yq/mkdocs/write.md

```
yaml w <yaml file> <path> <new value>
```

### To Stdout
Given a sample.yaml file of:
```yaml
b:
  c: 2
```
then
```bash
yaml w sample.yaml b.c cat
```
will output:
```yaml
b:
  c: cat
```

### From STDIN
```bash
cat sample.yaml | yaml w - b.c blah
```

### Adding new fields
Any missing fields in the path will be created on the fly.

Given a sample.yaml file of:
```yaml
b:
  c: 2
```
then
```bash
yaml w sample.yaml b.d[0] "new thing"
```
will output:
```yaml
b:
  c: cat
  d:
    - new thing
```

### Updating files in-place
Given a sample.yaml file of:
```yaml
b:
  c: 2
```
then
```bash
yaml w -i sample.yaml b.c cat
```
will update the sample.yaml file so that the value of 'c' is cat.


### Updating multiple values with a script
Given a sample.yaml file of:
```yaml
b:
  c: 2
  e:
    - name: Billy Bob
```
and a script update_instructions.yaml of:
```yaml
b.c: 3
b.e[0].name: Howdy Partner
```
then

```bash
yaml w -s update_instructions.yaml sample.yaml
```
will output:
```yaml
b:
  c: 3
  e:
    - name: Howdy Partner
```

And, of course, you can pipe the instructions in using '-':
```bash
cat update_instructions.yaml | yaml w -s - sample.yaml
```