highlite

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highlite is a fast, rule-based CLI highlighter for stdin and files, written in Rust.

It reads text line by line and highlights matches using ANSI colors, making it suitable for large files, streaming input, and Unix-style pipelines.

Features

• High performance: all rules are compiled into a single regex at startup
• Rule-based highlighting using keywords or regular expressions
• Supports preset ANSI colors and 24-bit RGB colors
• YAML configuration with optional recursive includes
• Designed for streaming input (stdin, pipes, large files)
• Minimal memory allocation during processing
• Per-rule and global case-insensitive matching
• Built-in presets for common formats (logs, JSON...)
• Real-time log following:

  • --follow-journal to follow system logs

  • --follow-file <FILE> to follow a file like tail -f

Installation

From crates.io

cargo install highlite

From source

git clone https://github.com/sakimidare/highlite.git
cd highlite
cargo build --release

Usage

CLi Options:

Highlight stdin:

cat examples/logs/example_cpp.cpp | highlite --config examples/rules/cpp_rules.yaml

Highlight a file:

highlite --config examples/rules/log_rules.yaml --file examples/logs/example_log.log

Force case-insensitive matching for all rules:

highlite --config examples/rules/cpp_rules.yaml --ignore-case < examples/logs/example_cpp.cpp

Use a built-in preset

highlite --preset logs --file examples/logs/example_log.log

Follow system journal in real-time

highlite --preset logs --follow-journal

Follow a specific file in real-time (like tail -f)

highlite --preset cpp --follow-file examples/logs/example_cpp.cpp

NOTE: --follow-... has a higher priority than --file.

If stdin is a TTY, highlite will wait for input until EOF is received.

Built-in presets

Instead of providing a YAML configuration file, you can use one of the built-in presets:

• logs – common log highlighting
• cpp – C++ syntax highlighting
• json – JSON highlighting

Example:

highlite --preset cpp --file examples/logs/example_cpp.cpp

Configuration

The configuration file is written in YAML.

Basic structure

include:
  - common_optional.yaml

rules:
  - keyword: "TODO"
    color: { name: Yellow }
    ignore_case: true

  - keyword: "//.*|/\\*.*\\*/"
    is_regex: true
    ignore_case: false
    color: { r: 106, g: 153, b: 85 }

Rules

Each rule has the following fields:

• keyword The keyword or regular expression to match.

• is_regex (optional, default: false) Whether keyword should be treated as a regular expression.

• ignore_case (optional, default: false) Whether this rule should match text case-insensitively.

  Note: If the CLI flag --ignore-case is provided, all rules will be treated as case-insensitive, regardless of this setting.

• color The highlight color, either a preset name or an RGB value.

Colors

Preset colors

color: { name: Red }

color: { name: Yellow }

color: { name: Blue }

color: { name: Green }

color: { name: Cyan }

color: { name: Magenta }

RGB colors

color: { r: 106, g: 153, b: 85 }

Config Examples

See examples/logs for log highlighting examples. See examples/rules for YAML configuration examples.

Design

• All rules are merged into a single regular expression.

• Each rule corresponds to a named capture group.

• Case sensitivity is handled per rule using inline regex flags.

• Highlighting is performed in a single pass per line.

• Output buffers are reused to minimize allocations.

• This design keeps the implementation simple while maintaining high performance.

Limitations

• No nested highlighting (for example, comments inside strings).

• No cross-line strings or comments (for example: multiline /* */).

• No language-aware parsing; matching is purely regex-based.

• ANSI color output requires a compatible terminal.

License

This project is licensed under the GNU General Public License v3.0.

Contributing

Issues and pull requests are welcome.