How to run a script when the interpreted contents of a template file changes

[rea1shane]

EDITED (To describe the problem more clearly)

Parts of my files tree:

.
└── home
    ├── .chezmoiscripts
    │   ├── darwin
    │   │   └── run_onchange_after_install-packages.sh.tmpl
    ├── .chezmoitemplates
    │   └── homebrew
    │       └── Brewfile_darwin.tmpl
    ├── private_dot_config
    │   ├── homebrew
    │   │   └── Brewfile.tmpl

.chezmoiscripts/darwin/run_onchange_after_install-packages.sh.tmpl:

#!/bin/bash

set -eufo pipefail

# Brewfile hash: {{ include ".chezmoitemplates/homebrew/Brewfile_darwin.tmpl" | sha256sum }}
brew bundle --global

private_dot_config/homebrew/Brewfile.tmpl:

{{- if eq .chezmoi.os "darwin" -}}
{{-   template "homebrew/Brewfile_darwin.tmpl" . -}}
{{- end -}}

You can see that I am now using the hash of .chezmoitemplates/homebrew/Brewfile_darwin.tmpl in the comments. I've tried using the hash of private_dot_config/homebrew/Brewfile.tmpl in comments before, but I've found it to be set in stone.

Is there any way to use the hash of private_dot_config/homebrew/Brewfile.tmpl's interpreted contents?

[bradenhilton]

include will include the literal contents of your template before it is executed. You need to use includeTemplate instead which includes the result of the template.

[halostatue]

I’m not sure why you’re using two templates chained together for this. You may want to use includeTemplate in both places (yes, template by itself should work in most cases, but there are cases when includeTemplate works and template doesn't).

[rea1shane]

Hi @halostatue, you are right. After updating private_dot_config/homebrew/Brewfile.tmpl to:

{{- if eq .chezmoi.os "darwin" -}}
{{-   includeTemplate "homebrew/Brewfile_darwin.tmpl" . -}}
{{- end -}}

Everything's OK now.

I’m not sure why you’re using two templates chained together for this.

I following the docs Use completely different dotfiles on different machines and Run a script when the contents of another file changes and then caused this. Am I wrong? Or is there a better way? Please let me know.

[rea1shane]

Also, what is the difference between template and includeTemplate? includeTemplate will be executed with data, while template will be executed without any data?

EDIT: I suddenly realized that template can also executed with context, and I'm even more confused about the difference between them. Should I always use includeTemplate instead of template?

[halostatue]

If you’re using homebrew for Linux, then it makes sense to do that. If not, then there's no value in the indirection, and you can make it so that Brewfile doesn't get generated on Linux by doing exactly what you’ve done, just incorporating the template in the one file.

[rea1shane]

If you’re using homebrew for Linux, then it makes sense to do that.

Yes, I will add the Linux part to the template later, but it doesn't yet, so it seems a little redundant.

[rea1shane]

template by itself should work in most cases, but there are cases when includeTemplate works and template doesn't

#4325 (reply in thread)

Also, what is the difference between template and includeTemplate? includeTemplate will be executed with data, while template will be executed without any data?

EDIT: I suddenly realized that template can also executed with context, and I'm even more confused about the difference between them. Should I always use includeTemplate instead of template?

Can anyone tell me the difference between the two? This would be very helpful for me to understand the template, thank you all very much.

[halostatue]

So, template is an action (built into Go's text/template language) and includeTemplate is a function (provided by chezmoi). In my experience, you can do {{ $foo := includeTemplate "foo" . }}, but you cannot do {{ $foo := template "foo" . }}.

$ chezmoi execute-template '{{ $foo := template "programs" . }}{{ $foo }}'
chezmoi: template: arg1:1: unexpected <template> in command
$ chezmoi execute-template '{{ $foo := includeTemplate "programs" . }}{{ $foo }}'
{"antiword":"antiword","bat":"bat","catdoc":"","catppt":"","delta":"delta","diff_so_fancy":"","difft":"difft","djvutxt":"","docx2txt_pl":"","exa":"","exiftool":"","eza":"eza","fzf":"fzf","gh":"gh","ghostty":"ghostty","git_absorb":"git-absorb","git_trim":"","gvim":"gvim","icdiff":"","in2csv":"","interactive_rebase_tool":"interactive-rebase-tool","ksdiff":"ksdiff","macos_open":"open","mvim":"mvim","odt2txt":"","open":"open","ov":"ov","pandoc":"pandoc","pdfinfo":"","pdftotext":"","pinentry_mac":"","pptx2md":"","soffice":"","ssh_chain":"","tika":"","unrtf":"","vim":"vim","wget":"wget","wvText":"","xdg_open":"","xlscat":"","xlsx2csv":"","xlsx2csv_py":"","ydiff":"ydiff","zoxide":"zoxide"}⏎

[rea1shane]

Ok, I understand a little bit, but I'm still not sure why includeTemplate works but template doesn't in this case. Anyway, thanks to each of you for your answers. I love the community atmosphere here.

[2-4601]

The difference between includeTemplate and template can be a bit confusing. Maybe it helps to see why it was introduced: #2314

Especially see comment:

This is possible because the builtin template is actually a control statement (like if and range). See https://github.com/golang/go/blob/master/src/text/template/parse/parse.go#L409-L410 for the implementation. text/template does not provide a method for users to add new control statements.

Just for illustrative purposes, if you try to replace template with if and range, you'll get a similar error:

$ chezmoi execute-template '{{ $foo := template "programs" . }}{{ $foo }}'
chezmoi: template: arg1:1: unexpected <template> in command

$ chezmoi execute-template '{{ $foo := if "programs" . }}{{ $foo }}'
chezmoi: template: arg1:1: unexpected <if> in command

$ chezmoi execute-template '{{ $foo := range "programs" . }}{{ $foo }}'
chezmoi: template: arg1:1: unexpected <range> in command

[rea1shane]

Hi @2-4601, thanks for your comment. I understand that the output of includeTemplate can be passed because of it is a func instead of control statement.

Now my biggest question is these two:

1. Should I use includeTemplate instead of template in various cases? includeTemplate looks more useful and can do all the things template can do.
2. What is the reason for the error in this comment? Why does there are cases when includeTemplate works and template doesn't? Is there a way to distinguish these cases?

It would be great if someone could answer these two questions.