#!/usr/bin/perl 
use warnings; 
use strict; 
 
my $var = 'foo'; 
undef $/; 
my $data = <DATA>; 
$data = eval {$data}; 
print $data; 
 
 
__DATA__ 
hello $var

#!/usr/bin/perl 
use warnings; 
use strict; 
 
my $var = 'world'; 
 
undef $/; 
my $data = <DATA>; 
 
$data =~ s/(\$\w+)/$1/eeg; 
 
print $data; 
 
__DATA__ 
hello $var

my $var = 'numb nuts'; 
my $data = join '', <DATA>; 
my $string = sprintf($data, $var); 
 
__DATA__ 
Hello %s

#!/usr/bin/perl 
use warnings; 
 
#make sure we can't use symbolic refs :-) 
use strict; 
  
#here is where we assign a value to $var or 'define' it as you say 
my $var = 'world'; 
  
#read in the contents of the file and store it *as a string* in $data 
#note, I only use the DATA filehandle for simplicity, 
#could be any file 
undef $/;  
my $data = <DATA>;

#originally I thought an eval would cause interpolation 
#but it doesn't in this case 
#however, match and substitute *do* interpolate,  
#thus replacing the scalars with themselves, we get interpolation 
$data =~ s/(\$\w+)/$1/eeg;  
  
#prints hello world 
print $data;  
  
__DATA__  
hello $var

#!/usr/bin/perl  
use warnings;  
use strict;  
  
my $var = 'world'; #hopefully no questions here 
  
my $string = 'hello $var';#just a plain old string. agreed? 
 
undef $/;  
my $data = <DATA>;  
 
#Q: what's the difference between what's in $data and $string now? 
#A: Nothing! 
 
#oops, I really wanted interpolation on that single quoted string 
#I'll follow Tom Christiansen's advice from perlfaq4: 
$data =~ s/(\$\w+)/$1/eeg;  
  
print $data;  
#woopie!! I'm done!! 
 
$string =~ s/(\$\w+)/$1/eeg;  
print $string; #same thing 
 
__DATA__  
hello $var