PHP particular regular expression

Question

I am trying to target only digits that follows non-numeric characters in a string to add some html tags around them. For the moment i am able to do it on every digit like this :

$string = preg_replace('/(\d+)/','<sub>\1</sub>', $string );

How can i do to just target digits that follows non-numeric characters ? The goal is to format strings containing chemical formulas but not the text around it.

Actually 20% O2 in N2 becomes 20% O2 in N2

I would like it to be 20% O2 in N2 instead.

How can i do this? Is it possible?

Thank you very much for your help

Try preg_replace('/\B\d+|\d+\B/','$0', $string ) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Feb 14, 2017 at 13:16
Another idea: '/\b\d+\b(*SKIP)(*F)|(\d+)/' that can be used in your code as is. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Feb 14, 2017 at 13:19
@WiktorStribiżew your first one won't fail properly on double-or-more digit numbers. — Sebastian Proske
– Sebastian Proske, Commented Feb 14, 2017 at 13:20
@SebastianProske: I know it won't work in many situations. OP requirements are not that clear since a space is also a non-numeric char. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Feb 14, 2017 at 13:21

bobble bubble · Accepted Answer · 2017-02-14 13:52:28Z

4

How can i do to just target digits that follows non-numeric characters ?

For digits that follow letters try with a lookbehind.

(?<=[A-Za-z])\d+

See demo at regex101 (and replace with \0)

For unicode letters use \pL instead of [A-Za-z] together with u flag.

edited Feb 14, 2017 at 13:52

answered Feb 14, 2017 at 13:29

bobble bubble

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5 Comments

bobble bubble Over a year ago

You're welcome @Kamzz! Here a PHP demo at eval.in

Wiktor Stribiżew Over a year ago

So, the question was about how to change the digits after an ASCII letter. '~[A-Za-z]\K\d+~' will also work.

Walter Tross Over a year ago

@WiktorStribiżew I have never seen that \K before, could you please provide a reference (if possible in www.regular-expressions.info)?

Wiktor Stribiżew Over a year ago

@WalterTross: See SO regex documentation. Also, see the Resetting the match start section at pcre.org.

bobble bubble Over a year ago

@WalterTross There's also a nice chapter on rexegg about \K if you're interested. On regular-expressions.info you can read here.

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