Validate rating variable, Before processing - php

Question

I have a rating variable that is sent to PHP using Ajax, I want to validate that variable.
The rating starts from 0.5 to 5, So the possible accepted values would be 0.5, 1, 1.5, 2, .. 5.
I'm trying to check it using Regular Expressions:
$var = 0.5;
$pattern = '/^[0-9]|[0-9.][0-9]$/';
if( ! preg_match($pattern, $var) ){
echo 'Doesn't match!';
}else{
echo 'Matches!';
}
But that would check any number, Or decimal like 1, 0.2, 10000, 1000.99.
So how to limit that to check only if it's 0.5, 1, 1.5, .. 5?

Answer 1

Just look for numbers 0-4 and the optional .5, or a 5.
^(?:[0-4](\.5)?|5)$
Demo: https://regex101.com/r/Bcsl6d/1/
...or if 0 is not valid, do the same as we did with 5.
^(?:0\.5|[1-4](\.5)?|5)$
Explanation:
Your regexs:
^[0-9]|[0-9.][0-9]$
^[1-9]|[1-9.][1-9]$
are just looking for a number numbers, or a number or . and a number. You need the . outside the character class an to be optional, then you need the number after the . to only be a 5 and also optional. The 0-9 also is too large, you really want 1-5, but you can't do an optional .5 after that range because it would make 5.5 valid.
You also could just the 2 PHP functions for this range and in_array. The third parameter of range is the step to increase the values by.
$values = range(.5, 5, .5);
if(in_array('5', $values)) {
echo 'valid number';
} else{
echo 'invalid';
}
https://3v4l.org/1LfAT

Answer 2

Or since you just have ten possible values, for all those who have to look at the code later and actually attempt to make sense of it:
$valid = ['0.5', '1', '1.5', '2', ...];
if (!in_array($var, $valid)) {
// invalid value given.
}
There is no need to use a convoluted regular expression to validate something so simple.

Answer 3

You may use this regex to match numbers from .5 to 5 with trailing .0 as optional e.g. 4.0 and 4 both will be validated:
^(?:[1-4](?:\.[05])?|0?\.5|5(?:\.0)?)$
RegEx Demo
RegERx Details:
^: Start
(?:: Start non-capture group
[1-4](?:\.[05])?: Match numbers from 1.0 to 4.5 with trailing .0 optional
|: OR
0?\.5: Match 0.5 or .5
|: OR
5(?:\.0)?: Match 5 or 5.0
): End non-capture group
$: End