Automatic Retrieval of SCCS Files

When source files are named in the dependency list, make treats them like any other target. Because the source file is presumed to be present in the directory, there is no need to add an entry for it to the makefile.

When a target has no dependencies, but is present in the directory, make assumes that file is up to date. If, however, a source file is under SCCS control, make does some additional checking to ensure that the source file is up to date. If the file is missing, or if the history file is newer, make automatically issues the following command to retrieve the most recent version:

sccs get -s filename -Gfilename 

With other versions of make, automatic sccs retrieval was a feature only of certain implicit rules. Also, unlike earlier versions, make only looks for history (s.) files in the sccs directory; history files in the current working directory are ignored.

However, if the source file is writable by anyone, make does not retrieve a new version.

$ ls SCCS/* 
SCCS/s.functions.c
$ rm -f functions.c 
$ make functions 
sccs get -s functions.c -Gfunctions.c 
cc -o functions functions.c 

make checks the time stamp of the retrieved version against the time stamp of the history file. It does not check to see if the version present in the directory is the most recently checked-in version. So, if someone had done a get by date (sccs get -c), make would not discover this fact, and you might unwittingly build an older version of the program or object file. To be absolutely sure that you are compiling the latest version, you can precede make with an sccs get SCCS` or an sccs clean command.

Suppressing SCCS Retrieval

The command for retrieving SCCS files is specified in the rule for the .SCCS_GET special target in the default makefile. To suppress automatic retrieval, simply add an entry for this target with an empty rule to your makefile:

# Suppress sccs retrieval. 
       	.SCCS_GET: