[SOLVED] lookaround in POSIX regex to match all spaces except the last (for gsub)

lookaround in POSIX regex to match all spaces except the last (for gsub)

...freaking out because of this simple problem:

I'm using an Ingest pipeline with the gsub processor to replace all (white)spaces except the last. E.g.:

"hello world regex is fubar " to result in "hello, world, regex, is, fubar"

How can I convert the PCRE syntax (which won't work gsub TRE patterns, as I found out)

"/\s(?=.\S*)/g"

To POSIX, like...

"/[[:space:]](?=.[[:space:]]*)/g"

(only spaces exchanged, not the lookaround)

Edit: As I can only provide the regex in a string, I cannot use another processor than gsub. '\s' or '\S' are apparently marked as "unknown".

Solution

Worked using " +([^ ])" - another solution would be " +(.)". (Both without the double quotes)

with the replacement/substitution string ,$1.

Thanks to Wiktor Stribiżew for pointing this out.

For whatever reason the POSIX literal [:space] does not work, why [[:space:]]+(.) did not work either, even tho it is a correct regex.