YAML Processing with Shell Scripts

Introduction to YAML Processing

YAML (YAML Ain't Markup Language) is a human-readable data serialization standard that is commonly used for configuration files. This tutorial explores how to process YAML data using shell scripts.

Parsing YAML Files

Shell scripts can parse YAML files using tools like yq, which provides command-line YAML processing utilities.

Basic YAML Parsing

#!/bin/bash

# Parse and display YAML data from a file
FILE="config.yaml"

yq r "$FILE"
                

This script parses an YAML file and outputs its contents.

Extracting Specific Values

Extracting specific values from YAML files is a common task in YAML processing.

Extracting a Single Value

#!/bin/bash

# Extract a specific value from a YAML file
FILE="config.yaml"
KEY="database.host"

yq r -j "$FILE" | jq -r ".$KEY"
                

This script extracts and prints the value associated with the database.host key in a YAML file.

Extracting Multiple Values

#!/bin/bash

# Extract multiple values from a YAML file
FILE="config.yaml"
KEYS="database.host, database.port"

yq r -j "$FILE" | jq -r ". | {host: .database.host, port: .database.port}"
                

This script extracts and prints the values of the database.host and database.port keys from a YAML file.

Modifying YAML Data

Shell scripts can modify YAML data by updating existing values or adding new ones.

Updating Values

#!/bin/bash

# Update a value in a YAML file
FILE="config.yaml"
KEY="database.host"
NEW_VALUE="newhost.example.com"

yq w -i "$FILE" "$KEY" "$NEW_VALUE"
                

This script updates the value associated with the database.host key in a YAML file.

Adding New Values

#!/bin/bash

# Add a new value to a YAML file
FILE="config.yaml"
NEW_KEY="new.key"
NEW_VALUE="value"

yq w -i "$FILE" "$NEW_KEY" "$NEW_VALUE"
                

This script adds a new key-value pair to a YAML file.

Conclusion

YAML processing with shell scripts enables automation and manipulation of structured configuration data. By using tools like yq effectively, you can parse, extract, modify, and manipulate YAML data to suit your needs.