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<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
    <!ENTITY % scons SYSTEM "../scons.mod">
    %scons;
    
    <!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
    %builders-mod;
    <!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
    %functions-mod;
    <!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
    %tools-mod;
    <!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
    %variables-mod;

]>

<chapter id="chap-factories"
         xmlns="http://www.scons.org/dbxsd/v1.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">
<title>Platform-Independent File System Manipulation</title>

<!--

  Copyright (c) 2001 - 2014 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,
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  permit persons to whom the Software is furnished to do so, subject to
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  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>

    <scons_example name="factories_Copy1">
      <file name="SConstruct" printme="1">
Command("file.out", "file.in", Copy("$TARGET", "$SOURCE"))
      </file>
      <file name="file.in">file.in</file>
    </scons_example>

    <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>

    <scons_output example="factories_Copy1" suffix="1">
       <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <para>

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

    </para>

    <scons_example name="factories_Copy2">
      <file name="SConstruct" printme="1">
Command("file.out", [], Copy("$TARGET", "file.in"))
      </file>
      <file name="file.in">file.in</file>
    </scons_example>

    <para>

    Which executes as:

    </para>

    <scons_output example="factories_Copy2" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <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>

    <scons_example name="factories_Copy3">
      <file name="S" printme="1">
Command("file.out", "file.in",
        [
          Copy("tempfile", "$SOURCE"),
          "modify tempfile",
          Copy("$TARGET", "tempfile"),
        ])
      </file>
      <file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
      </file>
      <file name="file.in">file.in</file>
      <file name="modify" chmod="0755">
touch $*
      </file>
    </scons_example>

    <para>

    The output then looks like:

    </para>

    <scons_output example="factories_Copy3" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </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>

    <scons_example name="factories_Delete1">
      <file name="S" printme="1">
Command("file.out", "file.in",
        [
          Delete("tempfile"),
          Copy("tempfile", "$SOURCE"),
          "modify tempfile",
          Copy("$TARGET", "tempfile"),
        ])
      </file>
      <file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
      </file>
      <file name="file.in">file.in</file>
      <file name="modify" chmod="0755">
touch $*
      </file>
    </scons_example>

    <para>

    Which then executes as follows:

    </para>

    <scons_output example="factories_Delete1" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <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>

    <scons_example name="factories_Delete2">
      <file name="SConstruct" printme="1">
Command("file.out", "file.in",
        [
          Delete("$TARGET"),
          Copy("$TARGET", "$SOURCE")
        ])
      </file>
      <file name="file.in">file.in</file>
    </scons_example>

    <para>

    Executes as:

    </para>

    <scons_output example="factories_Delete2" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

    <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>

    <scons_example name="factories_Move">
      <file name="S" printme="1">
Command("file.out", "file.in",
        [
          Copy("tempfile", "$SOURCE"),
          "modify tempfile",
          Move("$TARGET", "tempfile"),
        ])
      </file>
      <file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
      </file>
      <file name="file.in">file.in</file>
      <file name="modify" chmod="0755">
touch $*
      </file>
    </scons_example>

    <para>

    Which would execute as:

    </para>

    <scons_output example="factories_Move" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </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>

    <scons_example name="factories_Touch">
      <file name="S" printme="1">
Command("file.out", "file.in",
        [
          Copy("$TARGET", "$SOURCE"),
          Touch("$TARGET"),
        ])
      </file>
      <file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
      </file>
      <file name="file.in">file.in</file>
    </scons_example>

    <para>

    Which executes as:

    </para>

    <scons_output example="factories_Touch" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </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>

    <scons_example name="factories_Mkdir">
      <file name="S" printme="1">
Command("file.out", "file.in",
        [
          Delete("tempdir"),
          Mkdir("tempdir"),
          Copy("tempdir/${SOURCE.file}", "$SOURCE"),
          "process tempdir",
          Move("$TARGET", "tempdir/output_file"),
          Delete("tempdir"),
        ])
      </file>
      <file name="SConstruct">
env = DefaultEnvironment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
SConscript('S')
      </file>
      <file name="file.in">file.in</file>
      <file name="process" chmod="0755">
touch $*
      </file>
    </scons_example>

    <para>

    Which executes as:

    </para>

    <scons_output example="factories_Mkdir" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </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>

    <scons_example name="factories_Chmod">
      <file name="SConstruct" printme="1">
Command("file.out", "file.in",
        [
          Copy("$TARGET", "$SOURCE"),
          Chmod("$TARGET", 0755),
        ])
      </file>
      <file name="file.in">file.in</file>
    </scons_example>

    <para>

    Which executes:

    </para>

    <scons_output example="factories_Chmod" suffix="1">
      <scons_output_command>scons -Q</scons_output_command>
    </scons_output>

  </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>

    <scons_example name="factories_Execute">
      <file name="SConstruct" printme="1">
Execute(Mkdir('__ROOT__/tmp/my_temp_directory'))
      </file>
    </scons_example>

    <para>

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

    </para>

    <scons_output example="factories_Execute" suffix="1">
      <scons_output_command>scons</scons_output_command>
    </scons_output>

    <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>

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

  </section>

</chapter>