Regex expression to match equal or greater than 0,5 or 0.5, by increments of .5

Question

I am trying enhance the given answer on another post:

^[1-9]\d*(?:\.[05])?$

Breakup:

^        # Start of input
[1-9]    # match digit 1 to 9
\d*      # match 0 or more of any digits
(?:      # start of non-capturing group
\.       # match a decimal
[05]     # followed by digit 0 or 5
)?       # end non-capturing group. (? makes this group optional)
$        # End of input

Only this time the regex needs to accept 0,5 or 0.5 and increments of 0,5 or 0.5

The number zero is the only one that can't be matched.

Already tried:

(?!0).{1}|^[1-9]\d*(?:(,|\.)[05])?$

and

[^0]|^[1-9]\d*(?:(,|\.)[05])?$

Can you help please?

Must accept 0,5 or 0.5 Number 0 is not allowed. Commas or point should be allowed as decimal separator. Increments by 0.5 (or 0,5) are matched. — Francisco Ramilo, Nov 12 '15 at 17:48

Wiktor Stribiżew · Accepted Answer · 2015-11-12T18:01:18.277

2

You can use

^(?!0$)\d+(?:[,.][05])?$

See demo

This will match your required numbers and will exclude a 0-only number thanks to the look-ahead at the beginning.

Main changes:

\d+ - replaced [1-9]\d* to allow a 0 as the integer part
[,.] - replace \. to allow a comma as a decimal separator.
The lookahead adds a 0-number exception.

The lookahead can be enhanced to disallow 0.000-like input:

^(?!0+(?:[,.]0+)?$)\d+(?:[,.][05])?$

See another demo.

edited Nov 12 '15 at 18:01

answered Nov 12 '15 at 17:49

Wiktor Stribiżew

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So if I understood correctly: ^(?!0$) ignore number (single) zero – Francisco Ramilo Nov 12 '15 at 17:56
[0-9]\d* what does this mean? – Francisco Ramilo Nov 12 '15 at 17:57
(?:[,.][05])?$ optional but I think that states accept commas and point followed by zero or five – Francisco Ramilo Nov 12 '15 at 17:58
Yes, the lookahead will add an exception to the whole input. `(?!0$)` will disallow `0`, or `(?!0+$)` will disallow `0000`. I have updated the regex, I guess the integer part must be at least 1 digit, right? Please check the [latest demo](https://regex101.com/r/iJ6dY5/6). – Wiktor Stribiżew Nov 12 '15 at 17:59
I see it works for you, great. The lookahead is a negative one, that is why the decimal point/comma and 0 or 5 cannot be accepted. – Wiktor Stribiżew Nov 12 '15 at 18:04

score 0 · Answer 2 · answered Nov 12 '15 at 17:49

0

You can use this regex:

^(?:5|[1-9]\d*[05])(?:[,.][05])?$

RegEx Demo

answered Nov 12 '15 at 17:49

anubhava

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Bohemian · Answer 3 · 2015-11-12T18:06:11.377

0

This should do it:

^(?!0*$)0?\d*([,.]5)?$

See live demo.

This uses ^\d*([,.]5)?$ to match what you want, and uses ^(?!0*([,.]0*)?$) to exclude zero in all its forms, ie it won.t match 0, 000 etc

edited Nov 12 '15 at 18:06

answered Nov 12 '15 at 17:59

Bohemian

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Regex expression to match equal or greater than 0,5 or 0.5, by increments of .5

3 Answers3