Clash Royale CLAN TAG#URR8PPP

Regex for whole numbers or numbers with quarter decimal

I need a regex that only allows for whole numbers or numbers with a quarter decimal.

So far I have this, however this code /[^.]+.25|[^.]+.50|[^.]+.75|[^.]+.00/ forces user to type a number with a decimal. I'm looking for something more flexible.

/[^.]+.25|[^.]+.50|[^.]+.75|[^.]+.00/

Valid

0
0.
.25
.5
.75
3
1.


1.00
5.0
4.25
8.50
8.75

Invalid

1.2
.3
.
empty space


^(?!.?$)d*.?(?:[27]5|5?0?)?$

1.00

^(?!.?$)d*.?(?:[27]5|[50]0?)?$

2 Answers
2

You might use an alternation to match either an optional digit followed by a dot the quarter decimal part or match one or more digits followed by an optional dot.

^(?:d*.(?:[27]5|50?|00?)|d+.?)$

^(?:d*.(?:[27]5|50?|00?)|d+.?)$

Explanation

(?:

d*.

(?:[27]5|50?|00?)

|

d+.?

)

$

Here's one way:

/A (?= .? [0-9] ) [0-9]* (?: . (?: [05]0? | [27]5 )? )? z/x


Or with comments:

/
A # beginning of string

(?= # look-ahead
.? # a dot (optional)
[0-9] # a digit
)
# ^ this part ensures that there is at least one digit in the string.
# in the following regex all parts are optional.

[0-9]* # the integer part: 0 or more digits
(?: # a group: the decimal part
. # a dot
(?: # another group for digits after the decimal point
[05]0? # match 0 or 5, optionally followed by 0 (0, 00, 5, 50)
|
[27]5 # ... or 2 or 7, followed by 5 (25, 75)
)? # this part is optional
)? # ... actually, the whole decimal part is optional

z # end of string
/x


It's a bit tricky because all parts of the number are optional in some way:

.25

0

0.

The main regex is written in a way that makes all parts optional, but there's a look-ahead assertion before it to make sure that the whole string is not empty or just ..

.

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