Mastering jq: A Practical Guide to JSON Processing with Examples

sudo apt-get install jq

brew install jq

# Read from a file
jq '.' data.json

# Read from stdin
echo '{"name": "John", "age": 30}' | jq '.'

# Read from URL (with curl)
curl -s https://api.example.com/data | jq '.'

# Get specific field
jq '.name' data.json

# Get multiple fields
jq '.name, .age' data.json

# Get nested fields
jq '.user.profile.name' data.json

{
  "users": [
    {
      "id": 1,
      "name": "Alice",
      "email": "alice@example.com",
      "age": 28,
      "active": true
    },
    {
      "id": 2,
      "name": "Bob", 
      "email": "bob@example.com",
      "age": 35,
      "active": false
    },
    {
      "id": 3,
      "name": "Charlie",
      "email": "charlie@example.com",
      "age": 22,
      "active": true
    }
  ]
}

# Get all user names
jq '.users[].name' users.json

# Get active users only
jq '.users[] | select(.active == true)' users.json

# Get users over 25
jq '.users[] | select(.age > 25)' users.json

# Get names of active users
jq '.users[] | select(.active) | .name' users.json

# Count total users
jq '.users | length' users.json

# Get user emails as array
jq '[.users[].email]' users.json

{
  "total_count": 3,
  "items": [
    {
      "name": "repo1",
      "full_name": "user/repo1",
      "html_url": "https://github.com/user/repo1",
      "description": "First repository",
      "stargazers_count": 150,
      "language": "JavaScript"
    },
    {
      "name": "repo2",
      "full_name": "user/repo2", 
      "html_url": "https://github.com/user/repo2",
      "description": "Second repository",
      "stargazers_count": 89,
      "language": "Python"
    },
    {
      "name": "repo3",
      "full_name": "user/repo3",
      "html_url": "https://github.com/user/repo3",
      "description": "Third repository",
      "stargazers_count": 42,
      "language": "Go"
    }
  ]
}

# Get repository names and star counts
jq '.items[] | {name: .name, stars: .stargazers_count}' repos.json

# Get repositories with more than 100 stars
jq '.items[] | select(.stargazers_count > 100)' repos.json

# Get repository URLs
jq '.items[].html_url' repos.json

# Group by programming language
jq '.items | group_by(.language) | map({language: .[0].language, count: length})' repos.json

# Sort by star count (descending)
jq '.items | sort_by(.stargazers_count) | reverse' repos.json

# Create a summary
jq '{
  total_repos: .total_count,
  total_stars: (.items | map(.stargazers_count) | add),
  languages: (.items | map(.language) | unique)
}' repos.json

{
  "app": {
    "name": "MyApp",
    "version": "1.2.3",
    "settings": {
      "debug": true,
      "port": 8080,
      "database": {
        "host": "localhost",
        "port": 5432,
        "name": "myapp_db"
      }
    }
  },
  "features": {
    "auth": true,
    "logging": false,
    "cache": {
      "enabled": true,
      "ttl": 3600
    }
  }
}

# Get database configuration
jq '.app.settings.database' config.json

# Get all enabled features
jq '.features | to_entries | map(select(.value == true or (.value | type == "object" and .value.enabled == true)) | .key)' config.json

# Extract all port numbers
jq '.. | .port? | numbers' config.json

# Create simplified config
jq '{
  app_name: .app.name,
  version: .app.version,
  debug: .app.settings.debug,
  database: .app.settings.database.name
}' config.json

# Convert to uppercase
jq '.name | ascii_upcase' data.json

# String concatenation
jq '.first_name + " " + .last_name' data.json

# String interpolation
jq '"Name: \(.name), Age: \(.age)"' data.json

# Calculate average
jq '.numbers | add / length' data.json

# Find maximum value
jq '.numbers | max' data.json

# Sum specific fields
jq '[.users[].age] | add' users.json

# Conditional assignment
jq '.status = if .active then "active" else "inactive" end' user.json

# Multiple conditions
jq 'if .age < 18 then "minor" elif .age < 65 then "adult" else "senior" end' user.json

# Filter and map
jq '.users | map(select(.active) | {name: .name, email: .email})' users.json

# Unique values
jq '.languages | unique' data.json

# Array slicing
jq '.items[0:5]' data.json  # First 5 items
jq '.items[-5:]' data.json  # Last 5 items

# Extract error messages from logs
cat app.log | jq -r 'select(.level == "ERROR") | .message'

# Count errors by type
cat app.log | jq -r '.level' | sort | uniq -c

# Check API health status
curl -s https://api.status.example.com/health | jq '.status == "healthy"'

# Extract specific metrics
curl -s https://api.metrics.example.com/stats | jq '.response_time.p95, .error_rate'

# Compare two config files
diff <(jq -S . config1.json) <(jq -S . config2.json)

# Extract environment variables
jq -r 'to_entries | map("export \(.key)=\(.value|tostring)") | .[]' env.json