Re: Regex arithmetic

On Friday, August 4, 2017 at 10:03:16 AM UTC-7, porphyry5 wrote:
> :h submatch( includes
>         Example:
>             :s/\d\+/\=submatch(0) + 1/
>         This finds the first number in the line and adds one to it.
>
> Needing to increment several fields consisting of underscore and a single digit (_\d) I modified the above along the lines of
>
>       s/_\(\d\)/\='_'.submatch(1) + 1/gc
>
> most of which merely replaced the entire field with '1'
>
> Thinking the problem might be a conflict between the types, string and number, I tried
>
>     s/_\(\d\)/\="_".nr2char(submatch(1) + 1)/gc
> then
>     s/_\(\d\)/\="_".nr2char(submatch(1) + 31)/gc
> and finally success with
>     s/_\(\d\)/\="_".nr2char(submatch(1) + 49)/gc
> which is limited to operations on just a single digit.
>
> So, is there a generally reliable method of performing arithmetic on numeric fields embedded in a larger string pattern with :s? Thank you.
>
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> --
>
> Graham Lawrence

Thank you,
s/_\(\d\)/\='_'.(submatch(1)+1)/g
works perfectly, and I see what I was trying initially
s/_\(\d\)/\='_'.submatch(1)+1/g
is actually equivalent to
s/_\d/\=submatch(0)+1/g

In the meantime, I read :h substitute( and found
s/_\(\d\)/\=substitute(submatch(0),'\d',submatch(1)+1,'')/g
which avoids the problem by making a secondary pattern selection of the number alone. But that's more typing, so I will pay attention to operator precedence in future.

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