Unexpected substitution behavior

Question

I need to put a comma between any two digits in a string of digits. For example, I want this

12345678910

to become this

1,2,3,4,5,6,7,8,9,1,0

The approach I took was the following

s/\([0-9]\)\([0-9]\)/\1,\2/g

Strangely enough, the substitution command above when applied to the string in the example gives

1,23,45,67,89,10

If I apply the substitution command once again, it gives what I want. But why just one instance of the command don't work?

The vim version I'm using is

VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Mar 18 2020 18:29:15)

Matt · Accepted Answer · 2020-09-01 05:34:27Z

7

why just one instance of the command don't work?

Obviously, the string is parsed as (12)(34)(56)(78)(91)0 --> 1,2 3,4 5,6 7,8 9,1 0

A possible solution is s/\d\d\@=/\0,/g. See :h /\@=.

answered Sep 1, 2020 at 5:34

Matt

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This \@= thing is very nifty. Didn't know of it, though. Thanks!
– Larara
Commented Sep 1, 2020 at 5:50
Or s/\d\ze./&,/g. A little shorter, maybe a little more efficient (not that one would notice with such small inputs). On the con side, you want to make sure there are only numbers (otherwise s/\d\ze\d/&,/g).
– B Layer
Commented Sep 24, 2020 at 7:15

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