See perlre. It notes that
\G Match only where previous m//g left off (works only with /g)
Try the following: 
perl -e "$num = \"0000012345\"; $num =~ s/\G0/ /g;print $num"

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Cheers,
Ovid

Update: Just saw merlyn's response and wanted to note that I have Effective Perl Programming. Where the heck do you think I got that regex? :)

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In reply to (Ovid) Re: Regex to zero suppress by Ovid
in thread Regex to zero suppress by Theodorus

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