Copying Files or Directories: The Copy Factory

Suppose you want to arrange to make a copy of a file, and the Install builder isn't appropriate because it may make a hard link on POSIX systems. One way would be to use the Copy action factory in conjunction with the Command builder:

        Command("file.out", "file.in", Copy("$TARGET", "$SOURCE"))
    

Notice that the action returned by the Copy factory will expand the $TARGET and $SOURCE strings at the time file.out is built, and that the order of the arguments is the same as that of a builder itself--that is, target first, followed by source:

       % scons -Q
       Copy("file.out", "file.in")
    

You can, of course, name a file explicitly instead of using $TARGET or $SOURCE:

      Command("file.out", [], Copy("$TARGET", "file.in"))
    

Which executes as:

      % scons -Q
      Copy("file.out", "file.in")
    

The usefulness of the Copy factory becomes more apparent when you use it in a list of actions passed to the Command builder. For example, suppose you needed to run a file through a utility that only modifies files in-place, and can't "pipe" input to output. One solution is to copy the source file to a temporary file name, run the utility, and then copy the modified temporary file to the target, which the Copy factory makes extremely easy:

      Command("file.out", "file.in",
              [
                Copy("tempfile", "$SOURCE"),
                "modify tempfile",
                Copy("$TARGET", "tempfile"),
              ])
    

The output then looks like:

      % scons -Q
      Copy("tempfile", "file.in")
      modify tempfile
      Copy("file.out", "tempfile")