m3rger

m3rger is a tool for merging up to 3 layers of YAML configuration files.

Usage

$ ./m3rger-darwin --help
usage: m3rger-darwin [<flags>] <default> [<low>] [<high>]

Flags:
      --help     Show context-sensitive help (also try --help-long and --help-man).
  -o, --out=OUT  Write the output to a file (by default m3rger prints to stdout)
      --version  Show application version.

Args:
  <default>  A YAML file with default values that may be overridden
  [<low>]    A YAML file that will override any values in 'default', but not any in the 'high' file
  [<high>]   A YAML file whose keys will override anything from 'low' or 'default'

m3rger merges up to three files.

• default: A YAML file with default/generic values. If no other files are provided default is returned as is.
• low: Scalar values and arrays in this file will overwrite those of default whenever there is a collision. Maps are merged.
• high: Scalar values and arrays in this file will overwrite those of low and/or default whenever there is a collision. Maps are merged.

Docker usage

The only trick with running m3rger in a container is remembering that the files to be merged have to exist inside the container for m3rger to be able to read them. The easiest way to do that is using --volume to mount the directory the files are in:

$ ls
default.yml high.yml    low.yml
$ docker run --rm --read-only --volume=$(pwd):/input:ro \
    benjdewan/m3rger /input/default.yml /input/low.yml /input/high.yml
foo: mumble
key: val
map:
  baz: quux
  key: val

Examples

1. Just a default file

default.yml

foo: bar
map:
  key: val
  baz: qux

$ ./m3rger ./default.yml
foo: bar
map:
  key: val
  baz: qux

2. Two config files with no collision

default.yml

foo: bar
map:
  key: val
  baz: qux

override.yml

mumble: foobar

$ ./m3rger ./default.yml ./override.yml
foo: bar
map:
  key: val
  baz: qux
mumble: foobar

3. Two config files with a scalar collision

default.yml

foo: bar
map:
  key: val
  baz: qux

override.yml

foo: mumble

$ ./m3rger ./default.yml ./override.yml
foo: mumble
map:
  key: val
  baz: qux

4. Two conig files with a map merge

default.yml

foo: bar
map:
  key: val
  baz: qux

override.yml

map:
  key: mumble
  foo: bar

$ ./m3rger ./default.yml ./override.yml
foo: bar
map:
  key: mumble
  baz: qux
  foo: bar

5. Three way merge

default.yml

foo: bar
map:
  key: val
  baz: qux

low.yml

foo: baz
key: val
map:
  baz: zab

high.yml

foo: mumble
map:
  baz: quux

$ ./m3rger ./default.yml ./low.yml ./high.yml
foo: mumble
key: val
map:
  baz: quux
  key: val