# The Extract System

The extract system provides an interface between the revision control system (currently Subversion) and the build system. Where appropriate, it extracts code from the repository and other user-defined locations to a directory tree suitable for feeding into the build system. In this chapter, we shall use many examples to explain how to use the extract system. At the end of this chapter, you will be able to extract code from the local file system as well as from different branches of different repository URLs. You will also learn how to mirror code to a remote machine. Finally, you will be given an introduction on how to specify configurations for the build system via the extract configuration file. (For further information on the build system, please see the next chapter The Build System.) The last section of the chapter tells you what you can do in the case when Subversion is not available.

## The Extract Command

To invoke the extract system, simply issue the command:

    fcm extract

By default, the extract system searches for an extract configuration file "ext.cfg" in "$PWD" and then "$PWD/cfg". If an extract configuration file is not found in these directories, the command fails with an error. If an extract configuration file is found, the system will use the configuration specified in the file to perform the current extraction.

If the destination of the extraction does not exist, the system performs a new full extraction to the destination. If a previous extraction already exists at the destination, the system performs an incremental extraction, updating any modifications if necessary. If a full (fresh) extraction is required for whatever reason, you can invoke the extract system using the "-f" option, (i.e. the command becomes "fcm extract -f"). For further information on the extract command, please see FCM Command Reference > fcm extract.

## Simple Usage

The extract configuration file is the main user interface of the extract system. It is a line based text file. For a complete set of extract configuration file declarations, please refer to the Annex: Declarations in FCM extract configuration file.

### Extract from a local path

A simple example of a basic extract configuration file is given below:

Extract configuration example 1 - extract from a local path
    cfg::type         ext       # line 1
    cfg::version      1.0       # line 2
                                # line 3
    dest::rootdir     $PWD      # line 4
                                # line 5
    repos::var::user  $HOME/var # line 6
                                # line 7
    expsrc::var::user code      # line 8

The above demonstrates how to use the extract system to extract code from a local user directory. Here is an explanation of what each line does:

- line 1: the label "CFG::TYPE" declares the type of the configuration file. The value "ext" tells the system that it is an extract configuration file.
- line 2: the label "CFG::VERSION" declares the version of the extract configuration file. The current default is "1.0". Although it is not currently used, if we have to change the format of the configuration file at a later stage, we shall be able to use this number to determine whether we are reading a file with an older format or one with a newer format.
- line 3: a blank line or a line beginning with a "#" is a comment, and is ignored by the interpreter.
- line 4: the label "DEST::ROOTDIR" declares the destination root directory of this extraction. The value "$PWD" expands to the current working directory.
- line 5: comment line, ignored.
- line 6: the label "REPOS::<pck>::<branch>" declares the top level URL or path of a repository. The package name of the repository is given by <pck>. In our example, we choose "var" as the name of the package. (You can choose any name you like, however, it is usually sensible to use a package name that matches the name of the project or system you are working with.) The branch name in the repository is given by <branch>. (Again, you can choose any name you like, however, it is usually sensible to use a name such as "trunk", "user" or something that matches your branch name.) In our example, the word "user" is normally used to denote a local user directory. Hence the statement declares that the repository path for the "var" package in the "user" branch can be found at "$HOME/var".
- line 7: comment line, ignored.
- line 8: the label "EXPSRC::<pck>::<branch>" declares an "expandable" source directory for the package <pck> in the branch <branch>. In our example, the package name is "var", and the branch name is "user". These match the package and the branch names of the repository declaration in line 6. It means that the source directory declaration is associated with the path "$HOME/var". The value of the declaration "code" is therefore a sub-directory under "$HOME/var". By declaring a source directory using an "expsrc" label, the system automatically searches for all sub-directories (recursively) under the declared source directory.

Invoking the extract system using the above configuration file will "extract" all sub-directories under "$HOME/var/code" to "$PWD/src/var/code". Note: the extract system ignores all hidden files, (i.e. directories and files beginning with a "."). It will write a build configuration file to "$PWD/cfg/bld.cfg". The configuration used for this extraction will be written to the configuration file at "$PWD/cfg/ext.cfg".

