LibreOffice Calc »regex« function – which regex format is applicable?

Question

I want to find a string like a DOI in a sentence and extract the result in a cell. I found the »regex« function in LibreOffice Calc (current Ver. 6.2.4.2) which tells me that it would exactly do what I want.

Example:

Foo bar doi: 10.1016/j.cmpb.2018.09.006 baar foooo

My regex in python is: \b(10[.][0-9]{4,}(?:[.][0-9]+)*\/(?:(?![\"&\'<>])\S)+)\b and suits me well in a python script (it matches exactly the doi number without the »doi« string, which is intended).

But the »regex« function refuses this regex. The documentation mentions the ICU Regex Expressions, where I can't find any issues comparing with my regex.

Do I miss something? Which »regex dialect« is applicable for LibreOffice?

Answer 1

In the list of regular expressions supported by LibreOffice, most of the standard expressions are supported, but two of the elements you use are missing:

1. the use of ?: for a non-capturing group;

2. the use of ?! for a negative look-ahead.

                     1              1  2
                     |              |  |
                     v              v  v
   \b(10[.][0-9]{4,}(?:[.][0-9]+)*/(?:(?!["&'<>])\S)+)\b
   

I don't know what level of RE this represents (it seems to be BRE with additions), but it means that your RE won't match your test string.

It is not clear how much of your string constitutes the number you are trying to isolate, so I cannot suggest how you might avoid the unsupported elements, but these are a couple of possibilities:-

• If you need the numeric string between doi: and /, then the simpler \b10[.][0-9]{4,}(?:[.][0-9]+)* will suffice.
• If you need everything between doi: and the next space, then you can use \b10[.][0-9]{4,}(?:[.][0-9]+)*[^\s]*.

(This second case gives the same match as your RE on RegExr.)

I realise that your live data may have more exceptions that must be caught, but without a full knowledge of your data and the number you are trying to match I cannot do more.