Install unifdef with Homebrew, apk, apt, dnf, MacPorts, Nix, pacman, zypper

Project links

• Homepage
• Repository

Commands and aliases

• unifdef
• unifdefall

Project history

unifdef is much older than its GitHub mirror. The official manual states that the command appeared in 2.9BSD, and that ANSI C support was added in FreeBSD 4.7. It also credits the original implementation to Dave Yost and Tony Finch's rewrite for ANSI C support.

Tony Finch's official project page explains the modern motivation: understanding `xterm`'s heavily conditionalized pty-handling code. That places unifdef in the Unix source-reading and source-cleanup tradition rather than in general-purpose preprocessing.

The current project page publishes release archives, manual documentation, a browsable source repository, and a GitHub collaboration mirror. The GitHub README warns that GitHub release downloads are incomplete and points users back to the official dotat.at release files, which is useful context for packagers.

Adoption history

The official homepage gives a concrete high-profile adoption example: the Linux kernel uses unifdef to strip `#ifdef __KERNEL__` sections from headers exported to userland. It also notes use outside C, including LaTeX workflows.

The supplied package facts show broad distribution packaging across Homebrew, Debian/Ubuntu, Fedora/DNF, Alpine, Arch, MacPorts, Nix, openSUSE, and others. That matches the tool's age and purpose: it is small, portable, and useful in build and source-export pipelines.

How it is used

unifdef is used by specifying macros with `-D`, `-U`, or a definitions file, then filtering input files so known conditional branches are removed while unknown conditionals are preserved. It can operate on stdin/stdout or modify files in place.

The manual also documents `unifdefall`, a script that uses `unifdef -s` and `cpp -dM` to derive macro information and remove all conditional directives from a file. This shows the tool's role as a controlled partial preprocessor rather than a full C preprocessor replacement.

Why package nerds care

unifdef is important in the package-nerd niche because it is both tiny and historically deep: a BSD-era tool still used for practical source filtering. It belongs in base-system and package-manager collections because build scripts and source-export tasks can depend on it without pulling in a large toolchain beyond normal C build support.

Its Linux-kernel header-export use case is exactly the kind of quiet infrastructure job package maintainers care about: remove implementation-only conditional sections, preserve line-oriented source structure, and keep generated user-facing source understandable.

Timeline

• 2.9BSD: Manual says the `unifdef` command appeared.
• FreeBSD 4.7: Manual says ANSI C support was added.
• 2015: Official manual page is dated December 3, 2015.
• Current project page: Release 2.12 archives are published on dotat.at.
• Current README: GitHub is maintained as a collaboration mirror, while release downloads remain on dotat.at.

Related projects

• The manual lists `cpp(1)` and `diff(1)` as related tools.
• The official page cites Linux kernel header export as a real-world use.
• The official page also mentions use with LaTeX, showing text-mode uses outside C.

Sources

• https://dotat.at/prog/unifdef/
• https://dotat.at/prog/unifdef/unifdef.txt
• https://github.com/fanf2/unifdef#readme
• input.source_facts.package-manager