Please check: http://perldoc.perl.org/perlop.html#Regexp-Quote-Like-Operators

if (1)
 {my $data = "this is a test";
  my $expression_text = "(.*)es";
  $data =~  $expression_text;  say "1: $1";
  $data =~ /$expression_text/; say "2: $1";
 }
if (1)
 {my $data = "this is a test";
  my $expression_text = qr(es);
  $data =~  $expression_text;      say "3: $data";
  $data =~ s/$expression_text/dd/; say "4: $data";
 }
[download]

Produces

1: this is a t
2: this is a t
3: this is a test
4: this is a tddt