Regex matching one or more digits or a Roman number from I to X after word with certain prefix

Question

I want to match a number placed at the end of a string or maybe the middle.

The example would be:

"chapter some word 12 or IV" or "chapter some word 12 or IV some word"

the number what I want to extract is "12" or IV from the string.

I have tried to look around with ?:\w* or ?=\w* but it does not work.

My regex:

if (preg_match('/ch\w*\s*\K(?|(?=((?<=|\s)\d+(?:\.\d+)?))|(?=([ivx]+(?![a-z]))))/i', $string, $matches)){
    print_r($matches);
}

Am I missing something with the regex? Any pointers in the right direction would be appreciated.

Wiktor Stribiżew · Accepted Answer · 2019-10-08T07:37:05.210

2

You may use

'~\bch\D*\K\d+~i'

**To match any 1+ digits or Roman numbers from 1 to 10 (I to X) after the word use

'~\bch.*?\K\b(?:\d+|VI{0,3}|I(?:[XV]|I{0,2}))\b~i'

Here, a set of alternatives is added to \d+: VI{0,3}|I(?:[XV]|I{0,2}).

Details

\b - starting word boundary, no letter, digit or _ should appear immediately to the left of the current position
ch - a literal substring
\D* - 0+ non-digit chars
\K - match reset operator
\d+ - 1+ digits
VI{0,3}|I(?:[XV]|I{0,2}) - V and 0, 1, 2 or 3 Is (that is, Roman 5, 6, 7, 8), or I that is followed with X or V (that is, 9 and 4) or with 0 (so, Roman 1 is matched), 1 or 2 Is (Roman 2 and 3).

edited Oct 08 '19 at 07:37

answered Oct 07 '19 at 13:09

Wiktor Stribiżew

Could you do to match roman (ivx only) too? \D* make it don't match any roman number – niznet Oct 07 '19 at 13:20
@niznet Sorry, I think there is too little data: do you mean the Roman numbers as whole words may appear there? In between whitespace or punctuation? – Wiktor Stribiżew Oct 07 '19 at 13:22
@niznet Try `'~\bch.*?\K(? – Wiktor Stribiżew Oct 07 '19 at 13:25
Updated the question. I only need I , V , X (I until X) – niznet Oct 07 '19 at 13:27
1

@niznet From `I` to `X`: `'~\bch.*?\K\b(?:\d+|I{1,3}|IV|VI{0,3}|I?X)\b~i'`. See [this demo](https://regex101.com/r/SEByKM/3). – Wiktor Stribiżew Oct 07 '19 at 13:30

1 Answers1