Data processing

Data Processing

Query, filter, and transform structured data (JSON, YAML, TOML) efficiently from the command line.

Tools

Tool	Command	Use For
jq	jq '.key' file.json	JSON processing
yq	yq '.key' file.yaml	YAML/TOML processing

jq Essentials

# Extract single field
jq '.name' package.json

# Extract nested field
jq '.scripts.build' package.json

# Extract from array
jq '.dependencies[0]' package.json

# Extract multiple fields
jq '{name, version}' package.json

# Navigate deeply nested
jq '.data.users[0].profile.email' response.json

# Filter by condition
jq '.users[] | select(.active == true)' data.json

# Transform each element
jq '.users | map({id, name})' data.json

# Count elements
jq '.users | length' data.json

# Raw string output
jq -r '.name' package.json

yq Essentials

# Extract field
yq '.name' config.yaml

# Extract nested
yq '.services.web.image' docker-compose.yml

# List all keys
yq 'keys' config.yaml

# List all service names (Docker Compose)
yq '.services | keys' docker-compose.yml

# Get container images (K8s)
yq '.spec.template.spec.containers[].image' deployment.yaml

# Update value (in-place)
yq -i '.version = "2.0.0"' config.yaml

# TOML to JSON
yq -p toml -o json '.' config.toml

Quick Reference

Task	jq	yq
Get field	jq '.key'	yq '.key'
Array element	jq '.[0]'	yq '.[0]'
Filter array	jq '.[] | select(.x)'	yq '.[] | select(.x)'
Transform	jq 'map(.x)'	yq 'map(.x)'
Count	jq 'length'	yq 'length'
Keys	jq 'keys'	yq 'keys'
Pretty print	jq '.'	yq '.'
Compact	jq -c	yq -o json -I0
Raw output	jq -r	yq -r
In-place edit	-	yq -i

When to Use

• Reading package.json dependencies
• Parsing Docker Compose configurations
• Analyzing Kubernetes manifests
• Processing GitHub Actions workflows
• Extracting data from API responses
• Filtering large JSON datasets
• Config file manipulation
• Data format conversion

Additional Resources

For complete pattern libraries, load:

• ./references/jq-patterns.md - Arrays, filtering, transformation, aggregation, output formatting
• ./references/yq-patterns.md - Docker Compose, K8s, GitHub Actions, TOML, YAML modification
• ./references/config-files.md - package.json, tsconfig, eslint/prettier patterns