yq/pkg/yqlib/doc/operators/headers/multiply-merge.md

Multiply (Merge)

Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently numbers, arrays and objects are supported.

Objects and arrays - merging

Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.

Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.

Merge Flags

You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. .a *+? .b. See examples below

• + append arrays
• d deeply merge arrays
• ? only merge existing fields
• n only merge new fields
• c clobber custom tags

Merge two files together

This uses the load operator to merge file2 into file1.

yq '. *= load("file2.yml")' file1.yml

Merging all files

Note the use of eval-all to ensure all documents are loaded into memory.

yq eval-all '. as $item ireduce ({}; . * $item )' *.yml

Merging complex arrays together by a key field

By default - yq merge is naive. It merges maps when they match the key name, and arrays are merged either by appending them together, or merging the entries by their position in the array.

For more complex array merging (e.g. merging items that match on a certain key) please see the example here