#!/usr/bin/perl
use v5.14;

my %cfg = (
    tmpl_path   => $ENV{HOME}.'/.skel-closet/',
    opening_tag => '#{',
    closing_tag => '}',
);

sub prompt {
    my $msg = shift;

    local $| = 1;
    local $\;
    warn "$msg \n";

    my $ans = <STDIN>;
    defined $ans ? chomp $ans : warn "\n";
    return $ans;
}

sub filled_line {
    my $line = shift;
    my $pattern = qr/$cfg{opening_tag}(.+?)$cfg{closing_tag}/;
    $line =~ s/$pattern/$ENV{$1} ? $ENV{$1} : prompt("$1 unset. Value:") /eg;
    return $line;
}

my $filename = $cfg{tmpl_path}.shift;

open (my $fh, '<', $filename)
    or die ("Could not open file: $filename");

my @output;
while (<$fh>) {
    push @output, filled_line($_);
}
close ($fh);

print for @output;

##</code><code>##

$ cat ~/.skel-closet/test
This is the value of HOME: #{HOME}
This is the value of EDITOR: #{EDITOR}
This is the value of FOO: #{FOO}

$ ./pskel.pl test > out.txt 
FOO unset. Value: 
foovalue

$ cat out.txt 
This is the value of HOME: /home/blj
This is the value of EDITOR: emacs
This is the value of FOO: foovalue