Regex - how to make my regex not pass when the string is blank

Question

Hi, 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*$

Answer 1

try

^-?([0-9]+)(,[0-9]+)?$

Answer 2

You could require at least one digit:

^-?\d[\d,]*(?:\.\d+)?$
   ^^
required

Rubular

To also allow matching .05:

^-?\d[\d,]*(?:\.\d+)?$|^-?\.\d+$

Rubular

Note that your expression also allows multiple commas one after another which may not be desirable.

Answer 3

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".

Answer 4

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.

Answer 5

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.