Note - incremental extraction
Suppose you have already performed an extraction using the above configuration file. At a later time, you have made some changes to some of the files in the source directory. Re-running the extract system on the same configuration will trigger an incremental extraction. In an incremental extraction, the system will update only those files that are modified. In exact words, the system checks the modification time of each file in the source and destination. If a source file is newer than its corresponding destination file, it checks whether the content differs. The destination is only updated if its content differs from the source.

### Extract from a Subversion URL

The next example demonstrates how to extract from a Subversion repository URL:

Extract configuration example 2 - extract from a Subversion URL
    cfg::type           ext                    # line 1
    cfg::version        1.0                    # line 2
                                               # line 3
    dest::rootdir       $PWD                   # line 4
                                               # line 5
    repos::var::trunk   svn://server/var/trunk # line 6
    version::var::trunk 1234                   # line 7
                                               # line 8
    expsrc::var::trunk  code                   # line 9

- line 1 to 5: same as example 1.
- line 6: the line declares the repository location of the "trunk" branch of the "var" package to be the Subversion URL "svn://server/var/trunk".
- line 7: the label "VERSION::<pck>::<branch>" declares the revision of the repository associated with the package <pck> in the branch <branch>. The current line tells the extract system to use revision 1234 of "svn://server/var/trunk". If the revision is not declared, the default revision "HEAD" will be assumed.
- line 8: comment line, ignored.
- line 9: the line declares an expandable source directory in the repository "svn://server/var/trunk".

Invoking the extract system using the above configuration file will extract all sub-directories under "svn://server/var/trunk/code" to "$PWD/src/var/code". It will write a build configuration file to "$PWD/cfg/bld.cfg". The configuration used for this extraction will be written to the configuration file at "$PWD/cfg/ext.cfg".

Note - declaration of source directories for extraction
EXPSRC or SRC? So far, we have only declared source directories using the "EXPSRC" statement, which stands for "expandable source directory". A source directory declared using this statement will trigger the system to search recursively for any sub-directories under the declared one. Any sub-directories containing regular source files will be included in the extraction. Empty directories, hidden directories and directories containing only hidden files are ignored. If you do not want the system to search for sub-directories underneath your declared source directory, you can declare your source directory using the "SRC" statement. The "SRC" statement is essentially the same as "EXPSRC" except that it does not trigger the automatic recursive search for source directories. In fact, the system implements the "EXPSRC" statement by expanding it into a list of "SRC" statements. Package and sub-package The second field of a repository, revision or source directory declaration label is the name of the container package. It is a name selected by the user to identify the system or project he/she is working on. (Therefore, it is often sensible to choose an identifier that matches the name of the project or system.) The package name provides a unique namespace for a file container. Source directories are automatically arranged into sub-packages, using the names of the sub-directories as the names of the sub-packages. For example, the declaration at line 9 in example 2 will put the source directory in the "var::code" sub-package automatically. The double colon "::" and the double underscore "__" (internal only) are delimiters for package names in the extract system. Please avoid using "::" and "__" for naming your files and directories. You can declare a sub-package name explicitly in your source directory statement. For example, the following two lines are equivalent:
    src::var::trunk                        code/VarMod_Surface
    src::var::code::VarMod_Surface::trunk  code/VarMod_Surface
Explicit sub-package declaration should not be used normally, as it requires a lot more typing (although there are some situations where it can be useful).

Note - the expanded extract configuration file
At the end of a successful extraction, the configuration used by the current extraction is written in "cfg/ext.cfg" under the extract destination root. This file is an "expanded" version of the original, with changes in the following declarations: All revision keywords are converted into revision numbers. If a revision is not defined for a repository, it is set to the corresponding revision number of the HEAD revision. All URL keywords are converted into the full URLs. All EXPSRC declarations are expanded into SRC declarations. All other variables are expanded. With this file, it should be possible for later extraction to re-create the current configuration even if the contents of the repository have changed. (This applies only to code stored in the repository.)

### Mirror code to a remote machine

The next example demonstrates how to extract from a repository and mirror the code to a remote machine. It is essentially the same as example 2, except that it has three new lines to describe how the system can mirror the extracted code to a remote machine.

