	[reply] [d/l] [select]