skfold - one-off files


skfold supports generating one-off files in addition to more structured directories.

One of the issues I planned to address with skfold was generating kick-start files for dibs.

To some extent, this is somehow the contrary of what we saw up to now:

  • generation of a single file instead of a new, stand-alone directory
  • choice of one single template out of - possibly - many similar ones.

The second bullet can be easily addressed by having separate modules for each dibs template, but leveraging a single one was really simple and actually didn’t require any specific support/change in skfold, so why not?

The dibs module

The dibs module for skfold is available on GitHub, let’s take a quick look.


There are two templates, at least as of now. One is for a full-fledged Perl application, with its own base images for fine control over caching; the other one is to build quick applications, possibly just based on a few system packages.

As in the rest of skfold, these are actually Template::Perlish templates.

Configuration file

The configuration file for the dibs module has a few options that can be provided on the command line (or set in the main defaults.json file for skfold. Nothing really fancy here, except maybe option templates|T that is marked as being meta. This means that, when present, this option overrides the regular check on mandatory variables, because this option will actually be used to generate a list of template files that are available through this module, hence the other options are not really needed.

Another peculiarity is the option single-file, set at the top level. This indicates to skfold that we don’t expect to have a directory generated in this case, just a single file. Additionally, this also means that this generated file might be specified as going to -, which means that it will be printed on the standard output.

Last, the files section is in this case only used to set the mode. The source template will be chosen differently (we will look at it shortly) and the destination file is, of course, to be determined dynamically.


The customization Perl module includes the following extension function adapt_module_configuration (see also skfold - repeated files).

 1  sub adapt_module_configuration {
 2     my ($config) = @_;
 4     return _templates_list($config) if $config->{opts}{templates};
 6     my $source = $config->{opts}{template};
 7     main::LOGDIE "select one template with -t (call with -T for list)"
 8        unless defined $source;
10     my $spec = $config->{files}[0];
11     my ($target, @files);
12     if ($config->{target} eq '-') {
13        $target = '-';
14     }
15     else {
16        $target = path($config->{target})->absolute;
17        @files = map {
18           my %record = (destination => $_);
19           $record{mode} = $spec->{dmode} if defined $spec->{dmode};
20           \%record;
21        } ancestors_for($target);
22     }
23     push @files, { %$spec, destination => $target, source => $source };
24     $config->{files} = \@files;
26     $config->{target_dir} = path('/');
28     return;
29  };

As anticipated, the whole logic of selecting one single template has been moved into the customization module (line 6 gets the actual source to use from the command line, then line 23 sets this template as the source that will be used by skfold). This is good because it does not need to require any specific support from skfold and somehow makes me confident that it’s already providing what’s needed at the base level.

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