Extract configuration example 3 - mirror code to remote machine
    cfg::type           ext
    cfg::version        1.0

    dest::rootdir       $PWD

    rdest::machine      tx01                           # line 6
    rdest::logname      frva                           # line 7
    rdest::rootdir      /scratch/frva/extract/example3 # line 8

    repos::var::trunk   svn://server/var/trunk
    version::var::trunk 1234

    expsrc::var::trunk  code

Here is an explanation of what each line does:

- line 6: "RDEST::MACHINE" declares the target machine to which the code will be mirrored. The example mirrors the code to the machine named "tx01".
- line 7: "RDEST::LOGNAME" declares the remote user name of the target machine, to which the user has remote login access. If this is not declared, the system uses the login name of the current user on the local machine.
- line 8: "RDEST::ROOTDIR" declares the root directory of the extraction on the remote target machine. This is where the mirror version of the extraction will be sent.

Invoking the extract system on the above configuration will trigger an extraction similar to that given in example 2, but it will also attempt to mirror the contents at "$PWD/src/var/code" to "/scratch/frva/extract/example3/src" on the remote machine. It will also mirror the expanded extract configuration file "$PWD/cfg/ext.cfg" to "/scratch/frva/extract/example3/cfg/ext.cfg" and "$PWD/cfg/bld.cfg" to "/scratch/frva/extract/example3/cfg/bld.cfg". It is also worth noting that the content of the build configuration file will be slightly different, since it will include directory names appropriate for the remote system.

Note - mirroring command
The extract system currently supports "rdist" and "rsync" as its mirroring tool. The default is "rsync". To use "rdist" instead of "rsync", add the following line to your "$HOME/.fcm" file:
    set::tool::mirror  rdist
N.B. If you are going to mirror code to another machine, you need to ensure that your account on the remote machine is set up correctly to accept commands from the local machine. In our current settings of both "rdist" and "rsync", all you need to do is set up your "$HOME/.rhosts" file on the remote machine. For example, if you are "fred" working on the local machine "eld001", you will need to have the following entry in your "$HOME/.rhosts" on the remote machine:
    eld001  fred

## Advanced Usage

### Extract from multiple repositories

So far, we have only extracted from a single location. The extract system is not much use if that is the only thing it can do. In fact, the extract system supports extraction of multiple source directories from multiple branches in multiple repositories. The following configuration file is an example of how to extract from multiple repositories:

Extract configuration example 4 - extract from multiple repositories
    cfg::type           ext
    cfg::version        1.0

    dest::rootdir       $PWD

    repos::var::trunk   fcm:var_tr              # line 6
    repos::ops::trunk   fcm:ops_tr              # line 7
    repos::gen::trunk   fcm:gen_tr              # line 8

    version::gen::trunk 2468                    # line 10

    expsrc::var::trunk  code                    # line 12
    expsrc::var::trunk  scripts                 # line 13
    expsrc::ops::trunk  code                    # line 14
    src::gen::trunk     code/GenMod_Constants   # line 15
    src::gen::trunk     code/GenMod_Control     # line 16
    src::gen::trunk     code/GenMod_FortranIO   # line 17
    src::gen::trunk     code/GenMod_GetEnv      # line 18
    src::gen::trunk     code/GenMod_ModelIO     # line 19
    src::gen::trunk     code/GenMod_ObsInfo     # line 20
    src::gen::trunk     code/GenMod_Platform    # line 21
    src::gen::trunk     code/GenMod_Reporting   # line 22
    src::gen::trunk     code/GenMod_Trace       # line 23
    src::gen::trunk     code/GenMod_UMConstants # line 24
    src::gen::trunk     code/GenMod_Utilities   # line 25

Here is an explanation of what each line does:

- line 6 to 8: these lines declare the repositories for the "trunk" branches of the "var", "ops" and "gen" packages respectively. It is worth noting that the values of the declarations are no longer Subversion URLs but are FCM URL keywords. These keywords are normally declared in the central configuration file of the FCM system, and will be expanded into the corresponding Subversion URLs by the FCM system. For further information on URL keywords, please see Code Management System > Using Subversion > Basic Command Line Usage > Repository & Revision Keywords.
- line 10: this line declares the revision number for the "trunk" branch of the "gen" package, i.e. for the "fcm:gen_tr" repository. It is worth noting that the revision numbers for the "var" and "ops" packages have not been declared. By default, their revision numbers will be set to "HEAD".
- line 12 to 14: these line declares the source directories for the "trunk" branches of the "var" and "ops" packages. For the "var" package, we are extracting everything from the "code" and the "scripts" sub-directory. For the "ops" package, we are extracting everything from the "code" directory.
- line 15 to 25: these line declares the source directories for the "trunk" branch of the "gen" package. The source directories declared will not be searched for sub-directories underneath the declared directories.

