It's just a tie.

use strict;
use Tie::File;

# skipping all sorts of fun to get to this:

tie @array, 'Tie::File', "$mf_dir$filename", recsep => '}', autochomp 
+=> 0;

$array[$user_section] =~ s/username =\> $username/username =\> $newuse
+rname/;

# or something like that
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If strict is bothering you :) turn it off :)  no strict 'refs';   ## no critic; because  strict itself confers no benefits; The benefits come from avoidance of the bad practices forbidden by  strict :)

Its time to read a classic :)

Here is explanation of how to do this (  no strict 'refs';   ## no critic; ), why not to do this, and the better approach -- it is FAQ :)

1. Why it's stupid to `use a variable as a variable name'
2. A More Direct Explanation of the Problem
3. What if I'm Really Careful?

But that would only work with GLOBALS (our/vars ) not lexicals (my)

If you want to get at lexicals (my vars) you should use PadWalker

Well because I really don't want to turn strict off since as you point out using a variable as a variable name isn't the best idea. As I mentioned in my post, I'm willing to consider alternatives. I'm just not seeing how to implement the alternatives in my specific case.

Well because I really don't want to turn strict off... strict is lexically scoped, you don't have to turn it off for the whole program

no strict;
if (defined $$newvarname) {
    $$var = $$newvarname;
}
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but that will only work of the vars are our vars

I'm just not seeing how to implement the alternatives in my specific case.

You could improve upon your description ( post a more complete question), I don't see why a hash couldn't work

my %hash = ( qw/ foo 1 bar 2 baz 3 / );

$array[$user_section] =~ s{
    ^ username => (.*) $
}{
    Dance( \%hash, $1 );
}xemg;

sub Dance {
   my( $vars, $one ) = @_;
   my $name = $vars->{$one};
   return "username => $name" if defined $name;
   die "no name for $one ";
}
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I'm just not seeing how to implement the alternatives in my specific case

Well, its difficult to know, since you don't show why you need a bunch of $newfoo variables, but the approach with a hash might be to have two hashes, one for the original vars, and one for the new vars; so something like

use strict;
my %vars = ("foo" => 1, "bar" => 2, "baz" =>3);
my %newvars = ("newfoo" => "A");

foreach my $var (keys %vars) {
  my $newvarname = "new" . $var;
  if (defined $newvars{$newvarname}) {
    $vars{$var} = $newvars{$newvarname};
  }
}
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Dave.

You can't use a string as a reference while strict refs is in use. That's the whole point of strict refs. If you want to use a string as a reference, you should disable strict refs.

no strict 'refs';
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Your question is a bit like asking, "I've put up a sign on my front gate which says 'No Dogs Allowed'. Now I can't let my dog into my garden. How do I let my dog into my garden?"

If you want to use non-strict references, don't put up a sign (use strict) that says only strict references are allowed.

use strict;
use strict;
use warnings;
use Data::Dump qw(pp);

my %oldvalue = (
    foo => "1",
    bar => "2",
    baz => "3"
);

my %newvalue = (
    foo => "A"
);

foreach my $key (keys %oldvalue) {

      if (exists $newvalue{$key}) {
          $oldvalue{$key} = $newvalue{$key};
      }
}

pp \%oldvalue;      # { bar => 2, baz => 3, foo => "A" }
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Or even simpler:

use strict;
use warnings;
use Data::Dump qw(pp);

my %oldvalue = (
    foo => "1",
    bar => "2",
    baz => "3"
);

my %newvalue = (
    foo => "A"
);


%oldvalue = (%oldvalue, %newvalue);
pp \%oldvalue;      # { bar => 2, baz => 3, foo => "A" }
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