Hi Monks,
pls help me check this issues: E.g:

$d = "123456789";
$d =~ s/(?<=\d)(?=(\d\d)+$)/-/g;
print  "$d";
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It produce "1-23-45-67-89" ,it is OK.
But on the contrary,I wanna get a "left-to-right" substitution.That is ,i want to get "12-34-56-78-9"
I try :

$d =~ s/(?<=^(\d\d)+)(?=\d)/-/g;
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It can't work.Where does it wrong? The wrong log:

 
Variable length lookbehind not implemented in regex; marked by <-- HER
+E in m/(?<=^(\d\d)+)(?=\d) <-- HERE / at Noname1.pl line 4.
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TIA.
Pysome