Here is my code.

The problem is that your code does not compile under strictures (the  use strict; statement; see strict). If  use strict; is left out and the code is run under warnings alone (the  use warnings; statement), Perl produces a bunch of warnings about uninitialized values and possible typos, warnings you should ponder well. Also take a look at the rules for interpolation discussed in the Quote and Quote-like Operators section of perlop; a careful Reading of this section of The Fine Manual would repay your effort. (Same as  perldoc perlop from the command line.)

Here is an example of double-quote interpolation and single-quote non-interpolation. (These examples have been given before by others.) An example is also given of entering a string from the command line at a prompt. Note that once successfully entered, 'interpolating' characters do not interpolate further: Perl does not do multi-level or nested interpolation. Perhaps you can build on something like this example to demonstrate the problem(s) you are facing. (Note: I use  qq{double quotes} rather than  "double quotes" on my Windoze command line so that the code will not be cluttered by irruptions of backslashes.)

>perl -wMstrict -le
"my $def = 'hi there';
 my @jkl = qw(foo bar);
 ;;
 my $str1 = qq{abc$def};
 my $str2 = qq{ghi@jkl};
 ;;
 print qq{str1: :$str1:};
 print qq{str2: :$str2:};
 ;;
 my $str3 = 'pqr$def';
 my $str4 = 'xyz@jkl';
 ;;
 print qq{str3: :$str3:};
 print qq{str4: :$str4:};
 ;;
 ;;
 print 'enter password: ';
 my $pw = <STDIN>;
 chomp $pw;
 ;;
 print qq{pw: :$pw:}
"
str1: :abchi there:
str2: :ghifoo bar:
str3: :pqr$def:
str4: :xyz@jkl:
enter password:
open@sez$me
pw: :open@sez$me:
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