Win8 Strawberry 5.8.9.5 (32)  Fri 11/06/2020 18:48:09
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings
use Data::Dump qw(pp);

my $linkheader = 'axbyczSelfaxbycz';
printf "A: '$linkheader' (\$1 is %s) \n", pp $1;

(my $link1 = $linkheader) =~ s/ .*? (Self)/$1/gx;
printf "B: '$link1' (\$1 is %s) \n", pp $1;

(my $link2 = $link1) =~ s/a/$1/g;
printf "C: '$link2' (\$1 is %s) \n", pp $1;

^Z
A: 'axbyczSelfaxbycz' ($1 is undef)
B: 'Selfaxbycz' ($1 is "Self")
Use of uninitialized value in substitution iterator at - line 9.
C: 'Selfxbycz' ($1 is undef)