logtail

logtail v0.1.0 (Beta)

Initial beta release of logtail — a high-performance CLI tool for streaming and filtering large log files.

Why logtail?

Because existing tools fall apart when logs get big or workflows get real.

• tail -f → no filtering
• grep → not built for real-time streaming
• heavy log tools → overkill for simple debugging

logtail focuses on doing one thing well:

Stream large files, filter them in real time, and stay fast with minimal memory usage.

Features

• Stream large files without loading them into memory
• Follow file updates (--follow, like tail -f)
• Filter using substring or regular expressions
• Case-insensitive matching
• Invert match
• Line numbers
• Count matches
• Works with files and stdin

---

Installation

Build from source

git clone https://github.com/YOUR_USERNAME/logtail.git
cd logtail
cargo build --release

Usage

Basic usage

logtail [FILE]

Follow file (like tail -f)

logtail [FILE] --follow

or

logtail [FILE] -f

Filter by substring

logtail [FILE] --contains "ERROR"

or

logtail [FILE] -c "ERROR"

Filter by regex

logtail [FILE] --regex "ERROR|WARN"

or

logtail [FILE] -r "ERROR|WARN"

Case-insensitive matching

logtail [FILE] -r "error" -i

Invert match (exclude lines)

logtail [FILE] -c "DEBUG" -v

Show line numbers

logtail [FILE] -n

Count matches only

logtail [FILE] -c "ERROR" -C

Pipe input (stdin)

cat [FILE] | logtail -c "ERROR"

Examples

Monitor errors in real time

logtail /var/log/app.log -f -r "ERROR|PANIC"

Exclude noisy logs

logtail /var/log/app.log -v -c "DEBUG"

Count failed requests

logtail /var/log/app.log -r "status=500" --count

Debug logs with line numbers

logtail /var/log/app.log -c "DEBUG" -n

Performance

logtail is designed with performance in mind:

• Uses streaming I/O (BufReader)
• Processes logs line-by-line
• Avoids loading full files into memory
• Reuses buffers to reduce allocations
• Compiles regex once

Memory usage is independent of file size.

Limitations (Beta)

• Basic file rotation handling
• Case-insensitive substring matching allocates per line (to be optimized)
• No multi-file support yet
• No structured log parsing (JSON, etc.)

Roadmap

• Improved file rotation detection (inode tracking)
• Faster case-insensitive matching
• Multi-file support
• JSON log filtering
• Highlighting matches
• Performance benchmarks

License

MIT License