New features in POSIX 2024

The 2024 POSIX standard adds the following features to the 2017 revision.

The standard allows different implementations of some features: these notes reference the choices made in pdpmake.

• 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 allows targets to be updated concurrently. It is accepted by pdpmake but doesn't cause jobs to be run in parallel, as is permitted by the standard.
• The .NOTPARALLEL and .WAIT special targets control the execution of parallel jobs. They are permitted in pdpmake (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• Prerequisites of the .PHONY special target are always treated as being out-of-date.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• Missing or out-of-date include files are rebuilt if an appropriate rule can be found. In pdpmake 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• The $^ and $+ internal macros evaluate to all prerequisites of the current target (not just out-of-date ones, as with $?).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.
• The CURDIR macro is set to the current directory during program start up.
• The default rules have changed: Fortran is no longer supported and the C compiler defaults to 'c17'.