^ in FS

[Dave B]

I'm having trouble in understanding the behavior of ^ in FS, although I
don't know whether it can be called "bug". Some examples follow (gawk 3.1.6).


$ echo '  f1 ,  f2,f3  ,  f  4  ,f5' | awk -v FS='^ *| *, *'
'{for(i=1;i<=NF;i++)print "-->"$i"<--"}'
--><--
-->f1<--
-->f2<--
-->f3<--
-->f<--
-->4<--
-->f5<--

The above FS matches the spaces at the beginning as expected, but
unexpectedly also matches the spaces between "f" and "4". Other
implementations of awk output

--><--
-->f1<--
-->f2<--
-->f3<--
-->f  4<--
-->f5<--

which makes more sense to me.

But if I change FS to FS='^ +| *, *', then gawk works as expected:

$ echo '  f1 ,  f2,f3  ,  f  4  ,f5' | awk -v FS='^ +| *, *'
'{for(i=1;i<=NF;i++)print "-->"$i"<--"}'
--><--
-->f1<--
-->f2<--
-->f3<--
-->f  4<--
-->f5<--

Also note that the issue seems related to ^ only, since using FS=' *$| *,
*', with an input of 'f1 ,  f2,f3  ,  f  4  ,f5  ' (spaces at the end)
produces (correctly imho)

-->f1<--
-->f2<--
-->f3<--
-->f  4<--
-->f5<--
--><--

Not sure I completely understand what's going on there.
Thanks for any elucidation.

-- 
D.