$ perl -MO=Concise,-exec -E'my $foo = "weird123"; say $foo . do { $foo =~ s/123//; $foo };'
...
6  <;> nextstate(main 49 -e:1) v:%,{,469764096
7  <0> pushmark s
8  <0> padsv[$foo:47,49] s
9  <0> enter s
a  <;> nextstate(main 48 -e:1) v:%,{,469764096
b  <0> padsv[$foo:47,49] sRM
c  <$> const[PV ""] s
d  </> subst(/"123"/) vKS
e  <;> nextstate(main 48 -e:1) v:%,{,469764096
f  <0> padsv[$foo:47,49] s
g  <@> leave sKP
h  <2> concat[t2] sK/2
i  <@> say vK
...

##</code><code>##

use feature qw( say );
use Data::Alias qw( alias );

sub concat { my $lhs = shift; my $rhs = shift; $lhs . $rhs }

{
   my $foo = "weird123";
   alias push @_, $foo;
   $foo =~ s/123//;
   alias push @_, $foo;
   alias push @_, &concat;
   say shift(@_);
}

##</code><code>##

$ perl -MO=Concise,-exec -E'my $foo = "weird123"; say $foo . "" . do { $foo =~ s/123//; $foo };'
...
6  <;> nextstate(main 49 -e:1) v:%,{,469764096
7  <0> pushmark s
8  <0> padsv[$foo:47,49] s
9  <$> const[PV ""] s
a  <2> concat[t2] sK/2
b  <0> enter s
c  <;> nextstate(main 48 -e:1) v:%,{,469764096
d  <0> padsv[$foo:47,49] sRM
e  <$> const[PV ""] s
f  </> subst(/"123"/) vKS
g  <;> nextstate(main 48 -e:1) v:%,{,469764096
h  <0> padsv[$foo:47,49] s
i  <@> leave sKP
j  <2> concat[t3] sKS/2
k  <@> say vK
...

##</code><code>##

use feature qw( say );
use Data::Alias qw( alias );

sub concat { my $lhs = shift; my $rhs = shift; $lhs . $rhs }

{
   my $foo = "weird123";
   alias push @_, $foo;
   alias push @_, "";
   alias push @_, &concat;
   $foo =~ s/123//;
   alias push @_, $foo;
   alias push @_, &concat;
   say shift(@_);
}