cli-output-filter

A CLI tool for filtering repetitive output from commands while preserving important information and providing statistics on what was filtered.

Installation

npm install -g cli-output-filter

Usage

Basic Usage

# Filter output from any command
filter-output --patterns patterns.json <command> [args...]

# Example: Filter CDK synth output
filter-output --patterns patterns.json cdk synth

# Example: Filter build output
filter-output --patterns patterns.json npm run build

Pattern File Format

Create a JSON file with filter patterns:

[
  {
    "name": "debug-messages",
    "pattern": "^DEBUG:",
    "streams": ["stdout", "stderr"]
  },
  {
    "name": "info-messages",
    "pattern": "^INFO:",
    "streams": ["stdout"]
  }
]

Fields:

• name - Identifier for the pattern (used in statistics)
• pattern - Regular expression to match lines
• streams - Array of streams to filter: ["stdout"], ["stderr"], or ["stdout", "stderr"]

Output

The tool shows filtered command output in real-time and provides a summary at the end:

=== Filter Summary ===
Total Lines: 1000
Filtered Out: 850
Lines Shown: 150
Filtered Out Percentage: 85%

Pattern: "debug-messages" (from stdout)
  Lines Filtered Out: 500 (50%)
  Example: DEBUG: Initializing component...

Pattern: "info-messages" (from stdout)
  Lines Filtered Out: 350 (35%)
  Example: INFO: Processing request...

Use Cases

• Build Output: Remove verbose logging while keeping errors
• Test Output: Hide passing test details, show only failures
• CI/CD Logs: Reduce log volume while preserving important information
• Development: Filter repetitive warnings and deprecation notices

Features

• ✅ Real-time filtering (no buffering)
• ✅ Preserves command exit codes
• ✅ Handles both stdout and stderr
• ✅ Provides detailed statistics
• ✅ Shows example of each filtered pattern
• ✅ Regex pattern matching
• ✅ Signal forwarding (SIGINT, SIGTERM, SIGQUIT)

Requirements

• Node.js >= 20

License

MIT