<!--

  Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 The SCons Foundation

  Permission is hereby granted, free of charge, to any person obtaining
  a copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-->

  <para>

  &SCons; provides a number of platform-independent functions,
  called <literal>factories</literal>,
  that perform common file system manipulations
  like copying, moving or deleting files and directories,
  or making directories.
  These functions are <literal>factories</literal>
  because they don't perform the action
  at the time they're called,
  they each return an &Action; object
  that can be executed at the appropriate time.

  </para>

  <section>
  <title>Copying Files or Directories:  The &Copy; Factory</title>

    <para>

    Suppose you want to arrange to make a copy of a file,
    and don't have a suitable pre-existing builder.
    <footnote>
    <para>
    Unfortunately, in the early days of SCons design,
    we used the name &Copy; for the function that
    returns a copy of the environment,
    otherwise that would be the logical choice for
    a Builder that copies a file or directory tree
    to a target location.
    </para>
    </footnote>
    One way would be to use the &Copy; action factory
    in conjunction with the &Command; builder:

    </para>

    <programlisting>
        Command("file.out", "file.in", Copy("$TARGET", "$SOURCE"))
    </programlisting>

    <para>

    Notice that the action returned by the &Copy; factory
    will expand the &cv-link-TARGET; and &cv-link-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:

    </para>

    <screen>
       % <userinput>scons -Q</userinput>
       Copy("file.out", "file.in")
    </screen>

    <para>

    You can, of course, name a file explicitly
    instead of using &cv-TARGET; or &cv-SOURCE;:

    </para>

    <programlisting>
      Command("file.out", [], Copy("$TARGET", "file.in"))
    </programlisting>

    <para>

    Which executes as:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Copy("file.out", "file.in")
    </screen>

    <para>

    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:

    </para>

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

    <para>

    The output then looks like:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Copy("tempfile", "file.in")
      modify tempfile
      Copy("file.out", "tempfile")
    </screen>

  </section>

  <section>
  <title>Deleting Files or Directories:  The &Delete; Factory</title>

    <para>

    If you need to delete a file,
    then the &Delete; factory
    can be used in much the same way as
    the &Copy; factory.
    For example, if we want to make sure that
    the temporary file
    in our last example doesn't exist before
    we copy to it,
    we could add &Delete; to the beginning
    of the command list:

    </para>

    <programlisting>
      Command("file.out", "file.in",
              [
                Delete("tempfile"),
                Copy("tempfile", "$SOURCE"),
                "modify tempfile",
                Copy("$TARGET", "tempfile"),
              ])
    </programlisting>

    <para>

    Which then executes as follows:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Delete("tempfile")
      Copy("tempfile", "file.in")
      modify tempfile
      Copy("file.out", "tempfile")
    </screen>

    <para>

    Of course, like all of these &Action; factories,
    the &Delete; factory also expands
    &cv-link-TARGET; and &cv-link-SOURCE; variables appropriately.
    For example:

    </para>

    <programlisting>
      Command("file.out", "file.in",
              [
                Delete("$TARGET"),
                Copy("$TARGET", "$SOURCE")
              ])
    </programlisting>

    <para>

    Executes as:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Delete("file.out")
      Copy("file.out", "file.in")
    </screen>

    <para>

    Note, however, that you typically don't need to
    call the &Delete; factory explicitly in this way;
    by default, &SCons; deletes its target(s)
    for you before executing any action.

    </para>

    <para>

    One word of caution about using the &Delete; factory:
    it has the same variable expansions available
    as any other factory, including the &cv-SOURCE; variable.
    Specifying <literal>Delete("$SOURCE")</literal>
    is not something you usually want to do!

