Help with negative lookahead in regular expression.

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March 30th, 2011, 05:05 PM

dissectcode

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Other Language - Help with negative lookahead in regular expression.

I am creating a tool which has a command line option "-d" to specify which usb device to use. I need to make sure there are no characters and I was tyring to use a negative-lookahead. Why doesn't this work in my .l file? :

Code:

-device { 
    BEGIN DEVICE_NUM; 
}
<DEVICE_NUM>[ ]+   /* ignore whitespace */
<DEVICE_NUM>^(?!.[a-zA-Z]*)[0-9]+$  {  // fails here
.............

I get this error:
"./mytool.l", line 262: unrecognized rule

please help

March 30th, 2011, 06:19 PM

requinix

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You don't have to check for letters if you require only digits.

Code:

<DEVICE_NUM>^[0-9 ]+$

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March 31st, 2011, 08:28 AM

dissectcode

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Quote:

Originally Posted by requinix

You don't have to check for letters if you require only digits.

Code:

<DEVICE_NUM>^[0-9 ]+$

I did that but if someone enters an invalid parameter like FTQ7VVR

it will extract the 7 - that's why I need to make sure only a digit 0-9 is entered. please help

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