YAML for Linux

The package that I used to modify .yaml files was the most used and updated called yq that can be directly installed by that name with sudo apt install yq

Creating yaml files/keys

To create a yaml file you will have to do it the normal way with: touch <FILE>.yaml

In yaml’s data system, it follows the same structure as dictionaries where you can store different values with certain “keys” that can be used to call/modify those values.

To create a new key + value, you need to both input them into the file.

Note: You must include a value when declaring a key with yq

Lets start by making a data1 key with value 69 into a file called testing.yaml

yq -yi '.data1 = 69' testing.yaml #testing.yaml must be an existing file

Breakdown:
  • yq will call upon the yaml editing command
  • -yi will be used to WRITE to the file rather than READ
  • .data1 identifies the key in the dictionary that we are focusing on
  • = 69 sets the value of the data1 key to the integer 69
  • testing.yaml is the file that will be edited

Now lets make a dictionary inside a dictionary, its just as simple as the first step, but instead you insert it into the main dictionary name:

yq -yi '.mainDictionary.data1 = 69' testing.yaml

Now, you might be thinking “What if I don’t want to have a value assigned to the key?”, not possible friend, at least not with yq, instead you have to echo it into the file like so: Creating a new key called data2 with no value

echo "data2:" >> testing.yaml

This will create an empty key, if you were to read it, it would print: data2: null

Deleting yaml elements

To delete an element, you need the name of the key

yq -yi 'del(.mainDictionary.data1) testing.yaml

This will delete the data1 key and its value from inside the mainDictionary dictionary If you don’t include -yi it will just print out what it would be like IF the element was deleted

Using yq with variables

The way to include variables is very weird and follows a similar style to the sed command

When using variables you MUST use double brackets “, not single ‘

If you want to do just a variable-named key, do: yq -yi ".mainDictionary.$VariableName = 69" testing.yaml

For variable-named values, you must include an extra cover of double brackets: yq -yi '.mainDictionary.data1 = "$VariableName"' testing.yaml

For BOTH variable-named keys and values, its a bit more weird yq -yi ".mainDictionary.$KeyName = \"$ValueName\"" testing.yaml As you can see I used \" around the value instead of just ", that is because you NEED double brackets for variable, but you also need it to prevent the quotes from closing

Making comments:

Given a sample.yml file of:

a:
  # comment on key
  x: 3
  y: 4

You can use this command to print/add comments

yq '.a.x | key | headComment' sample.yml

will output the head comment of the key above it:

comment on key