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Regular Expressions

Posted on 2008-10-18
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Last Modified: 2013-11-23
hello experts,

i've been given the following regular expression "\\.\\d+|\\d+(?:\\.\\d+)?|[+-/*()%^]|\\w{3,4}|[a-zA-Z]" and im having a little trouble decoding it.

from my understanding of RE's (which isnt very much), this expression is split up into four types/categories. "[+-/*()%^]" being the normal chars, "\\w{3,4}" i would think are words of 3 or 4 letters, "[a-zA-Z]" being a letter of the alphabet, however i have absolutely no idea what the first two categories ("\\.\\d+|\\d+(?:\\.\\d+)?") represent. im guessing it has to do with numerical float values, but other then that no clue.

anyone have any idea?

cheers
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Question by:gem56
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5 Comments
 
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Expert Comment

by:miqrogroove
ID: 22751216
\\.\\d+
This is a literal period, followed by one or more digits.

\\d+(?:\\.\\d+)?
This one I'm a bit confused about myself.  If I can give you a solid intrepretation I will follow up.
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miqrogroove earned 125 total points
ID: 22751224
\\d+(?:\\.\\d+)?
One or more digits followed optionally by: a literal period and one or more digits.

The syntax (?:) creates a non-backreferenced grouping, which is done only for speed optimization.

Enjoy!
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Author Comment

by:gem56
ID: 22751228
thanks mate.

by the looks of it "\\d+(?:\\.\\d+)?" will probably translate to <digit>.<more digits> so looks like its just a formatting thing so it matches both "0.45" and ".45". any chance you could confirm?

cheers
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Expert Comment

by:miqrogroove
ID: 22751235
See my second message ;)

"\\d+(?:\\.\\d+)?" will match "0.45" and not ".45"
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Author Comment

by:gem56
ID: 22751302
yep, beat me to the post :P

thanks champ

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