4.2 Makefile syntax

`Makefile's have a rather particular syntax that can trouble new users. There are many implementations of make, some of which provide non-portable extensions. An abridged description of the syntax follows which, for portability, may be stricter than you may be used to.

Comments start with a `#' and continue until the end of line. They may appear anywhere except in command sequences--if they do, they will be interpreted by the shell running the command. The following `Makefile' shows three individual targets with dependencies on each:

target1: dep1 dep2 ... depN <tab> cmd1 <tab> cmd2 <tab> ... <tab> cmdN target2: dep4 dep5 <tab> cmd1 <tab> cmd2 dep4 dep5: <tab> cmd1

Target rules start at the beginning of a line and are followed by a colon. Following the colon is a whitespace separated list of dependencies. A series of lines follow which contain shell commands to be run by a sub-shell (the default is the Bourne shell). Each of these lines must be prefixed by a horizontal tab character. This is the most common mistake made by new make users.

These commands may be prefixed by an `@' character to prevent make from echoing the command line prior to executing it. They may also optionally be prefixed by a `-' character to allow the rule to continue if the command returns a non-zero exit code. The combination of both characters is permitted.