1). STORE YOUR VAULT PASSWORD IN A FILE
```
echo "<SOME_PASSWORD>" > ~/.vault_pass.txt
```

2). ENCRYPTING A FILE:

Before encrypting ...
```
$ cat group_vars/all
ansible_ssh_user: root
ansible_ssh_password: <SOME_PASSWORD>
```

Encrypt ...
```
$ ansible-vault encrypt group_vars/all
[You will be prompted for vault password]
```

Look at the results ...
```
$ cat group_vars/all
$ANSIBLE_VAULT;1.1;AES256
32636530636135626164616334623564623132663139636436646163663035346239663232666233
6666633735653535666132306533653061323262656338320a333566356433326563636537386564
66396337616333646565333566356632646530623536636166316639363135373364646130643230
3937346363356165380a353665646138316663653237376238333038303637336430336333616139
36303165353138366232333430643362356531343030366363613264303137366662343533303766
65363234343337326234346335303035613439363934633765323964323865373334653836613434
61373832623935353866363934623866303837343164386565306533306334376163313364363839
33373435643565323865653963653839656361646162333434333136383563636631386465376666
62643062613863343165393033376637393332356266396134353035396264313861
```

3). TO DECRYPT A FILE:

Decrypt ...
```
ansible-vault decrypt group_vars/all
[You will be prompted for vault password]
```

Look at the results ...
```
$ cat group_vars/all
ansible_ssh_user: root
ansible_ssh_password: <SOME_PASSWORD>
```

4). PROVIDE VAULT PASSWORD IN PLAYBOOK RUN TO USE ENCRYPTED VAR FILE
```
ansible-playbook -i hosts -u someuser --vault-password-file ~/.vault_pass.txt
```