We shall end up with a directory tree such as:

    $PWD
       |
       |--- cfg
       |      |
       |      |--- bld.cfg
       |      |--- ext.cfg
       |
       |--- src
              |
              |--- gen
              |      |
              |      |--- code
              |              |
              |              |--- GenMod_Constants
              |              |--- GenMod_Control
              |              |--- GenMod_FortranIO
              |              |--- GenMod_GetEnv
              |              |--- GenMod_ModelIO
              |              |--- GenMod_ObsInfo
              |              |--- GenMod_Platform
              |              |--- GenMod_Reporting
              |              |--- GenMod_Trace
              |              |--- GenMod_UMConstants
              |              |--- GenMod_Utilities
              |
              |--- ops
              |      |
              |      |--- code
              |              |
              |              |--- ...
              |
              |--- var
                     |
                     |--- code
                     |       |
                     |       |--- ...
                     |
                     |--- scripts
                             |
                             |--- ...

Note - revision number
As seen in the above example, if a revision number is not specified for a repository URL, it defaults to the "HEAD" revision. The revision number can also be declared in other ways: Any revision arguments acceptable by Subversion are allowed. You can use a valid revision number, a date between a pair of curly brackets (e.g. {"2005-05-01 12:00"}) or the keyword "HEAD". However, please do not use the keywords "BASE", "COMMITTED" or "PREV" as these are reserved for working copy only. FCM revision keywords are allowed. These must be defined for the corresponding repository URLs in either the central or the user FCM configuration file. For further information on revision keywords, please see Code Management > Using Subversion > Basic Command Line Usage > Repository & Revision Keywords. Do not use the keyword "USER", as it is used internally by the extract system.

### Extract from multiple branches

We have so far dealt with extraction from a single branch in any package. The extract system can be used to "combine" changes from different branches of a package. An example is given below:

Extract configuration example 5 - extract from multiple branches
    cfg::type               ext
    cfg::version            1.0

    dest::rootdir           $PWD

    repos::var::trunk       fcm:var_tr
    repos::ops::trunk       fcm:ops_tr
    repos::gen::trunk       fcm:gen_tr

    version::gen::trunk     2468

    expsrc::var::trunk      code
    expsrc::var::trunk      scripts
    expsrc::ops::trunk      code
    src::gen::trunk         code/GenMod_Constants
    src::gen::trunk         code/GenMod_Control
    src::gen::trunk         code/GenMod_FortranIO
    src::gen::trunk         code/GenMod_GetEnv
    src::gen::trunk         code/GenMod_ModelIO
    src::gen::trunk         code/GenMod_ObsInfo
    src::gen::trunk         code/GenMod_Platform
    src::gen::trunk         code/GenMod_Reporting
    src::gen::trunk         code/GenMod_Trace
    src::gen::trunk         code/GenMod_UMConstants
    src::gen::trunk         code/GenMod_Utilities

    repos::var::new_stuff   fcm:var_br/frva/r1234_new_stuff   # line 27
    repos::var::bug_fix     fcm:var_br/frva/r1516_bug_fix     # line 28
    repos::ops::good_stuff  fcm:ops_br/opsrc/r3188_good_stuff # line 29

The configuration file in example 5 is similar to that of example 4 except for the last three lines. Here is an explanation of what they do:

- line 27: this line declares a repository URL for the "new_stuff" branch of the "var" package. From the URL of the branch, we know that the branch was created by the user "frva" based on the trunk at revision at 1234. The description of the branch is "new_stuff". The following points are worth noting:
  - By declaring a new branch with the same package name to a previously declared branch, it is assumed that both branches reside in the same Subversion repository.
  - It is only by convention that the branch name "new_stuff" declared using the "REPOS::var::new_stuff" label should correspond to the branch description of the URL. It is not a requirement by the extract system. It is perfectly valid to use "REPOS::var::ham_egg" as the label of line 27. In such case, the extract system will use "ham_egg" instead of "new_stuff" as the internal label of the URL.
  - No revision is declared for this URL, so the default "HEAD" revision is used.
  - No source directory is declared for this URL. By default, if no source directory is declared for a branch repository, it will attempt to use the same set of source directories as the first declared branch of the package. In this case, the source directories declared for the "trunk" branch of the "var" package will be used.
- line 28: this line declares another branch called "bug_fix" for the "var" package. No source directory is declared for this URL either, so it will use the same set of source directories declared for the "trunk" branch.
- line 29: this line declares a branch called "good_stuff" for the "ops" package. It will use the same set of source directories declared for the "ops" package "trunk" branch.

