Add CLI command (hugo render) for printing the source files in a custom format

[nachtjasmin]

Note: Someone with a better knowledge of the English language should edit this title, its intent isn't that clear right now. Thanks.

Problem

As of today, there's no "official" way for rendering the list of pages in another format as CSV. hugo list all renders all pages just fine, it's just very limited, as there's no configuration for the output, access to the params, etc.

Parsing the CSV is possible, but due to the mentioned problems, not suitable for all solutions.

We can render the pages in any format using resources.FromString and resources.ExecuteAsTemplate as described in the forum. However, this has the downside that we need to generate the whole page, even if we just want a single file. Especially with a lot of pages, image hooks, etc. this can take a lot of time.

Proposal

Other Go-based tools, for example kubectl allow to pass a Go Template string which is used for rendering the output. I'd like to propose such a feature to the Hugo CLI as well. It would allow to render the pages/resources/whatever in any format.

A possible CLI implementation might look like this:

$ hugo render "<some Go Template syntax>"

or

$ hugo render < my-template.tmpl

Scenarios

This is useful for the following scenarios:

Rendering a .htaccess

Contents of htaccess.tmpl:

# Automatic generated .htaccess using Hugo on {{ now }}

{{ range .Site.AllPages -}}
    {{- $p := . -}}
    {{- with .Params.redirect }}
# {{ printf "Redirect %q using .Params.redirect" $p.Title }}
Redirect 301 "{{ $p.RelPermalink }}" "{{ . }}"
    {{ end -}}
    {{- range .Aliases }}
# {{ printf "Redirect %q using aliases" $p.Title }}
Redirect 301 "{{ . }}" "{{ $p.RelPermalink }}"
    {{ end -}}
{{- end -}}

$ hugo render < htaccess.tmpl > .htaccess # renders the .htaccess

Validating that each page has a title

Contents of validate.tmpl:

[
{{ range .Site.AllPages }}
  {{ if (eq .Title "") }}
    {{ errorf "The page %s does not have a title." .File.Path }}
  {{ end }}
{{ end }}
]

$ hugo render < validate.tmpl # returns with failing status code, causing the CI job to fail

Benefits

• Faster rendering of such templates
• No need to generate all images/folders, just the one file, might be combined with --renderToMemory

Risks

I can't see any risks at the moment.

[github-actions]

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