sub safeswitch {
        my @P = (undef,$1,$2,$3,$4,$5,$6,$7,$8,$9);
        $_[0] =~ s/\$(\d)/$P[$1]/g;
        $_[0];
}

my $str = "abcdefghijafjafjkagjakg";

my $pat = '(a.)';
my $repl = '$1 ';

$str =~ s/$pat/safeswitch($repl)/eg;

print $str,$/;