Write Makefile Compatible with Both GNU `make` and BSD `make`

BSD make is simple, but GNU make is more popular due to Linux’s popularity.Thus I prefer to write Makefile compatible with both versions.

Syntax

The following syntax is valid in both GNU make and BSD make.

include config.mk

# variable declaration (this is a comment)
PREFIX = /usr/local

# First target is the default target which will be invoked when typing `make`.
all: this-is-a-target another-target

this-is-a-target:
        echo command
        echo `echo command substitution`
        @echo not echo the command line to screen
        -echo keep going even if command returns a nonzero status

another-target: sourcefile
        echo will only run if sourcefile timestamp is newer
        echo ${PREFIX}

BSD vs. GNU

BSD Make just knows about dependencies, targets, rules and macros.GNU Make adds built in rules to that mix to make it easier for the developer.

It turns out that details of systems are conflicting and cannot be known in advance.BSD Make deals with system dependencies by having the system define its parameters.GNU Make’s built in rules turn out to be inadequate.

– kbw

When using bsd.*.mk, each Makefile can build only one program or library.

…

The file bsd.port.mk is at the center of FreeBSD Ports,the system that builds software packages for FreeBSD.(NetBSD pkgsrc calls this file bsd.pkg.mk.)

– George Koehler

Most of openbsds simple Makefiles are compatible with bmakebut if it gets a little bit more complicatedthere are small differences that break the build.

… the openbsd Makefiles /usr/share/mk … are not really portableand use openbsd specific binaries like lorder and tsort with the openbsd specific -q flag.

And most software is using GNU Make,I think it would be way more work to use bsd makefiles on linux targets,they are not really written to be portable.

– Duncaen

Under debian, BSD make is available as the bmake package.And FreeBSD makefile templates for bmake are available as the freebsd-mk package.

Bonus: Plan9 mk

mk in Plan9 is similar to BSD make, with fewer rules.

The main difference is templating:

• BSD Makefile supports standard templates .include <bsd.prog.mk> and nonstandard templates .include "/path/to/included.mk" or include filename,
• Plan9 Makefile does not support standard templates, and it uses different syntax for nonstandard templates </path/to/included.mk.
• Plan9 Makefile also supports including command line output (<|cat /path/to/included.mk>).

Plan9 also supports using different shells within a single mkfile:

MKSHELL=/bin/rc
use-rc:V:
    for(i in a b c) echo $i

MKSHELL=sh
use-sh:V:
    for i in a b c; do echo $i; done