This code uses a similar technique to that used by the CPAN Acme::EyeDrops module. To illustrate, running this program:

use Acme::EyeDrops qw(sightly);
print sightly({ Regex        => 1,
                Print        => 1,
                Compact      => 1,
                SourceString => "allen\n" });
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produces:

''=~('('.'?'.'{'.('['^'+').('['^')').('`'|')').('`'|'.').('['^'/').'"'
+.('`'|'!').('`'|',').('`'|',').('`'|'%').('`'|'.').('!'^'+').'"'.'}'.
+')')
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which, when run through Deparse, produces:

'' =~ /(?{print"allen\n"})/;
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For more fun, Acme::EyeDrops allows you to pour the generated code into various shapes. For example, running:

use Acme::EyeDrops qw(sightly);
print sightly({ Shape        => 'rose',
                Regex        => 1,
                Print        => 1,
                Indent       => 1,
                SourceString => "allen\n" });
[download]

produces:

                                   ''=~('('.'?'
                                 .'{'.('['^"\+").(
                                '['^')'        ).+(
                               "\`"|   (')')).(  "\`"|
                              '.').  ('['^        '/').
                             "\"".(  '`'|  '!').   ("\`"|
                             ',').  ('`'|  ',').(  ('`')|
                      '%').  ('`'|  '.').(        '!'^'+'
                   ).'"'.'}'. ')');  $:='.'^'~';$~=('@')|
                   '(';$^=')'^'[';$/  ='`'|('.');$,=  '('
                   ^'}';$\='`'|'!';$:   =')'^'}';$~  ='*'
                   |('`');$^=  '+'^'_';    $/='&'   |'@'
                    ;$,='['&'~'  ;$\="\,"^        '|';$:=('.')^
                     '~';$~="\@"|  '(';$^=')'^'[';$/='`'|'.';$,=
                       '('^'}';$\=  '`'|'!';$:=')'^"\}";  ($~)=
                         '*'|'`';$^  ='+'^'_';$/=('&')|  '@';$,
                           ='['&'~';  $\=   ','^'|';$:  ='.'^'~'
                          ;$~='@'|'('  ;$^=      ')'   ^('[');$/=
                          '`'|'.';$,='('^'}';$\=      '`'|'!';$:=
                          ')'^'}';$~='*'|'`';$^='+'^'_';$/="\&"|
                          '@';$,='['&'~';$\=       ','     ^((
                           '|'));$:=('.')^
                            '~';$~=   '@'
                                      |((
                                     '('
                                     ));
                                     $^=
                ( ')')^'[';         $/=
                ((  '`'))|'.';      $,=
               "\("^  '}';$\='`'   |((
                '!'));  $:=(')')^  '}'
                   ;($~)  ="\*"|  '`'
                     ;($^) =((    '+'
             ))^'_'    ;($/)=  '&'|'@';$,=
          '['&'~';$\=      ','^'|';$:=('.')^
       '~';$~='@'|  '(';$^=')'^  '[';$/=('`')|
     '.';$,='('^  "\}";$\= ('`')|  '!';$:="\)"^
   '}';$~='*'|  ('`');$^=  '+'^'_';  $/='&'|'@'
  ;$,=('[')&  ('~');$\=     ','^"\|";  $:=('.')^
 ('~');$~=  '@'|'(';$^      =')'^'[';$/  =('`')|
 '.';$,=  '('^'}';$\         ='`'|'!';$:  ="\)"^
 '}';$~ ='*'|'`';              $^='+'^'_';  ($/)
 ='&'| '@';$,=                '['  &'~';$\=  ','
 ^'|' ;($:)                   =((   '.'))^'~' ;(
 $~) ='@'                     |((        "\("));
 $^ =((                      ')'
 ))^((                       '['
  ))                         ;$/
                            =((
                            '`'
                            ));
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