This will scan the string once, with no backtracking:
# Assuming space delimited words and removing duplicates
# not necessarily next to each other
my $str = "abc def abc hello def 123 abc";

my %count;
$str =~ s/((\w+)\s?)/$count{$2}++ ? '' : $1/eg;
print $str,"\n";

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In reply to Re: most efficient regex to delete duplicate words by runrig
in thread most efficient regex to delete duplicate words by Anonymous Monk

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