Regex validation for numbers with comma separator

Question

Need a regular expression to validate number with comma separator. 1,5,10,55 is valid but 1,,,,10 is not valid.

Answer 1

This should do it:

^\d+(,\d+)*$

The regex is rather simple: \d+ is the first number, followed by optional commas and more numbers.

You may want to throw in \s* where you see fit, or remove all spaces before validation.

• To allow negative numbers replace \d+ with [+-]?\d+
• To allow fractions: replace \d+ with [+-]?\d+(?:\.\d+)?

Answer 2

Here are the components of the regex we're going to use:

• \d is the shorthand for the digit character class
• + is one-or-more repetition specifier
• * is zero-or-more repetition specifier
• (...) performs grouping
• ^ and $ are the beginning and end of the line anchors respectively

We can now compose the regex we need:

^\d+(,\d+)*$

That is:

from beginning...
|    ...to the end
|          |
^\d+(,\d+)*$              i.e. ^num(,num)*$
 \_/  \_/ 
 num  num

Note that the * means that having just one number is allowed. If you insist on at least two numbers, then use + instead. You can also replace \d+ with another pattern for the number to allow e.g. sign and/or fractional part.

References

• regular-expressions.info/Repetition, Character Classes, Grouping, Anchors

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Advanced topics: optimization

Optionally you can make the brackets non-capturing for performance:

^\d+(?:,\d+)*$

And if the flavor supports it, you can make all repetition possessive in this case:

^\d++(?:,\d++)*+$

References

• regular-expressions.info/Possessive