    </para>

  </section>

  <section>
  <title>Moving (Renaming) Files or Directories:  The &Move; Factory</title>

    <para>

    The &Move; factory
    allows you to rename a file or directory.
    For example, if we don't want to copy the temporary file,
    we could use:

    </para>

    <programlisting>
      Command("file.out", "file.in",
              [
                Copy("tempfile", "$SOURCE"),
                "modify tempfile",
                Move("$TARGET", "tempfile"),
              ])
    </programlisting>

    <para>

    Which would execute as:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Copy("tempfile", "file.in")
      modify tempfile
      Move("file.out", "tempfile")
    </screen>

  </section>

  <section>
  <title>Updating the Modification Time of a File:  The &Touch; Factory</title>

    <para>

    If you just need to update the
    recorded modification time for a file,
    use the &Touch; factory:

    </para>

    <programlisting>
      Command("file.out", "file.in",
              [
                Copy("$TARGET", "$SOURCE"),
                Touch("$TARGET"),
              ])
    </programlisting>

    <para>

    Which executes as:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Copy("file.out", "file.in")
      Touch("file.out")
    </screen>

  </section>

  <section>
  <title>Creating a Directory:  The &Mkdir; Factory</title>

    <para>

    If you need to create a directory,
    use the &Mkdir; factory.
    For example, if we need to process
    a file in a temporary directory
    in which the processing tool
    will create other files that we don't care about, 
    you could use:

    </para>

    <programlisting>
      Command("file.out", "file.in",
              [
                Delete("tempdir"),
                Mkdir("tempdir"),
                Copy("tempdir/${SOURCE.file}", "$SOURCE"),
                "process tempdir",
                Move("$TARGET", "tempdir/output_file"),
                Delete("tempdir"),
              ])
    </programlisting>

    <para>

    Which executes as:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Delete("tempdir")
      Mkdir("tempdir")
      Copy("tempdir/file.in", "file.in")
      process tempdir
      Move("file.out", "tempdir/output_file")
      scons: *** [file.out] tempdir/output_file: No such file or directory
    </screen>

  </section>

  <section>
  <title>Changing File or Directory Permissions:  The &Chmod; Factory</title>

    <para>

    To change permissions on a file or directory,
    use the &Chmod; factory.
    The permission argument uses POSIX-style
    permission bits and should typically
    be expressed as an octal,
    not decimal, number:

    </para>

    <programlisting>
      Command("file.out", "file.in",
              [
                Copy("$TARGET", "$SOURCE"),
                Chmod("$TARGET", 0755),
              ])
    </programlisting>

    <para>

    Which executes:

    </para>

    <screen>
      % <userinput>scons -Q</userinput>
      Copy("file.out", "file.in")
      Chmod("file.out", 0755)
    </screen>

  </section>

  <section>
  <title>Executing an action immediately:  the &Execute; Function</title>

    <para>

    We've been showing you how to use &Action; factories
    in the &Command; function.
    You can also execute an &Action; returned by a factory
    (or actually, any &Action;)
    at the time the &SConscript; file is read
    by using the &Execute; function.
    For example, if we need to make sure that
    a directory exists before we build any targets,

    </para>

    <programlisting>
      Execute(Mkdir('/tmp/my_temp_directory'))
    </programlisting>

    <para>

    Notice that this will
    create the directory while
    the &SConscript; file is being read:

    </para>

    <screen>
      % <userinput>scons</userinput>
      scons: Reading SConscript files ...
      Mkdir("/tmp/my_temp_directory")
      scons: done reading SConscript files.
      scons: Building targets ...
      scons: `.' is up to date.
      scons: done building targets.
    </screen>

    <para>

    If you're familiar with Python,
    you may wonder why you would want to use this
    instead of just calling the native Python
    <function>os.mkdir()</function> function.
    The advantage here is that the &Mkdir;
    action will behave appropriately if the user
    specifies the &SCons; <option>-n</option> or
    <option>-q</option> options--that is,
    it will print the action but not actually
    make the directory when <option>-n</option> is specified,
    or make the directory but not print the action
    when <option>-q</option> is specified.

    </para>

    <para>

    The &Execute; function returns the exit status
    or return value of the underlying action being executed.
    It will also print an error message if the action
    fails and returns a non-zero value.
    &SCons; will <emphasis>not</emphasis>, however,
    actually stop the build if the action fails.
    If you want the build to stop
    in response to a failure in an action called by &Execute;,
    you must do so by explicitly
    checking the return value
    and calling the &Exit; function
    (or a Python equivalent):

    </para>

    <programlisting>
    if Execute(Mkdir('/tmp/my_temp_directory')):
        # A problem occurred while making the temp directory.
        Exit(1)
    </programlisting>

  </section>