When we invoke the extract system, it will attempt to extract from the first declared branch of a package, if the last commit revision of the source directory is the same in all the branches. However, if the last commit revision of the source directory differs for different branches, the system will attempt to obtain an extract priority list for each source directory, using the following logic:

1. The system looks for source directory packages from the first declared branch to the last declared branch.
2. The branch in which a source directory package is first declared is the "base" branch of the source directory package.
3. The commit revision of a source directory package in a subsequently declared repository branch is compared with that of the base branch. If the commit revision is the same as that of the base branch, the source directory of this branch is discarded. Otherwise, it is placed at the end of the extract priority list.

For the "var" package in the above example, let us assume that we have three source directory packages X, Y and Z under "code", and their commit revisions under "trunk" are 100. Let's say we have committed some changes to X and Z in the "new_stuff" branch at revision 102, and other changes to Y and Z in the "bug_fix" branch at revision 104, the extract priority lists for X, Y and Z will look like:

- X: trunk (100, base), new_stuff (102), bug_fix (100, discarded)
- Y: trunk (100, base), new_stuff (100, discarded), bug_fix (104)
- Z: trunk (100, base), new_stuff (102), bug_fix (104)

Once we have an extract priority list for a source directory, we can begin the extraction of source files in the source directory. The source directory of the base branch is extracted first, followed by that in the subsequent branches. If a source file in a subsequent branch has the same content as the that in the base branch, it is discarded. Otherwise, the following logic determines the branch to use:

1. If a source file is modified in only one subsequent branch, the source file in that branch is extracted.
2. If a source file is modified in two or more subsequent branches, but their modifications are the same, then the source file in the first modification is used.
3. If a source file is modified in two or more subsequent branches and their modifications differ, then the behaviour depends on the override mode setting. If override mode is false, the extraction fails. Otherwise, the file in the latest declared branch takes precedence. The default override mode is false, which is the safe behaviour - conflicting changes should be resolved manually. However, this behaviour may not be the most efficient way for development. Therefore, an override mode is provided, which should be used with care. To switch on the override mode, make the following declaration in the extract configuration file:

       override  1

Once the system has established which source files to use, it determines whether the destination is out of date or not. The destination is out of date if the source file does not exist or if its content differs from the version of the source file we are using. The system only updates the destination if it is considered to be out of date.

The extract system can also combine changes from branches in the Subversion repository and the local file system. The limitation is that there can only be one branch from the local file system. (By convention, the branch is named "user".)

It is also worth bearing in mind that the "user" branch always takes precedence over branches residing in Subversion repositories. Hence, source directories from a "user" branch are always placed at the end of the extract priority list.

Extracting from a mixture of Subversion repository and local file system is demonstrated in the next example.

Extract configuration example 6 - extract from multiple branches + user paths
    cfg::type               ext
    cfg::version            1.0

    dest::rootdir           $PWD

    repos::var::trunk       fcm:var_tr
    repos::ops::trunk       fcm:ops_tr
    repos::gen::trunk       fcm:gen_tr

    version::gen::trunk     2468

    expsrc::var::trunk      code
    expsrc::var::trunk      scripts
    expsrc::ops::trunk      code
    src::gen::trunk         code/GenMod_Constants
    src::gen::trunk         code/GenMod_Control
    src::gen::trunk         code/GenMod_FortranIO
    src::gen::trunk         code/GenMod_GetEnv
    src::gen::trunk         code/GenMod_ModelIO
    src::gen::trunk         code/GenMod_ObsInfo
    src::gen::trunk         code/GenMod_Platform
    src::gen::trunk         code/GenMod_Reporting
    src::gen::trunk         code/GenMod_Trace
    src::gen::trunk         code/GenMod_UMConstants
    src::gen::trunk         code/GenMod_Utilities

    repos::var::new_stuff   fcm:var_br/frva/r1234_new_stuff
    repos::var::bug_fix     fcm:var_br/frva/r1516_bug_fix
    repos::ops::good_stuff  fcm:ops_br/opsrc/r3188_good_stuff

    repos::var::user        $HOME/var/src                     # line 31
    repos::gen::user        $HOME/gen/src                     # line 32

