Full examples of modifying part of a file with chezmoi

[jmlucjav]

Hi,

I am trying to use the 'modify_' approach here https://www.chezmoi.io/user-guide/manage-different-types-of-file/ to handle just part of a file. But I am not fully understanding what files I need to to do 'chezmoi add' for, the original file (let's call it x.rc) or the modify_x.rc, or both?

There is even an issue #1746 asking about an example, but it's not clear what file needs to be added either.

much appreciated!

[twpayne]

You need to create the modify_ script manually in your source directory. You can't use chezmoi add for this.

[jmlucjav]

thanks Tom, couple follow up questions...

• x.rc is 'chezmoi add'-ed as usual?
• so if I use chezmoi in 3 computers, I need to take care to keep the modify_ script in sync in the source dir manually, is that it?

[bradenhilton]

x.rc is 'chezmoi add'-ed as usual?

x.rc is the target file for both x.rc and modify_x.rc. You can't have multiple files in the source state referring to the same target.

x.rc's contents will be set to the output of the modify_ script, even if the output is empty. If you don't want x.rc to ever be empty, you need to ensure that the script outputs a sufficient minimal configuration.

so if I use chezmoi in 3 computers, I need to take care to keep the modify_ script in sync in the source dir manually, is that it?

modify_x.rc is the only file that is needed. If you need different contents on these machines then you need to use templating.

Here is a contrived example:

~/data.json:

{
  "color": "red"
}

<chezmoi source>/modify_data.json:

// chezmoi:modify-template

{{- $currentConfig := .chezmoi.stdin | fromJson -}}
{{- $modifiedConfig := .chezmoi.stdin | fromJson -}}

{{- $_ := set $modifiedConfig "color" "blue" -}}

{{- if deepEqual $currentConfig $modifiedConfig -}}
{{-   .chezmoi.stdin }}
{{- else -}}
{{-   $modifiedConfig | toPrettyJson }}
{{- end -}}

❯ chezmoi diff
diff --git a/data.json b/data.json
index 2f67018551056b7c2e17a2c6da5b7ecbe7a0a15c..c7f2e0cfc95110175c59e9579dae0fc1e3e92c0c 100666
--- a/data.json
+++ b/data.json
@@ -1,3 +1,3 @@
 {
-  "color": "red"
+  "color": "blue"
 }

[jmlucjav]

thanks for the explanation...bear with me, I must be missing something obvious cause still not working for me...

x.rc is 'chezmoi add'-ed as usual?

x.rc is the target file for both x.rc and modify_x.rc. You can't have multiple files in the source state referring to the same target.

ok got it, I created ~/.local/share/chezmoi/dot_config/modify_kdiff3rc:

#!/bin/bash

# copy the data to modify to a temporary file
tmpfile=$(mktemp)
trap "rm -f ${tmpfile}" EXIT
cat > "${tmpfile}"

#remove unwanted lines
sed -i '/shell-geometry/d' ${tmpfile}

# write the data to stdout
cat "${tmpfile}"

tested it invoking it and it does what I want (discard changes in line containing 'shell-geometry'). I push it without using 'chezmoi add'

chezmoi git add dot_config/modify_kdiff3rc && chezmoi git -- commit -m 'modify_kdiff3rc' && chezmoi git push

Made sure ~/.local/share/chezmoi/dot_config/kdiff3rc does not exist anymore.

But now, if I change a buch of lines in ~/.config/kdiff3rc (so I want those changes propagated to other host when I do chezmoi update), nothing happens, my changes stay just in this host.

Sorry about this, I'm quite obtuse when it comes to git and chezmoi feels like black magic sometimes

[bradenhilton]

When using a modify_ script, the contents of the file are no longer managed in the "traditional" way by chezmoi. Put simply, chezmoi just feeds the current contents of the file to the script via stdin, and uses its stdout to set the new contents of the file.

If you have changes you want to propagate, this would need to be done with the script itself, not the file.

You might want to explore using template functions such as fromIni, toIni, setValueAtPath, deleteValueAtPath etc. if you require something more robust than simple pattern replacements.

[jmlucjav]

When using a modify_ script, the contents of the file are no longer managed in the "traditional" way by chezmoi. Put simply, chezmoi just feeds the current contents of the file to the script via stdin, and uses its stdout to set the new contents of the file.

If you have changes you want to propagate, this would need to be done with the script itself, not the file.

oh ok...that is a big caveat that defeats the purpose of using modify_....

You might want to explore using template functions such as fromIni, toIni, setValueAtPath, deleteValueAtPath etc. if you require something more robust than simple pattern replacements.

I will look into those and see if I can get it working without modify_ thanks!

[bradenhilton]

that is a big caveat that defeats the purpose of using modify_....

I'm not sure I understand what you mean by this. Can you give a concrete example of what you want to achieve, and why you think a modify_ script isn't suitable?

[jmlucjav]

Take kdiff3rc for example, this is an .ini type file, and has maybe 100 entries. I am interested in synching this file over all my hosts, but there is one entry, 'shell-geometry' that is about the window size etc. Depending on my screen in each host this value changes every time, and I don't want this change to 'pollute' my git repo, I am not interested in propagating this value to other hosts, but I want all other changes.

I understood (maybe wrong) that I cannot achieve that with modify_ (getting changes from one host to the others)

[twpayne]

If you're modifying complex .ini files, check out chezmoi_modify_manager.

[jmlucjav]

Update:

In case this is useful for someone. I think I found I solution that works well for me. I wanted:

• the target file to be kept in chezmoi, propagating to all hosts (this was fundamental)
• ignore some lines from that file (like typical timestamp values etc).

I added a hook pre re-add:

[hooks.re-add.pre]
    command = ".../.chezmoiscripts/pre_add_hook_discard_lines.sh"

And in the sh I just use sed to remove the lines I want to discard (of course other modifications would be possible).

Maybe would be worth mentioning this option here https://www.chezmoi.io/user-guide/manage-different-types-of-file/#manage-part-but-not-all-of-a-file ?