Regexes for left, right, contains and exact

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November 22nd, 2012, 03:53 AM

Captain Planet

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Regexes for left, right, contains and exact

Hi, folks.

I'm looking for regular expressions which perform the following string functions:

left
right
contains
exact

I'm actually using VBScript, but the reason I can't use the built-in functions is because the user will be selecting the 'search type' on-the-fly. As such, I'll be generating thr RegExp pattern on-the-fly too.

An example string which I'm searching through could contain ANY character. An example might be:

HKLM\SYSTEM\CurrentControlSet\services\whatever

I'm not sure if the backslashes add complexity to the regexp? I was hoping there is a wildcard character to help me perform these?

At the moment, I've got the following....

'starts
'regexValid.Pattern = "^test"

'ends
'regexValid.Pattern = "test$"

'contains
'regexValid.Pattern = "test?"

'exact
regexValid.Pattern = "^test$"

Do these look ok? Of is there a fundamental regex aspect which I'm overlooking? Thanks..

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Last edited by Captain Planet : November 22nd, 2012 at 04:09 AM.

November 22nd, 2012, 08:27 AM

E-Oreo

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The start and end ones are correct. The contains one should not have a ? in it, that means "tes" optionally followed by a t. The exact match one will work too, but it's a lot more efficient to just use an equals comparison.

Remember that you'll have to escape all special regular expression characters that appear in the user input. Some languages have a utility function that does this, I'm not sure if vbscript does.

In almost all programming languages, using string comparison functions for these four types of matches is a lot more efficient that regexes.

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November 22nd, 2012, 08:59 AM

Jacques1

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Hi,

I don't even see why constructing different regexes is better than calling different functions. I mean, you'll have to go through each case, anyway.

November 22nd, 2012, 09:15 AM

Captain Planet

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Quote:

Originally Posted by E-Oreo

Remember that you'll have to escape all special regular expression characters that appear in the user input. Some languages have a utility function that does this, I'm not sure if vbscript does.

Thanks folks. Funny you mention the above, as I tested with:

C:\

and the backslash completely screwed it up. I replaced the "\" with a "\\" and it worked.

Hmmm. It'd be nice to treat a straing of text as a literal string (say, enclose it in brackets) or something similar.....so it doesnt parse things like "\" as a regexp symbol.

November 22nd, 2012, 09:21 AM

Captain Planet

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Using the following now for a test:

Code:

		CSSelectData = replace(CSSelectData,"\","\\")
		CSSelectData = replace(CSSelectData,"[","\[")
		CSSelectData = replace(CSSelectData,"^","\^")
		CSSelectData = replace(CSSelectData,"$","\$")
		CSSelectData = replace(CSSelectData,".","\.")
		CSSelectData = replace(CSSelectData,"|","\|")
		CSSelectData = replace(CSSelectData,"?","\?")
		CSSelectData = replace(CSSelectData,"*","\*")
		CSSelectData = replace(CSSelectData,"+","\+")
		CSSelectData = replace(CSSelectData,"(","\(")
		CSSelectData = replace(CSSelectData,")","\)")

Regexes for left, right, contains and exact

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