There are two occasions when &SCons; will, by default, remove target files. The first is when &SCons; determines that an target file needs to be rebuilt and removes the existing version of the target before executing The second is when &SCons; is invoked with the -c option to "clean" a tree of its built targets. These behaviours can be suppressed with the &Precious; and &NoClean; functions, respectively.

By default, &SCons; removes targets before building them. Sometimes, however, this is not what you want. For example, you may want to update a library incrementally, not by having it deleted and then rebuilt from all of the constituent object files. In such cases, you can use the &Precious; method to prevent &SCons; from removing the target before it is built: env = Environment(RANLIBCOM='') lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c']) env.Precious(lib) Although the output doesn't look any different, &SCons; does not, in fact, delete the target library before rebuilding it: % scons -Q cc -o f1.o -c f1.c cc -o f2.o -c f2.c cc -o f3.o -c f3.c ar rc libfoo.a f1.o f2.o f3.o &SCons; will, however, still delete files marked as &Precious; when the -c option is used.

By default, &SCons; removes all built targets when invoked with the -c option to clean a source tree of built tragets. Sometimes, however, this is not what you want. For example, you may want to remove only intermediate generated files (such as object files), but leave the final targets (the libraries) untouched. In such cases, you can use the &NoClean; method to prevent &SCons; from removing a target during a clean: env = Environment(RANLIBCOM='') lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c']) env.NoClean(lib) Notice that the libfoo.a is not listed as a removed file: % scons -Q cc -o f1.o -c f1.c cc -o f2.o -c f2.c cc -o f3.o -c f3.c ar rc libfoo.a f1.o f2.o f3.o % scons -c scons: Reading SConscript files ... scons: done reading SConscript files. scons: Cleaning targets ... Removed f1.o Removed f2.o Removed f3.o scons: done cleaning targets.