Merging yaml config files recursively with bash

No.

Bash has no support for nested data structures (its maps are integer->string or string->string only), and thus cannot represent arbitrary YAML documents in-memory.

Use a more powerful language for this task.

Late to the party, but I also wrote a tool for this:

https://github.com/benprofessionaledition/yamlmerge

It's almost identical to Ondra's JVM tool (they're even both called "yaml merge"), the key difference being that it's written in Go so it compiles to a ~3MB binary with no external dependencies. We use it in Gitlab-CI containers.

I recommend yq -m. yq is a swiss army knife for yaml, very similar to jq (for JSON).

You can use for example perl. The next oneliner:

perl -MYAML::Merge::Simple=merge_files -MYAML -E 'say Dump merge_files(@ARGV)' f1.yaml f2.yaml

for the next input files: f1.yaml

date:
  epoch: 2342342343
  format:
    date_regular: "%d-%m-%Y"

f2.yaml

date:
  format:
    date_regular: regular dates are boring
    date_special: "!!!%d-%m-%Y!!!"

prints the merged result...

---
date:
  epoch: 2342342343
  format:
    date_regular: regular dates are boring
    date_special: '!!!%d-%m-%Y!!!'

Because @Caleb pointed out that the module now is develeloper only, here is an replacement. It is a bit longer and uses two (but commonly available) modules:

• the YAML
• and the Hash::Merge::Simple

perl -MYAML=LoadFile,Dump -MHash::Merge::Simple=merge -E 'say Dump(merge(map{LoadFile($_)}@ARGV))' f1.yaml f2.yaml

produces the same as above.