Re^2: how to search and replace the match with specific number of times in a string

Note that there is a warning (at least as of the current documentation) that the (*ACCEPT) backtracking control verb is "... highly experimental [and] is not recommended for production code."

A slightly different take:

>perl -wMstrict -le
"my $N = 3;
 my $string = 'XXXXXaXXbXXXc';
 $string =~ s{ X (?(?{ $N and $N-- }) | (*FAIL)) }{Xy}xmsg;
 print $string;
"
XyXyXyXXaXXbXXXc
[download]

See Special Backtracking Control Verbs in perlre.

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