This allows rules to act almost as procedure calls. If it doesn't find one, it recursively attempts to update the dependencies tclIndex and sources . The effect is exactly the same as if tclIndex and sources had been the goals in the first place. This is less efficient, but often more convenient. Since, however, the latter file does not exist, tclmake pattern-matches against all files in the SCCS directory, with the result that all files with a new SCCS file will be updated.
Suffix rules A suffix rule consists of two concatenated file suffixes.
The double-colon means that this rule is a terminator rule. In other words, use the double-colon when a dependency is a file that must exist, and cannot be produced from other files. Option rules One of the few extensions tclmake makes to regular make is the ability to define command-line options in the tclmakefile itself. To do so, simply define a rule that has targets beginning with a leading dash, and with no dependencies. If any of those targets are specified on the command line, the rule will be run after updating all other targets.