Does the following help?

use Modern::Perl;
use warnings FATAL => qw{ uninitialized };

my $abc = "ABC";
my $def = "DEF";
## no $ghi is defined.
my $jkl = 0;

my $funnystring = 'hello $abc and $def and $ghi and $jkl';
$funnystring =~ s/(\$\w+)/defined eval $1 ? eval $1 : "unknown $1" /ge
+;
print $funnystring;

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Output:

hello ABC and DEF and unknown $ghi and 0

[download]

Update: Changed from single to double quotes (i.e., "unknown $1") in the ternary operator to show unknown $ghi in output instead of unknown $1.

In reply to Re: super-simple regex-based template eval --- handling undefined substitutions by Kenosis
in thread super-simple regex-based template eval --- handling undefined substitutions by iaw4

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