yq/pkg/yqlib/doc/Multiply.md

Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.

To concatenate arrays when merging objects, use the *+ form (see examples below). This will recursively merge objects, appending arrays when it encounters them.

To merge only existing fields, use the *? form. Note that this can be used with the concatenate arrays too *+?.
Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.

Multiplication of strings and numbers are not yet supported.

## Merging files
Note the use of `eval-all` to ensure all documents are loaded into memory.

```bash
yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
```

## Merge objects together, returning merged result only
Given a sample.yml file of:
```yaml
a:
  field: me
  fieldA: cat
b:
  field:
    g: wizz
  fieldB: dog
```
then
```bash
yq eval '.a * .b' sample.yml
```
will output
```yaml
field:
  g: wizz
fieldA: cat
fieldB: dog
```

## Merge objects together, returning parent object
Given a sample.yml file of:
```yaml
a:
  field: me
  fieldA: cat
b:
  field:
    g: wizz
  fieldB: dog
```
then
```bash
yq eval '. * {"a":.b}' sample.yml
```
will output
```yaml
a:
  field:
    g: wizz
  fieldA: cat
  fieldB: dog
b:
  field:
    g: wizz
  fieldB: dog
```

## Merge keeps style of LHS
Given a sample.yml file of:
```yaml
a: {things: great}
b:
  also: "me"

```
then
```bash
yq eval '. * {"a":.b}' sample.yml
```
will output
```yaml
a: {things: great, also: "me"}
b:
  also: "me"
```

## Merge arrays
Given a sample.yml file of:
```yaml
a:
  - 1
  - 2
  - 3
b:
  - 3
  - 4
  - 5
```
then
```bash
yq eval '. * {"a":.b}' sample.yml
```
will output
```yaml
a:
  - 3
  - 4
  - 5
b:
  - 3
  - 4
  - 5
```

## Merge, only existing fields
Given a sample.yml file of:
```yaml
a:
  thing: one
  cat: frog
b:
  missing: two
  thing: two
```
then
```bash
yq eval '.a *? .b' sample.yml
```
will output
```yaml
thing: two
cat: frog
```

## Merge, appending arrays
Given a sample.yml file of:
```yaml
a:
  array:
    - 1
    - 2
    - animal: dog
  value: coconut
b:
  array:
    - 3
    - 4
    - animal: cat
  value: banana
```
then
```bash
yq eval '.a *+ .b' sample.yml
```
will output
```yaml
array:
  - 1
  - 2
  - animal: dog
  - 3
  - 4
  - animal: cat
value: banana
```

## Merge, only existing fields, appending arrays
Given a sample.yml file of:
```yaml
a:
  thing:
    - 1
    - 2
b:
  thing:
    - 3
    - 4
  another:
    - 1
```
then
```bash
yq eval '.a *?+ .b' sample.yml
```
will output
```yaml
thing:
  - 1
  - 2
  - 3
  - 4
```

## Merge to prefix an element
Given a sample.yml file of:
```yaml
a: cat
b: dog
```
then
```bash
yq eval '. * {"a": {"c": .a}}' sample.yml
```
will output
```yaml
a:
  c: cat
b: dog
```

## Merge with simple aliases
Given a sample.yml file of:
```yaml
a: &cat
  c: frog
b:
  f: *cat
c:
  g: thongs
```
then
```bash
yq eval '.c * .b' sample.yml
```
will output
```yaml
g: thongs
f: *cat
```

## Merge copies anchor names
Given a sample.yml file of:
```yaml
a:
  c: &cat frog
b:
  f: *cat
c:
  g: thongs
```
then
```bash
yq eval '.c * .a' sample.yml
```
will output
```yaml
g: thongs
c: &cat frog
```

## Merge with merge anchors
Given a sample.yml file of:
```yaml
foo: &foo
  a: foo_a
  thing: foo_thing
  c: foo_c
bar: &bar
  b: bar_b
  thing: bar_thing
  c: bar_c
foobarList:
  b: foobarList_b
  !!merge <<:
    - *foo
    - *bar
  c: foobarList_c
foobar:
  c: foobar_c
  !!merge <<: *foo
  thing: foobar_thing
```
then
```bash
yq eval '.foobar * .foobarList' sample.yml
```
will output
```yaml
c: foobarList_c
<<:
  - *foo
  - *bar
thing: foobar_thing
b: foobarList_b
```