Environment variables

Environment variables are read and added to the macro definitions each time make executes. Precedence is a prime consideration in doing this properly. The following describes make's interaction with the environment.

make automatically defines a macro, MAKEFLAGS, containing the command-line option flags given in the invocation of make. The intent of the MAKEFLAGS macro, upon startup, is to set environment variables to be used by successive invocations of make.

When executed, make assigns macro definitions in the following order:

1. Read the MAKEFLAGS environment variable. If it is not present or null, the internal make variable MAKEFLAGS is set to the null string. Otherwise, each letter in MAKEFLAGS is assumed to be an input flag argument and is processed as such. (The only exceptions are the -f, -p, and -r flags.)

2. Read the internal list of macro definitions.

3. Read the environment. The environment variables are treated as macro definitions and marked as exported (in the shell sense).

4. Read the makefile(s). The assignments in the makefile(s) override the environment. This order is chosen so that it is possible to know what to expect by reading the makefile being executed. However, if the -e command-line flag is used, the environment overrides the makefile assignments. Therefore, if make -e ... is typed, the variables in the environment override the definitions in the makefile. Also, MAKEFLAGS overrides the environment if assigned. This is useful for further invocations of make from the current makefile.

• internal definitions

• environment

• makefile(s)

• command line

• internal definitions

• makefile(s)

• environment

• command line

This order is general enough to allow a programmer to define a makefile or set of makefiles whose parameters are dynamically definable.