Example 6 is similar to example 5 except that it is also extracting from local directories. Here is an explanation of the lines:

- line 31 to 32: these line declare the "repositories" for the "user" branches of the "var" and "gen" packages respectively. Both are local paths at the local file system. There are no declarations for source directories for the "user" branches, so they use the same set of source directories of the first declared branches, the "trunk" branches in both cases.

Note - the INC declaration
You have probably realised that the above examples have many repeated lines. To avoid having repeated lines in multiple extract configuration files, you can use INC declarations to "include" other extract configuration files. For example, if the configuration file of example 5 is stored in the file "$HOME/var/example5/ext.cfg", line 1 to 29 of example 6 can be replaced with an INC declaration. Example 6 can then be written as:
    inc                     $HOME/var/example5/ext.cfg

    repos::var::user        $HOME/var/src
    repos::gen::user        $HOME/gen/src
Note: the INC declaration supports the special "environment variable" $HERE. If this variable is already set in the environment, it acts as a normal environment variable. However, if it is not set, it will be expanded into the container directory of the current extract configuration file. This feature is particularly useful if you are including a hierarchy of extract configurations from files in the same container directory in a repository.

### Incremental extract based on a previous extraction

All the examples above dealt with standalone extraction, that is, the current extraction is independent of any other extraction. If a previous extraction exists in another location, the extract system can "USE" this previous extraction in your current extraction. This works like a normal incremental extraction, except that your extraction will only contain the changes you have specified (compared with the USEd extraction) instead of the full source directory tree. This type of incremental extraction is useful in several ways. For instance:

- The extraction is fast, because you only have to extract and mirror files that you have changed.
- The subsequent build will also be fast, since it will use incremental build.
- You do not need write access to the original extraction. A system administrator can set up a stable version in a central account, which developers can then reuse.
- You want an incremental extraction, but you need to leave the original extraction unmodified.

The following example is based on example 4 and 6. The assumption is that an extraction has already been performed at the directory "~frva/var/vn22.0" based on the configuration file in example 4.

Extract configuration example 7 - incremental extract based on a previous extraction
    cfg::type               ext
    cfg::version            1.0

    dest::rootdir           $PWD

    use                     ~frva/var/vn22.0                  # line 6

    repos::var::new_stuff   fcm:var_br/frva/r1234_new_stuff   # line 8
    repos::var::bug_fix     fcm:var_br/frva/r1516_bug_fix     # line 9
    repos::ops::good_stuff  fcm:ops_br/opsrc/r3188_good_stuff # line 10

    repos::var::user        $HOME/var/src                     # line 12
    repos::gen::user        $HOME/gen/src                     # line 13

- line 6: this line replaces line 1 to 25 of example 6. It declares that the current extraction should be based on the previous extraction located at "~frva/var/vn22.0".

Running the extract system using the above configuration will trigger an incremental extraction, as if you are running an incremental extraction having modified the configuration file in example 4 to that of example 6. The only difference is that the original extraction using the example 4 configuration will be left untouched at "~frva/var/vn22.0", and the new extraction will contain only the changes in the branches declared from line 8 to 13.

If you are setting up an extraction to be reused, you do not have to perform a build. If you don't you will still gain the benefit of incremental file extraction, but you will be performing a full build of the code.

### Extract - Build Configuration

Configuration settings for feeding into the build system can be declared through the extract configuration file using the "BLD::" prefix. Any line in an extract configuration containing a label with such a prefix will be considered a build system variable. At the end of a successful extraction, the system strips out the "BLD::" prefix before writing these variables to the build configuration file. Some example entries are given between line 17 and 22 in the following configuration file:

