Regular Expression question

For an academic assignment, I need to make a regular expression to match a word with the following specifications:

• Word length >= 1 and <= 8
• Contai开发者_开发问答ns letters, digits, and underscore
• First digit can only be a letter
• Word is not A,X,S,T or PC,SW

I tried this regex but can't continue (My big problem is to make the word not equal to PC and SW)

([a-zA-Z&&[^AXST]])|([a-zA-Z][\w]{0,7})

But in the previous regex I didn't handle the that it is not PC and SW

Thanks,

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(?:^|\s)(?!PC)(?!SW)(?!A|S|T|X)(\w{1,8})

Explain this?

Highly suggest using an interactive regex tool for things like this. I use either http://regex.powertoy.org/ or http://gskinner.com/RegExr/ Then just play with them till you get it...

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Use negative-lookahead (?!pattern)

^(?!(?:A|X|S|T|PC|SW)$)(?=[A-Za-z])(\w{1,8}$)

regular-expressions.info

• Positive and Negative Lookahead

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rubular is a pretty good interactive regex tool as well.