I have a regex that will validate to make sure I have a number. but it passed if the string I'm checking is "" as well. how can I make a "" fail?
^(\\d|-)?(\\d|,)*\\.?\\d*$
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2Just check for "" separately. Boo regex, boo!Alex– Alex2010-10-12 20:52:04 +00:00Commented Oct 12, 2010 at 20:52
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I want this to accept number: 1,120.03 or 100,100,200.30 or 10002 or .05Justin808– Justin8082010-10-12 20:55:11 +00:00Commented Oct 12, 2010 at 20:55
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5 Answers
You could require at least one digit:
^-?\d[\d,]*(?:\.\d+)?$
^^
required
To also allow matching .05:
^-?\d[\d,]*(?:\.\d+)?$|^-?\.\d+$
Note that your expression also allows multiple commas one after another which may not be desirable.
Comments
What language are you using? There's undoubtedly a better way for you to detect "is this a number?" than rolling your own regex from scratch. If you're using Perl, then look at the Regexp::Common module that provides dozens of time-tested regexes for your use.
Comments
try
^-?([0-9]+)(,[0-9]+)?$
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How about...
^-?\d+(,\d{3})*(\.\d+)?$|^-?\.\d+$
Tested it on Rubular, which is awesome (thanks, Mark!) It'll accept some sloppy comma management, like "1234,567", but will reject obvious crap like "123,,,,456".
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This is the proper regex for grouped decimals:
^-?(?:\\.\\d+|\\d{1,3}(?:,\\d{3})*(\\.\\d*)?)$
- It accepts an initial sign.
- After that it creates a tree with two paths, either period or 1-3 digits.
- If it doesn't have either of those, it fails.
- If it sees a period, then it will take any number of digits, but at least 1.
- If it sees a digit cluster, it will take any number of groups consisting of comma + 3 digits.
- Then, you can have a decimal point, if you want and follow it up with as many digits as you would like.
The following fix handles ungrouped numbers as well:
^-?(?:\\.\\d+|\\d{1,3}(?:\\d*|(?:,\\d{3})+)(\\.\\d*)?)$
But it does not allow somebody to include more than 3 in a group. Thus after 1-3 digits, there must be another digit or a comma or a period or the end.
- If it's a digit, then nothing but a digit or a period can follow.
- Given a comma, nothing but 3 digits can follow. We intensified this to 1 or more, since
\\d*handles the case of an immediate period.
