Public domain POSIX make

This is a public domain implementation of make which follows the POSIX standard.

If you've got here I assume you know what make is and why you might want to use it. If not, Chris Wellons has a nice Tutorial on Portable Makefiles.

The code is based on Neil Russell's public domain make, as submitted to the Usenet newsgroups net.sources and mod.sources in 1986. The basic data structures and algorithms remain but everything else has changed. This version is also dedicated to the public domain.

The problem with make is that it's a tool for developers, and developers like to tinker with their tools. There are therefore many slightly different versions of make around. POSIX attempts to standardise their common behaviour but leaves a lot of the details unspecified or implementation dependent. It's also rather lax, in that it allows extensions to exist provided they don't interfere with the specified functionality.

This version tries to stick to the POSIX standard. The default build from source includes a number of extensions but a key feature of the program is that it can be switched to a strictly POSIX-compliant mode at runtime. This can be achieved in several ways:

• The POSIX approach is to provide the special target .POSIX as the first non-comment line of the first makefile to be processed.
• The non-standard --posix command line option. This must be the first given on the command line.
• The non-standard PDPMAKE_POSIXLY_CORRECT environment variable. If this is set to any value (even an empty string) all extensions are disabled.

Extensions from a future POSIX standard are included. These remain subject to change until the standard is finally published.

• Nested macro expansion can be used to build the name of a macro from the contents of other macros. This is crucial for such tricks as implementing the Game of Life in a makefile.
• The -j maxjobs command line option is accepted but doesn't cause jobs to be run in parallel, as is permitted by the proposed standard.
• The .NOTPARALLEL and .WAIT special targets are permitted (but have no effect, see above).
• Prerequisites of the .PHONY special target are always treated as being out-of-date.
• More than one file can be specified on each include line.
• Missing include files can be ignored with the -include variant of include. This can be handy when using the automatic dependency tracking feature of compilers.
• Missing or out-of-date include files are rebuilt if an appropriate rule can be found. This is done using the "immediate remaking" method from SunPro make rather than the "delayed remaking" used by GNU make.
• The $^ and $+ internal macros evaluate to all prerequisites of the current target (not just out-of-date ones, as with $?). $^ removes duplicated prerequisites from the list, $+ doesn't.
• If no MAKE environment variable is provided the MAKE macro is initialised from argv[0], with a relative path converted to absolute.
• The macro assignments ::=, :::=, +=, ?= and != are permitted.
• Pattern macros extend the standard suffix substitution in macro expansion to allow changes to prefixes as well. For example:

     SRC = src/util.c src/main.c
     OBJ = $(SRC:src/%.c=obj/%.o)
  

• An escaped newline within a macro expansion on a command line is replaced by a space.

Some additional extensions are also provided. These are all compatible with GNU make, though some are supported by other implementations.

• The -C directory command line option changes the current working directory.
• Double colon rules are allowed. POSIX excludes them on the grounds that they're a BSD extension. I'm not sure that's correct, but whatever.
• A limited set of conditional statements is allowed:
  • ifdef
  • ifndef
  • else
  • endif
• Archive members can be specified using the form lib.a(mem1.o mem2.o...).
• The macro assignment := is permitted. It is equivalent to ::= in POSIX.
• Chained inference rules can be used when searching for the prerequisites of a target. Thus, if there are inference rules .p.q and .q.r and the file thing.p exists, make is able to deduce how to create thing.r.
• The wildcards '*', '?' and '[]' can be used in the targets and prerequisites of target rules.
• '#' on a command line or in a macro expansion doesn't indicate the start of a comment.
• Duplicated prerequisites are removed when the internal macro $? is expanded.
• An include line with no files specified is silently ignored. At least one blank must follow the include for the line to be valid.

To make POSIX mode more convenient to use certain inconvenient limitations can be relaxed through the use of pragmas. These can be specified in two ways:

• On the command line with the -x flag.
• In makefiles with the .PRAGMA special target.

Available pragmas are:

macro_name

Allow '-' as a valid character in macro names.

target_name

Allow '-' and '/' as a valid characters in target names.

command_comment

Don't treat the '#' character as introducing a comment in commands in target or inference rules.

empty_suffix

Permit an empty suffix in macro expansions of the form $(VAR:=.c).

posix_202x

Enforce the future POSIX 202X standard rather than the current POSIX 2017. In this case the macro_name and target_name pragmas aren't required as the future standard will allow the additional characters.

Specifying the .PRAGMA special target with no prerequisites restores the default behaviour.

The most recent source tarball is pdpmake-1.4.1.tgz. The release notes describe recent changes.

Source is also available in a Git repository mirrored on GitHub, Gitlab and with (IPv6 only):

   git clone git://git.frippery.org/pdpmake

Future POSIX and non-POSIX extensions can be enabled separately by setting the build flags ENABLE_FEATURE_MAKE_EXTENSIONS and ENABLE_FEATURE_MAKE_POSIX_202X to 1. Setting both flags to 1 is equivalent to the default configuration, except that the future POSIX standard is enforced in POSIX mode rather than the current standard.

Bug reports can be submitted via GitHub, GitLab or by email to the address below.

Remember, though, this is just a bunch of zeroes and ones you happened to find on the internet. If it does anything useful that's an unexpected bonus.