First using symbolic references in this way is a hallmark of bad program design. There really is not any good reason to do it the way you are trying to. See this excelent article Why it's stupid to use a variable as a variable name

Anyway it will work if you remove the my declarations as shown:

#!/usr/bin/perl -w

my %userInfo;

$userInfo{fname} = '__fname__';
$userInfo{lname} = '__lname__';
$userInfo{email} = '__fullFrom__ <__email__>';

$fname = 'John';
$lname = 'Doe';
$fullFrom = join(' ', $fname, $lname);
$email = 'john@doe.com';


foreach my $key (keys %userInfo) {
    $userInfo{$key} =~ s/__([^_]+)__/${$1}/g;
    print $userInfo{$key}, "\n";
}
C:\>perl test.pl
Name "main::fullFrom" used only once: possible typo at test.pl line 11
+.
Name "main::email" used only once: possible typo at test.pl line 12.
John
John Doe <john@doe.com>
Doe

C:\>
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print