Yamatter is a command-line tool to inspect and transform YAML front-matter data using js-yaml.

Installation

Install yamatter globally with npm:

npm install -g yamatter

Run yamatter without installing it with npx:

npx yamatter

Usage

yamatter [OPTIONS] [PATTERN ...]

Operands

The yamatter command accepts one or more glob patterns to match the files from which to read front-matter data.

The patterns are expanded by fast-glob. In order for the glob patterns to be expanded with fast-glob and not the shell that runs the command (e.g. sh, bash, zsh), make sure pass them enclosed in quotes:

yamatter 'content/**/*.md' 'notes/*.md'

yamatter looks for lines beginning with three or more hyphens (---) as the delimiter for front-matter data. Any matching files without front-matter data delimiters are ignored.

By default, yamatter ignores files matched by patterns inside .gitignore, if it finds one in the current working directory. It does not look for other .gitignore files neither up, nor down, the file system hierarchy. You can disable the ignore behavior with the --no-ignore flag.

Symbolic links (symlinks) are not followed. This helps avoid accidentally processing files outside the current working directory.

Options

--no-ignore

Don’t ignore files based on patterns found in .gitignore.

--silent

Don’t output to the standard output.

--no-filename

Don’t output filenames to the standard output.

--json

When outputting to the standard output, serialize the data as JSON instead of YAML.

-t <file>, --transform=<file>

Point to a JavaScript module, relative to the current working directory, that performs a transformation on the front-matter data.

The module must export a function that receives these arguments:

• data: a JSON object corresponding to the original front-matter data
• filepath: the source file path, relative to the current working directory

You can alter data directly, or return a new object in its place.

yamatter '*.md' -t to-uppercase.js

to-uppercase.js:

module.exports = function(data, filepath) {
	data.title = data.title.toUpperCase();
};

-w, --write

Write the result of the transformation back to the file.

Pro tip: Since this has the potential to be destructive, it is recommended that you run any yamatter --write commands in a folder that’s managed by a source control system such as Git, with any pending changes committed. This makes it easy to revert the files back to their original content.

--glob.<option>=<value>

Pass options to fast-glob directly. These options are passed by default:

{
	"followSymbolicLinks": false
}

Boolean and numeric values are cast to their respective data types. Other values are passed as strings, which limits the amount of fast-glob customization available.

--yaml.<option>=<value>

Pass serialization options to js-yaml’s dump() method. These options are passed by default:

{
	"lineWidth": -1
}

Boolean and numeric values are cast to their respective data types. Other values are passed as strings, which limits the amount of js-yaml customization available.

See also

• mikefarah/yq
• dbohdan/structured-text-tools