Complex regex with hexadecimal part

Question

I need to write a regex that matches the string:

HELLO[ID]_world.NNN

Where:

'HELLO' is constant. It must always start with this word
'ID' is any number
'world' is anything
'NNN' is the sequence number in hexadecimal notation, i.e. '000' to 'FFF'

For example valid strings are:

HELLO[345]_something.123
HELLO[23]_BlaBla.FFF

What I have so far is:

\bHELLO\[[0-9]*\]_[a-zA-Z]*\.[0-9]{3}

If I am correct (and maybe I am not) this works for all examples except hexadecimal part.

Could you help me to write this regex?

You say *`'world' is anything`* but you use `[a-zA-Z]*` that only matches letters. Try [`\bHELLO\[[0-9]*]_\S*\.[a-fA-F0-9]{3}\b`](https://regex101.com/r/H77hjv/2/) If you need to only match *entire* strings, replace [`\b...\b` with `^...$`](https://regex101.com/r/H77hjv/3). — Wiktor Stribiżew, Sep 04 '18 at 13:16
Also consider using `+` instead of `*` if you don't want to match `HELLO[]_.123` — Aaron, Sep 04 '18 at 13:17
[`\bHELLO\[[0-9]+\]_[a-zA-Z0-9]+\.[a-zA-Z0-9]{3}`](https://regex101.com/r/nEkeBY/1) — Sagar V, Sep 04 '18 at 13:20

score 1 · Accepted Answer · answered Sep 04 '18 at 13:22

To match hexadecimal numbers, you just have to add a-f and/or A-F to the [0-9]{3} group, depending on whether you want to match upper- or lowercase hex numbers or both.

Also, as noted in comments, you might want to change the * to + to disallow empty strings for those parts.

HELLO\[[0-9]+\]_[a-zA-Z]+\.[0-9a-fA-F]{3}

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Complex regex with hexadecimal part

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