rcat — render Markdown (and 60+ source/config formats) in the terminal

rcat is a small, fast C++17 CLI that renders Markdown files inline in your terminal — with ANSI styling, OSC 8 hyperlinks, Unicode box-drawing, syntax-highlighted code fences, and optional inline image rendering via chafa. When the input isn't Markdown, rcat falls back to a built-in syntax highlighter that knows ~60 languages and config formats, so it works as a drop-in cat replacement that also pretty-prints whatever you throw at it.

A companion binary, rless, takes the same rendered output and runs it through an interactive less-style pager — scroll, page, jump to top/bottom, and search through Markdown or source files the same way you would less a log file.

rcat README.md
rcat src/rcat.cpp
curl -fsSL https://example.com/post.md | rcat -

rless README.md          # interactive pager
rless src/rcat.cpp       # same, with syntax highlighting

Features

• CommonMark + GFM-ish Markdown via md4c: headings, lists, blockquotes, tables, task lists, autolinks, strikethrough.
• Syntax highlighting for ~60 languages — C/C++, Rust, Go, Python, Ruby, Perl, Shell, PowerShell, SQL, Lua, Haskell, OCaml, Erlang, Lisps, JSON/YAML/TOML/INI, HTML/XML/CSS, Dockerfile, Makefile, CMake, diff/patch, and more. Run rcat --lang list for the full set.
• Inline images (PNG/JPG/GIF/BMP/PSD/TGA/PNM) rendered as Unicode half-block art via chafa; works over SSH, tmux, and any colour terminal.
• Remote images with explicit opt-in (--allow-web, requires libcurl). Off by default; size- and time-capped.
• Terminal-aware: autodetects truecolour / 256 / 16 / mono, OSC 8 hyperlinks, UTF-8 vs ASCII, terminal width, and NO_COLOR.
• Internationalised via gettext (zh_CN, es, ja, de bundled).
• No GC, no runtime, one binary — ~200 KB stripped, links only what it needs.

Install

From source

Build requirements:

Component	Notes
C++17 compiler	gcc ≥ 8, clang ≥ 7, AppleClang ≥ 11
CMake	≥ 3.14
md4c	required
argparse	required (header-only, find via CMake)
libintl / gettext	required (translated messages + .mo compilation)
chafa + stb_image.h	required (inline image rendering)
libcurl	required (--allow-web remote image fetch)

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
sudo cmake --install build           # installs to /usr/local by default

To skip the test suite or man-page install:

cmake -S . -B build \
    -DRCAT_BUILD_TESTS=OFF \
    -DRCAT_INSTALL_MAN=OFF

Distribution packages

cmake --build build --target package produces .tar.gz, .deb, and .rpm archives via CPack when the host has the matching tooling.

Usage

rcat [OPTIONS] [FILE...]

Reads from stdin if no FILE is given (or FILE is -). Image paths in Markdown are resolved relative to each input file's directory.

Common flags (rcat --help for the full list, in your locale):

Flag	Effect
-c, --columns N	wrap to N columns (default: terminal width)
-p, --plain	strip styling entirely (just wrapped text)
--no-color	disable colour (keep Unicode/structure)
--force-color	emit colours even when stdout isn't a TTY
--ascii	ASCII-only output (no box-drawing/bullets)
--color MODE	auto, none, 16, 256, truecolor
--no-images	skip inline images even when chafa is built in
--allow-web	download http(s) image URLs (off by default)
--web-timeout S	per-image fetch timeout (default 10s)
--image-height N	max rendered image height in rows (default 20)
--no-hyperlinks	disable OSC 8 even when terminal supports it
--lang LANG	force language; md for Markdown, list to print all
-V, --version	print version

Environment

Variable	Effect
NO_COLOR	disable colour entirely (any value)
COLUMNS	override terminal-width autodetect
LANG, LC_*	drive locale + UTF-8 detection
RCAT_LOCALEDIR	where to look for .mo catalogs (defaults to install prefix)

Exit codes

Code	Meaning
0	success
1	one or more inputs failed to read or parse
2	bad command-line usage

Examples

Pipe through less while keeping colour:

rcat --force-color README.md | less -R

Pretty-print any source file cat-style:

rcat src/rcat.cpp
rcat /etc/hosts
rcat Dockerfile

Force a specific language for a file with an unusual extension:

rcat --lang yaml config.txt

rless — the pager

rless shares everything above (renderer, highlighter, terminal-cap detection, i18n) and adds an interactive viewport with less-style key bindings:

Key	Action
j, Down	down one line
k, Up	up one line
Space, f, PageDn	down one page
b, PageUp	up one page
d / u	down / up half a page
g, Home	top of buffer
G, End	bottom of buffer
/pattern	search forward (ASCII-icase)
?pattern	search backward
n / N	next / previous match
h, H	in-pager help
q, Q, Ctrl-C	quit

When stdout isn't a terminal — rless foo.md | grep bar, redirection to a file, etc. — or when --no-pager is given, rless skips the viewport and writes the rendered output, so it composes with pipelines like rcat does. Terminal resizes are handled by re-wrapping the buffer to the new width.

rless README.md                       # interactive
rless --no-pager src/rcat.cpp         # behave like rcat
rless --force-color README.md | aha   # ANSI → HTML

rless accepts the same renderer flags as rcat (--color, --columns, --no-images, --allow-web, --ascii, --lang, …). See rless --help or man rless for the full list.

Development

cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build -j
ctest --test-dir build --output-on-failure

Optional sanitizer builds:

cmake -S . -B build-asan -DCMAKE_BUILD_TYPE=Debug -DRCAT_ENABLE_ASAN=ON
cmake --build build-asan -j && ctest --test-dir build-asan

See CONTRIBUTING.md for the contribution flow, code style, and translation instructions.

License

Released under the GNU General Public License v3.0 or later. SPDX-License-Identifier: GPL-3.0-or-later.