Extract configuration example 8 - setting build configuration
    cfg::type           ext
    cfg::version        1.0

    dest::rootdir       $PWD

    repos::var::trunk   fcm:var_tr
    repos::ops::trunk   fcm:ops_tr
    repos::gen::trunk   fcm:gen_tr

    version::gen::trunk 2468

    expsrc::var::trunk  code
    expsrc::var::trunk  scripts
    expsrc::ops::trunk  code
    src::gen::trunk     code/GenMod_Constants
    src::gen::trunk     code/GenMod_Control
    src::gen::trunk     code/GenMod_FortranIO
    src::gen::trunk     code/GenMod_GetEnv
    src::gen::trunk     code/GenMod_ModelIO
    src::gen::trunk     code/GenMod_ObsInfo
    src::gen::trunk     code/GenMod_Platform
    src::gen::trunk     code/GenMod_Reporting
    src::gen::trunk     code/GenMod_Trace
    src::gen::trunk     code/GenMod_UMConstants
    src::gen::trunk     code/GenMod_Utilities

    bld::target         VarProg_AnalysePF.exe   # line 27

    bld::tool::fc       sxmpif90                # line 29
    bld::tool::cc       sxmpic++                # line 30
    bld::tool::ld       sxmpif90                # line 31

The above example is essentially the same as example 4, apart from the additional build configuration. The following is a simple explanation of what the lines represent: (For detail of the build system, please see the next chapter on The Build System.)

- Line 27: the line declares a default target of the build.
- Line 29-31: the lines declare the Fortran compiler, the C compiler and the linker respectively.

Note - user variable
When you start using the extract system to define compiler flags for the build system, you may end up having to make a lot of long and repetitive declarations. In such case, you may want to define variables to replace the repetitive parts of the declarations. In the extract system, you can define a local variable by making a declaration with a label that begins with a percent sign "%". For example:
    # Declare a variable %fred
    %fred                     -Cdebug -eC -Wf,-init heap=nan stack=nan

    bld::tool::fflags         %fred
    # bld::tool::fflags       -Cdebug -eC -Wf,-init heap=nan stack=nan

    bld::tool::fflags::foo    %fred -f0
    # bld::tool::fflags::foo  -Cdebug -eC -Wf,-init heap=nan stack=nan -f0

    bld::tool::fflags::bar    -w %fred
    # bld::tool::fflags::bar  -w -Cdebug -eC -Wf,-init heap=nan stack=nan

## Diagnostic verbose level

The amount of diagnostic messages generated by the extract system is normally set to a level suitable for normal everyday operation. This is the default diagnostic verbose level 1. If you want a minimum amount of diagnostic messages, you should set the verbose level to 0. If you want more diagnostic messages, you can set the verbose level to 2 or 3. You can modify the verbose level in two ways. The first way is to set the environment variable FCM_VERBOSE to the desired verbose level. The second way is to invoke the extract system with the "-v <level>" option. (If set, the command line option overrides the environment variable.)

The following is a list of diagnostic output at each verbose level:

Verbose level | Possible output
--- | ---
0 | Report the time taken to extract the code. Report the time taken to mirror the code. If "rdist" is used to mirror the code, run the command with the "-q" option.
1 | Everything at verbose level 0. Report the name of the extract configuration file. Report date/time at the beginning of the extract step. Report the number of directories created, number of ignored sub-directories, number of files updated and number of removed files. In override mode, report any files that are modified in two or more branches. Report date/time at the beginning of the mirror step. Report total time.
2 | Everything at verbose level 1. If the revision specified for a repository branch is not current (i.e. the specified revision number is less than the revision number of the last commit revision), print an information statement to inform the user of the last commit revision of the branch. Report details of created directories, ignored sub-directories, removed files and updated files. Report any files that have the same modifications in two or more branches. If "rdist" is used to mirror the code, run the command without the "-q" option.
3 | Everything at verbose level 2. Report all shell commands invoked by the extract system with timestamp. If "rdist" is used to mirror the code, print the "distfile" supplied to the command. If "rsync" is used to mirror the code, invoke the command with the "-v" option.

## When Subversion Is Not Available

The extract system can still be used if Subversion is not available. Clearly, you can only use local repositories. However, you can still do incremental extraction, mirror an extraction to another machine, or combine code from multiple local repositories.

If you are using Subversion but your server is down then clearly there is little you can do. However, if you already have an extraction then you can re-run `fcm extract` as long as the extract configuration file only refers to fixed revisions. If this is not the case then you can always use the expanded extract configuration file which can be found in "cfg/ext.cfg" under the extract destination root. This means that you can continue to makes changes to local code and do incremental extractions even whilst your Subversion server is down.