LogFilter

A VS Code extension for pipeline-based log filtering. Write .lf rule files to filter, extract, and deduplicate log file content, then preview results directly in VS Code.

Features

• Pipeline filtering: Each rule's output feeds into the next, enabling progressive refinement
• Regex filtering: Keep lines matching a regex, or extract capture groups
• Deduplication: Remove duplicate lines globally or consecutively
• Preview panel: View filtered results in a dedicated webview panel
• Step-by-step execution: Click ▶ Filter (Ctrl+Enter) on any rule to run from the start up to that rule
• Quick execution: Press Ctrl+Enter on any line to run the nearest valid rule above the cursor
• Syntax highlighting: .lf files have full syntax highlighting and comment toggling (Ctrl+/)

Quick Start

Step 1: Create a .lf file

Open any .log file and click the CreateLogFilter button in the editor title bar. This creates a .lf file with the same name in the same directory.

Step 2: Write filter rules

Edit the .lf file with rules:

# Lines starting with # are comments

# Plain regex — keeps matching lines
ERROR

# Capture groups — extracts only captured content
\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]

# Commands starting with !
!dedupe

Step 3: Preview results

Go back to the .log file and click OpenPreview in the editor title bar. For step-by-step execution, click ▶ Filter (Ctrl+Enter) on any line in the .lf file, or press Ctrl+Enter with the cursor on that line.

Rule Syntax

Comments

# This is a comment (line must start with `#` followed by a space)

Regex patterns

Each line is a JavaScript regex applied to every line of the current set:

# Keep lines containing ERROR (plain filter)
ERROR

# Extract IP addresses (capture group extraction)
\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]

# Global flag g — multiple matches per line
(\w+)

Commands

Lines starting with ! operate on the entire current line set:

ERROR
\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]
!dedupe

Pipeline Mechanism

Each rule's output serves as the input for the next rule:

Raw log → Rule 1 → Result 1 → Rule 2 → Result 2 → ... → Preview

Example execution:

Raw log:
  ERROR [192.168.1.1] timeout
  INFO [10.0.0.5] heartbeat
  ERROR [192.168.1.1] retry

Rule 1: ERROR
  → Keeps lines with ERROR (2 lines)

Rule 2: \[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]
  → Extracts IP addresses (2 lines: 192.168.1.1 / 192.168.1.1)

Rule 3: !dedupe
  → Deduplicates (1 line: 192.168.1.1)

Editor Features

.log file operations

• CreateLogFilter: Creates a .lf file (button in editor title bar)
• OpenPreview: Applies all rules from the .lf file and shows preview

.lf file operations

• ▶ Filter (Ctrl+Enter): CodeLens button above each rule, runs from rule 1 to that line
• Ctrl+Enter: Run the nearest valid rule above the cursor (skips comments and blank lines)
• Syntax highlighting: Comments (green), commands (purple), regex (default)
• Ctrl+/: Toggle line comment

Installation

Install from VS Code Marketplace or build locally.

Note: The extension includes an icon (icons/icon-128.png) displayed on the Marketplace and in VS Code's extension list.

npm install
npm run compile

Press F5 in VS Code to launch an Extension Development Host for testing.

Examples

Example 1: Extract error IPs

app.log:

2024-01-15 ERROR [10.0.0.1] Connection refused
2024-01-15 INFO [10.0.0.2] Health check OK
2024-01-15 ERROR [10.0.0.1] Retry failed

app.lf:

ERROR
\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]
!dedupe

Preview result:

10.0.0.1

Example 2: Extract timestamps

(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2})

Example 3: Multiple capture groups

(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})[^\[]+\[(\w+)\]

Input 192.168.1.1 - admin [ERROR] produces:

192.168.1.1
ERROR

License

MIT