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deciphering a regular expression

Posted on 2012-03-30
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Sorry for the simple question, but I'm not familiar with regular expressions.

Does the following regex [0-9][A-Za-z][0-9][A-Za-z] mean the following:

The first character has to be a number 0-9 then the next character has to be a-z (uppercase or lowercase) then the next character has to be a number 0-9 and then finally the last character must be a-z (uppercase or lowercase)?

Is that correct?
Thank you.
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Question by:-Dman100-
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käµfm³d   👽 earned 2000 total points
ID: 37787894
Depending on the language/text editor it might. The only reason I say that is because some languages treat the entire input string (being searched) as the entire match whereas others will look anywhere within the string (i.e. any substring which matches the pattern will be considered a match). To be safe, I'd suggest adding boundary conditions to prevent substring matches--unless you don't care about substring vs entire string matches.

e.g.

^[0-9][A-Za-z][0-9][A-Za-z]$

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Here, the ^ means beginning of the string and $ means end of the string. Adding these constructs would prevent substring matches.

Other than that, your interpretation is correct.
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by:käµfm³d 👽
ID: 37787900
P.S.

I recommend this site for an extensive, yet easy-to-understand breakdown of regex:  www.regular-expressions.info .
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