How can I write a regex that limits user input to 3 digits in the range of 0-128?

I've been trying \d{1,3} but this allows for a match more than the 0-128 range.

Thanks

How can I write a regex that limits user input to 3 digits in the range of 0-128?

I've been trying \d{1,3} but this allows for a match more than the 0-128 range.

Thanks

• javascript
• regex

Share Improve this question Follow edited Mar 2, 2015 at 19:16 willeM_ Van Onsem 479k3333 gold badges476476 silver badges614614 bronze badges asked Mar 2, 2015 at 18:51 JakeJake 26.1k3131 gold badges114114 silver badges178178 bronze badges 4

• Why should this be a RegEx? – thefourtheye Commented Mar 2, 2015 at 18:54
• cuz it's easy to check than me doing if else loops later on. – Jake Commented Mar 2, 2015 at 19:02
• 1 if (parseInt(value, 10) >= 0 && parseInt(value, 10) <= 128)? – thefourtheye Commented Mar 2, 2015 at 19:03
• 1 agreed.. but what I am doing will go with a regex, that I already have in place. The question here is just a piece of that puzzle. :) appreciate the answer though. – Jake Commented Mar 2, 2015 at 19:12

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4 Answers 4

Sorted by: Reset to default 5

You can use this regex:

/\b([0-9]{1,2}|1[01][0-9]|12[0-8])\b/

Use this utility

Excluding 128

You can do this using the following regex:

^0?\d{1,2}|1([0-1]\d|2[0-7])$

You more or less break it down hierarchically.

The first:

0?\d{1,2}

captures all values up to (and including) 99, optionally with a leading zero (so 064) is accepted.

Next you capture 1[0-1]\d. These are the values 100 to 119. This is because there is no constraint on the last digit.

And finally you have 12[0-7], the two first digits are fixed, and you can use 120 up to 127.

Including 128

In case 128, is allowed as well, use:

^0?\d{1,2}|1([0-1]\d|2[0-8])$

Leading zeros not allowed

The you can use:

^\d|[1-9]\d|1([0-1]\d|2[0-8])$

Word boundaries

Here I've added the ^ and $ so that the string begins and ends with the number. Otherwise, you can use - as @anubhava suggests - word boundaries \b. Although one probably better uses:

\b(0?\d{1,2}|1([0-1]\d|2[0-7]))\b
\b(0?\d{1,2}|1([0-1]\d|2[0-8]))\b
\b(\d|[1-9]\d|1([0-1]\d|2[0-8]))\b

Regex is the wrong tool for the job.

<input type="number" min="0" max="128" />

Done.

0 - 128 would be: ^(?:\d|[1-9]\d|1[0-1]\d|12[0-8])$

^
(?:
     \d
  |  [1-9] \d
  |  1 [0-1] \d
  |  12 [0-8]
)
$