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I need to check that a file contains some amounts that match a specific format:

  • between 1 and 15 characters (numbers or ",")
  • may contains at most one "," separator for decimals
  • must at least have one number before the separator
  • this amount is supposed to be in the middle of a string, bounded by alphabetical characters (but we have to exclude the malformed files).

I currently have this: 

\d{1,15}(,\d{1,14})?

But it does not match with the requirement as I might catch up to 30 characters here.
Unfortunately, for some reasons that are too long to explain here, I cannot simply pick a substring or use any other java call. The match has to be in a single, java-compatible, regular expression.

gizmo
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    It would be useful to know if you know the limits of what's being checked. It is, you have the exact string to match against a ^...$ expression, or you try to match that expression in the middle of other things... – helios Sep 03 '10 at 10:28
  • I'm matching in the middle of other things, I'll update the question. – gizmo Sep 03 '10 at 10:57
  • In that case replace `^` and `$` in my answer with `\b` – Amarghosh Sep 03 '10 at 11:11

1 Answers1

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^(?=.{1,15}$)\d+(,\d+)?$
  • ^ start of the string
  • (?=.{1,15}$) positive lookahead to make sure that the total length of string is between 1 and 15
  • \d+ one or more digit(s)
  • (,\d+)? optionally followed by a comma and more digits
  • $ end of the string (not really required as we already checked for it in the lookahead).

You might have to escape backslashes for Java: ^(?=.{1,15}$)\\d+(,\\d+)?$

update: If you're looking for this in the middle of another string, use word boundaries \b instead of string boundaries (^ and $).

\b(?=[\d,]{1,15}\b)\d+(,\d+)?\b

For java:

"\\b(?=[\\d,]{1,15}\\b)\\d+(,\\d+)?\\b"

More readable version:

"\\b(?=[0-9,]{1,15}\\b)[0-9]+(,[0-9]+)?\\b"
Community
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Amarghosh
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  • Thanks for your reply. I updated the requirement with a missing part but was able to adapt your proposal so that it fit in the enclosing regexp. I end up with (?=[,0-9]{1,15}[a-zA-Z])\d+(,\d+)? and it works with the checks that are done previously. – gizmo Sep 03 '10 at 11:15
  • @gizmo `\b` won't work if the number is immediately followed by a letter. But looks like you've already figured it out. – Amarghosh Sep 03 '10 at 11:17