A makefile is made of four types of lines:
Dependency lines
Creation commands
Variable assignments
Comments, include statements and conditional directives
A dependency line is a list of one or more targets, an operator (:, ::, or !), and a list of zero or more sources. Sources may contain wildcards and certain local variables.
A creation command is a regular shell command preceded by a tab. In addition, if the first two characters after the tab (and other whitespace) are a combination of @ or -, PMake will cause the command to not be printed (if the character is @) or errors from it to be ignored (if -). A blank line, dependency line or variable assignment terminates a creation script. There may be only one creation script for each target with a : or ! operator.
Variables are places to store text. They may be unconditionally assigned-to using the = operator, appended-to using the += operator, conditionally (if the variable is undefined) assigned-to with the ?= operator, and assigned-to with variable expansion with the := operator. The output of a shell command may be assigned to a variable using the != operator. Variables may be expanded (their value inserted) by enclosing their name in parentheses or curly braces, preceded by a dollar sign. A dollar sign may be escaped with another dollar sign. Variables are not expanded if PMake does not know about them. There are seven local variables: .TARGET, .ALLSRC, .OODATE, .PREFIX, .IMPSRC, .ARCHIVE, and .MEMBER. Four of them (.TARGET, .PREFIX, .ARCHIVE, and .MEMBER) may be used to specify “dynamic sources”. Variables are good. Know them. Love them. Live them.
Debugging of makefiles is best accomplished using the -n,
-d m, and -p 2 flags.