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Features of GNU make
Here is a summary of the features of GNU make, for comparison with and credit to other versions of make. We consider the features of make in 4.2 BSD systems
as a baseline. If you are concerned with writing portable makefiles, you should use only the features of make not listed here or in section Incompatibilities and
Missing Features.
Many features come from the version of make in System V.
The VPATH variable and its special meaning. See section Searching Directories for Dependencies. This feature exists in System V make, but is
undocumented. It is documented in 4.3 BSD make (which says it mimics System V's VPATH feature).
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Included makefiles. See section Including Other Makefiles. Allowing multiple files to be included with a single directive is a GNU extension.●
Variables are read from and communicated via the environment. See section Variables from the Environment.●
Options passed through the variable MAKEFLAGS to recursive invocations of make. See section Communicating Options to a Sub-make.●
The automatic variable $% is set to the member name in an archive reference. See section Automatic Variables.●
The automatic variables $@, $*, $<, $%, and $? have corresponding forms like $(@F) and $(@D). We have generalized this to $^ as an obvious
extension. See section Automatic Variables.
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Substitution variable references. See section Basics of Variable References.●
The command-line options `-b' and `-m', accepted and ignored. In System V make, these options actually do something.●
Execution of recursive commands to run make via the variable MAKE even if `-n', `-q' or `-t' is specified. See section Recursive Use of make.●
Support for suffix `.a' in suffix rules. See section Suffix Rules for Archive Files. This feature is obsolete in GNU make, because the general feature of
rule chaining (see section Chains of Implicit Rules) allows one pattern rule for installing members in an archive (see section Implicit Rule for Archive
Member Targets) to be sufficient.
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The arrangement of lines and backslash-newline combinations in commands is retained when the commands are printed, so they appear as they do in the
makefile, except for the stripping of initial whitespace.
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The following features were inspired by various other versions of make. In some cases it is unclear exactly which versions inspired which others.
Pattern rules using `%'. This has been implemented in several versions of make. We're not sure who invented it first, but it's been spread around a bit. See
section Defining and Redefining Pattern Rules.
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Rule chaining and implicit intermediate files. This was implemented by Stu Feldman in his version of make for AT&T Eighth Edition Research Unix,
and later by Andrew Hume of AT&T Bell Labs in his mk program (where he terms it "transitive closure"). We do not really know if we got this from
either of them or thought it up ourselves at the same time. See section Chains of Implicit Rules.
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The automatic variable $^ containing a list of all dependencies of the current target. We did not invent this, but we have no idea who did. See section
Automatic Variables. The automatic variable $+ is a simple extension of $^.
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The "what if" flag (`-W' in GNU make) was (as far as we know) invented by Andrew Hume in mk. See section Instead of Executing the Commands.●
The concept of doing several things at once (parallelism) exists in many incarnations of make and similar programs, though not in the System V or BSD
implementations. See section Command Execution.
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Modified variable references using pattern substitution come from SunOS 4. See section Basics of Variable References. This functionality was provided
in GNU make by the patsubst function before the alternate syntax was implemented for compatibility with SunOS 4. It is not altogether clear who
inspired whom, since GNU make had patsubst before SunOS 4 was released.
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The special significance of `+' characters preceding command lines (see section Instead of Executing the Commands) is mandated by IEEE Standard
1003.2-1992 (POSIX.2).
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The `+=' syntax to append to the value of a variable comes from SunOS 4 make. See section Appending More Text to Variables.●
The syntax `archive(mem1 mem2...)' to list multiple members in a single archive file comes from SunOS 4 make. See section Archive Members as
Targets.
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The -include directive to include makefiles with no error for a nonexistent file comes from SunOS 4 make. (But note that SunOS 4 make does not
allow multiple makefiles to be specified in one -include directive.) The same feature appears with the name sinclude in SGI make and perhaps
others.
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The remaining features are inventions new in GNU make:
Use the `-v' or `--version' option to print version and copyright information.●
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