$ perl -wE ' my $remove = q{foo}; my $str = q{barfoobaz}; say $str =~ s/$remove//;'
1

$ perl -wE ' my $remove = q{foo}; my $str = q{barfoobaz}; ( my $x = $str ) =~ s/$remove//; say $x;'
barbaz

$ perl -wE ' my $remove = q{foo}; my $str = q{barfoobaz}; say $str =~ s/$remove//r;'
barbaz