Yaml files can be surprisingly lenient in what can be parsed as a yaml file. A reasonable way of validation a yaml file is to ensure the top level is a map or array (although it is valid yaml to have scalars at the top level, but often this is not what you want). This can be done by:
```
yq e --exit-status 'tag == "!!map" or tag== "!!seq"' file.txt > /dev/null
```
## Split expressions over multiple lines to improve readablity
Feel free to use multiple lines in your expression to improve readability.
```bash
yq eval --inplace '
.a.b.c[0].frog = "thingo" |
.a.b.c[0].frog style= "double" |
.different.path.somehere = "foo" |
.different.path.somehere style= "folded"
' my_file.yaml
```
## Create bash array
Given a yaml file like
```yaml
coolActions:
- create
- edit
- delete
```
You can create a bash array named `actions` by:
```bash
> readarray actions < <(yq e '.coolActions[]' sample.yaml)
The `strenv` operator is a great way to handle special characters in strings:
```bash
VAL='.a |!@ == "string2"' yq e '.a = strenv(VAL)' example.yaml
```
## Quotes in Windows Powershell
Powershell has its [own](https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about\_quoting\_rules?view=powershell-7.1) way of handling quotes:
To merge all given yaml files into one, use the `reduce` operator with the `*` (multiply) operator. Note the use of `ea` or `eval-all` to load all files into memory so that they can be merged.
```
yq ea '. as $item ireduce ({}; . * $item )' file1.yml file2.yml ...
```
## Creating a new file / working with blank documents
To create a new `yaml` file simply:
```
yq e -n '.someNew="content"' > newfile.yml
```
## Comparing yaml files
The best way to run a diff is to use `yq` to normalise the yaml files and then just use diff. Here is a simple example of using pretty print `-P` to normalise the styling and running diff:
```
diff <(yq e -P examples/data1.yaml) <(yq e -P examples/data2.yaml)
```
This way you can use the full power of `diff` and normalise the yaml files as you like - for instance you may also want to remove all comments using `... comments=""`
## Reading multiple streams (STDINs)
Like `diff` and other bash commands, you can use `<(exp)` to pipe in multiple streams of data into `yq`. instance:
```
yq e '.apple' <(curl -s https://somewhere/data1.yaml) <(cat file.yml)
```
## Updating deeply selected paths
The most important thing to remember to do is to have brackets around the LHS expression - otherwise what `yq` will do is first filter by the selection, and then, separately, update the filtered result and return that subset.
The first argument expression sets the root context, and the second expression runs against that root context.
## yq adds a !!merge tag automatically
The merge functionality from yaml v1.1 (e.g. `<<:`has actually been removed in the 1.2 spec. Thankfully, `yq` underlying yaml parser still supports that tag - and it's extra nice in that it explicitly puts the `!!merge` tag on key of the map entry. This tag tells other yaml parsers that this entry is a merge entry, as opposed to a regular string key that happens to have a value of `<<:`. This is backwards compatible with the 1.1 spec of yaml, it's simply an explicit way of specifying the type (for instance, you can use a `!!str` tag to enforce a particular value to be a string.
Although this does affect the readability of the yaml to humans, it still works and processes fine with various yaml processors.
