How can I create a regex that allows whole numbers, decimals, fractions, and fractions with decimals? The string can also have optional text, only at the end. So far I have this:
JavaScript
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const re = /^d*.?d*/?d*.?d*[a-z]*$/gi;2
This allows double decimals in a whole number(ie: ‘23.23.23’), which I do not want. Can I modify this regex to allow two decimal points only if it is separated by a ‘/’?
Here are some examples that can pass:
- 23.23/100km
- 1/3
- .23km
- 1.mi
- 1.2/2.1kg
Some examples that shouldn’t pass:
- 1a3km
- 12.12.12
- 1.2.3/12.13km
- 12km/12.44km
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Answer
Use
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^(?!.*d+(?:.d+){2})d*.?d*/?d*.?d*[a-z]*$2
See proof. This expression disallows three numbers that have a period between one another thanks to (?!.*d+(?:.d+){2}) negative lookahead.
EXPLANATION
JavaScript
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^ the beginning of the string3
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(?! look ahead to see if there is not:5
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.* any character except n (0 or more times7
(matching the most amount possible))8
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d+ digits (0-9) (1 or more times (matching10
the most amount possible))11
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(?: group, but do not capture (2 times):13
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. '.'15
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d+ digits (0-9) (1 or more times17
(matching the most amount possible))18
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){2} end of grouping20
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) end of look-ahead22
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d* digits (0-9) (0 or more times (matching24
the most amount possible))25
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.? '.' (optional (matching the most amount27
possible))28
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d* digits (0-9) (0 or more times (matching30
the most amount possible))31
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/? '/' (optional (matching the most amount33
possible))34
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d* digits (0-9) (0 or more times (matching36
the most amount possible))37
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.? '.' (optional (matching the most amount39
possible))40
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d* digits (0-9) (0 or more times (matching42
the most amount possible))43
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[a-z]* any character of: 'a' to 'z' (0 or more45
times (matching the most amount possible))46
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$ before an optional n, and the end of the48
string49