RegEx Expression /w limited length and chars

Question

My question is NOT similiar to Regular expression to match numbers between 1-5000, because I have something else to check (no range, leading and no leading zeroes, etc.).

I have the following RegEx in an input check:

^[0-9]{1,4}$

This works for digits with 1-4 length.

Unfortunately I have to allow only these combinations:

One digit numbers 1-9 (no leading zeroes)
or two digits numbers 10-30 (no leading zeroes)
or four digits numbers 0001-9999 (with leading zeroes).

What RegEx do I need?

You need the or operator, |. Something like ^([0-9]{1,4}|foo|bar)$, where foo is two digits numbers 10-30 (no leading zeroes), and bar is four digits numbers 0001-9999 (with leading zeroes). If you could write the regex you've got, you can write those -- the | operator is all you're missing. — 15ee8f99-57ff-4f92-890c-b56153
– 15ee8f99-57ff-4f92-890c-b56153, Commented Oct 27, 2016 at 14:15
Try ^([1-9][0-9]?|[0-9]{4})$. I guess you need to skip the numbers from 100 to 999 altogether, right? And does 10-30 range is just an example, and you want the 2-digit numbers from 10 to 99 or really only up to 30 only? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Oct 27, 2016 at 14:16
Possible duplicate of Regular expression to match numbers between 1-5000 — Thomas Ayoub
– Thomas Ayoub, Commented Oct 27, 2016 at 14:26

Wiktor Stribiżew · Accepted Answer · 2016-10-27 14:26:08Z

Let's define subpatterns for your conditions:

One digit numbers 1-9 (no leading zeroes) - Use [1-9]
or two digits numbers 10-30 (no leading zeroes) - Use [12][0-9]|30
or four digits numbers 0001-9999 (with leading zeroes) - Use [0-9]{4}

So, the whole pattern should be built from those alternatives that should be anchored and grouped (so that the anchors were applied to the group)

^([1-9]|[12][0-9]|30|[0-9]{4})$

See the regex demo

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