RegexSafe() function for coldfusion

Posted by Paul Klinkenberg in CFML , Railo on November 14, 2010

It will probably already be out there somewhere, but I couldn't find it: a function which makes a string regular-expression-safe to use.

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Edit 15 nov. 2010: See Peter Boughton's comment underneath; the function I thought of could have been made a LOT simpler, so I am just posting his much appreciated code here:

<cffunction name="regExSafe" returntype="string" access="public" output="no">
	<cfargument name="text" type="string" required="yes" />
	<cfreturn rereplace(arguments.text, "(?=[\[\]\\^$.|?*+()])", "\", "all") />
</cffunction>

Thanks Peter!

Have tested this on ACF 8 and Railo 3.2.0.001.

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#1 by Peter Boughton - November 15, 2010 at 12:30 PM

Most of those backslashes are not required - character classes have different special characters - indeed several of the characters listed there are not special inside or outside of a character class.

And you don't need the wrapping parentheses - you've always got \0 for the entire match, so no need to create a \1 for it.

Also, a better tmp variable is chr(65535), since it's technically an invalid character and thus should never appear in input.

But there's a simpler way to workaround that Railo bug, you can use a lookahead instead (to match the position before the character and thus not require even \0), which then lets you use just a single \ and it works.

In summary, you can do this:
<cfreturn rereplace( arguments.text , "(?=[\[\]\\^$.|?*+()])" , "\" , "all" ) />

:)

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#2 by Paul Klinkenberg - November 15, 2010 at 1:51 PM

Hi Peter, thanks a lot! I learned two new things from your comment, great!
Please see the revised blog post: http://www.railodeveloper.com/post.cfm/regexsafe-function-for-coldfusion

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#3 by Ben Nadel - November 15, 2010 at 4:53 PM

@Peter,

Dang, that's pretty clever. I never though of replacing a zero-length match with an actual character (I'm not even sure I would have thought that was possible). Very cool!

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