Minimal, %ENV based templating tool

[blindluke]

There is a nice, minimal templating tool out there, called skel. Its author, Scott Vokes, describes it as a "tiny command-line skeleton/snippet thing", and it's probably accurate.

Given a template file name, it expands all the occurences of #{VARIABLE} with the value obtained from the %ENV.

The tool has proven quite useful to me, mostly due to the way it provides a lot of useful features while still allowing you to use it in the most primitive way imaginable.

Inspired by the simplicity of it, I tried rewriting the most basic version of the idea in Perl, adding the one (the only?) feature I was missing - asking for variable values when the ENV var is unset.

#!/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;

The use is straightforward. Here's an example:

$ 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

[u65]

Nice improvement, Luke. You should submit a pull request.

[blindluke]

Thank you.

The skel tool is written in C and, on top of the simple core idea, it offers a lot of small additional features, like lowercase/uppercase conversion and support for default values. My script could hardly be considered an improvement over the original - but it could complement it, when you need just the core functionality and the one feature I've added.

I could try to port this feature to the original, as I would be happy to contribute to a tool I use, but I'm not sure if my C skills are up to it. But I will still fork it and try, if time allows.

Just for completeness sake, here is my initial version with just the core functionality:

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

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

sub filled_line {
    my $line = shift;
    my $pattern = qr/$cfg{opening_tag}(.+?)$cfg{closing_tag}/;
    $line =~ s/$pattern/$ENV{$1}/g;
    return $line;
}

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

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

print filled_line($_) while (<$fh>);
close ($fh);

Not much use for it over the version I posted earlier, but it shows the one thing that still bugs me. The sub is called filled_line, because I knew I wanted a nice sounding noun for the print filled_line expression. With the switch to buffering in the second version, this nice sound of the penultimate line was unfortunately lost - I could not push filled_line($_) to @output, because push does not work that way.

Someone might say that this is completely irrelevant, but the way I see it, if I did not care about the way those lines sound, I would not be so attached to Perl.