rgc

Blazing fast command output colorizer written in Rust. Drop-in alternative to grc with bundled YAML configs for 100+ commands, automatic pipe detection, and zero runtime dependencies — everything in a single ~2.5 MB binary.

Disclaimer

This project was entirely written with the help of AI as a proof of concept. It is provided "as is", without warranty of any kind, express or implied. The author does not bear any responsibility and does not guarantee correctness, reliability, fitness for any particular purpose, or continued maintenance. Use at your own risk.

Quick Start

# colorize any supported command
rgc ping 8.8.8.8
rgc docker ps
rgc df -h

# pipe mode — auto-detects the command
mount | rgc
ps aux | rgc

# generate shell aliases so every command is colorized automatically
source <(rgc --aliases)

Installation

curl -sfL https://raw.githubusercontent.com/flameshikari/rgc/master/install.sh | sudo sh

Or build from source:

cargo build --release
sudo cp target/release/rgc /usr/local/bin/

To update an existing installation:

rgc --update

How It Works

rgc mount          # spawns mount in a PTY, colorizes stdout
mount | rgc        # detects "mount" via process group, colorizes stdin
rgc -c ping < file # uses explicit config

1. Config resolution — command name is matched against command: fields in YAML configs via O(1) HashMap lookup. Compound commands like docker ps and ip addr are matched with subcommand awareness
2. Pipe auto-detection — in pipe mode, rgc finds the writing process by scanning /proc for process group siblings. A pre-main .init_array hook captures the peer before Rust's runtime starts, catching even fast-exiting commands
3. PTY streaming — in direct mode, the child runs in a pseudo-terminal so it line-buffers its output. Real-time streaming for tcpdump, ping, tail -f, etc.
4. Dual regex engine — patterns are compiled with the regex crate (SIMD-accelerated, linear-time) first. Only patterns with lookbehind/lookahead fall back to fancy-regex
5. Wrapper stripping — rgc sudo tcpdump and sudo tcpdump | rgc both correctly resolve to the tcpdump config

Benchmarks

Measured with hyperfine. Linux 6.6 (WSL2), Intel i5-13600KF, Rust 1.94, grc 1.13. Mean of 10 runs, 2 warmup runs. "bare" = command without any colorizer.

Command execution (end-to-end wall-clock)

Command	bare	rgc	grc	rgc overhead	grc overhead	Speed difference
env	0.4 ms	1.4 ms	34.5 ms	+1.0 ms	+34.1 ms	24x
mount	0.7 ms	2.1 ms	33.2 ms	+1.4 ms	+32.5 ms	16x
lsmod	0.9 ms	1.9 ms	34.2 ms	+1.0 ms	+33.3 ms	18x
ip addr	1.1 ms	3.3 ms	34.0 ms	+2.2 ms	+32.9 ms	10x
lsblk	1.5 ms	4.1 ms	35.3 ms	+2.6 ms	+33.8 ms	8x
df -h	1.4 ms	4.7 ms	34.0 ms	+3.3 ms	+32.6 ms	7x
netstat -tln	2.3 ms	6.0 ms	32.9 ms	+3.7 ms	+30.6 ms	5x
ps aux	2.3 ms	10.4 ms	35.4 ms	+8.1 ms	+33.1 ms	3x
docker network ls	10.5 ms	12.4 ms	34.7 ms	+1.9 ms	+24.2 ms	3x
docker ps	10.2 ms	14.2 ms	36.0 ms	+4.0 ms	+25.8 ms	2.5x

Throughput (1M lines piped through colorizer)

Config	rgc	grc	Speed difference
log (5 rules)	0.55 s	4.46 s	8x
ps (17 rules)	2.45 s	7.98 s	3x

Streaming (I/O-bound, wall-clock includes network wait)

Command	bare	rgc	grc
ping -c 3 127.0.0.1	2.002 s	2.025 s	2.043 s

rgc vs grc

	rgc	grc
Binary	Single ~2.5 MB binary, all configs bundled	Python runtime + config files in /usr/share/grc/
Startup	~2 ms	~33 ms
Config format	YAML with palette, named groups, when filtering	Custom INI-like with ====== separators
Regex	SIMD-accelerated regex + fancy-regex fallback	Python re
Colors	Standard 16, 256-color, RGB	Standard 16 only
Streaming	PTY-based, always line-buffered	--pty flag (experimental)
Pipe detection	Auto-detects via process group	Requires separate grcat binary + explicit config
Config source	command: field in each YAML config	Separate grc.conf mapping file
External configs	-d <path> with auto-discovery	~/.grc/ directory

Supported Commands

Run rgc --list to see all supported commands. Config files are in the configs/ directory — each YAML file defines which commands it handles and the colorization rules for them.

Syntax highlighters without a bound command (use with -c): common, log, sql, yaml, php, jobs.

Config Format

Configs use YAML with the following structure:

command:
  - ping
  - ping6

palette:
  ip: bright_blue

rules:
  - name: IP address
    pattern: '\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}'
    colors: [ip]

  - name: icmp_seq
    pattern: 'icmp_seq=(\d+)'
    colors: [default, yellow]
    count: more

Fields

Field	Description
command	List of commands this config applies to. Supports subcommands (docker ps, ip addr)
palette	Reusable color aliases resolved at parse time
rules[].pattern	Regex pattern. Supports lookahead/lookbehind via fancy-regex fallback
rules[].colors	Positional list or named map (for (?P<name>...) groups)
rules[].name	Optional rule description
rules[].when	Scope rule to specific commands in merged configs
rules[].count	more (default), once, stop, previous, block, unblock
rules[].skip	Skip the line entirely if matched
rules[].replace	Replacement string (supports $1, $2 backreferences)

Colors

Standard: red, green, yellow, blue, magenta, cyan, white, black and bright_* variants. Prefixed with on_ for background. Modifiers: bold, underline, italic, dim, blink, reverse, hidden. Special: default (no change for group 0), unchanged, previous.

Extended: color256(N), on_color256(N), rgb(R,G,B), on_rgb(R,G,B).

Named Capture Groups

- pattern: '(?P<key>\w+)=(?P<val>.+)'
  colors:
    key: bold cyan
    val: green

Merged Configs with when

command:
  - docker ps
  - docker images

rules:
  - pattern: HEADERS
    colors: [underline]
    when: [docker ps]

Use -d <path> to load configs from a directory instead of bundled ones.

Environment Variables

Variable	Effect
NO_COLOR	Disable all colorization (output passes through unmodified)
FORCE_COLOR	Force colorization even when stdout is not a TTY

Limitations

• Linux only (uses /proc, PTY, .init_array)
• Pipe auto-detection relies on process group scanning — ultra-fast commands like env may exit before detection. Use direct mode (rgc env) or -c for these
• In pipe mode, upstream buffering is controlled by the sender, not rgc. Use direct mode for real-time streaming

License

Config files are based on grc by Radovan Garabik (GPL-2.0). The rest of the code is GPL-2.0 too.