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% Cabal User Guide

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# Configuration #

## Overview ##

The global configuration file for `cabal-install` is `~/.cabal/config`. If you
do not have this file, `cabal` will create it for you on the first call to
`cabal update`. Alternatively, you can explicitly ask `cabal` to create it for
you using

> `cabal user-config update`

Most of the options in this configuration file are also available as command
line arguments, and the corresponding documentation can be used to lookup their
meaning. The created configuration file only specifies values for a handful of
options. Most options are left at their default value, which it documents;
for instance,

~~~~~~~~~~~~~~~~
-- executable-stripping: True
~~~~~~~~~~~~~~~~

means that the configuration file currently does not specify a value for the
`executable-stripping` option (the line is commented out), and that the default
is `True`; if you wanted to disable stripping of executables by default, you
would change this line to

~~~~~~~~~~~~~~~~
executable-stripping: False
~~~~~~~~~~~~~~~~

You can also use `cabal user-config update` to migrate configuration files
created by older versions of `cabal`.

## Repository specification ##

An important part of the configuration if the specification of the repository.
When `cabal` creates a default config file, it configures the repository to
be the central Hackage server:

~~~~~~~~~~~~~~~~
repository hackage.haskell.org
  url: http://hackage.haskell.org/
~~~~~~~~~~~~~~~~

The name of the repository is given on the first line, and can be anything;
packages downloaded from this repository will be cached under
`~/.cabal/packages/hackage.haskell.org` (or whatever name you specify; you can
change the prefix by changing the value of `remote-repo-cache`). If you want,
you can configure multiple repositories, and `cabal` will combine them and be
able to download packages from any of them.

### Using secure repositories ###

For repositories that support the TUF security infrastructure (this includes
Hackage), you can enable secure access to the repository by specifying:

~~~~~~~~~~~~~~~~
repository hackage.haskell.org
  url: http://hackage.haskell.org/
  secure: True
  root-keys: <root-key-IDs>
  key-threshold: <key-threshold>
~~~~~~~~~~~~~~~~

The `<root-key-IDs>` and `<key-threshold>` values are used for bootstrapping. As
part of the TUF infrastructure the repository will contain a file `root.json`
(for instance,
[http://hackage.haskell.org/root.json](http://hackage.haskell.org/root.json))
which the client needs to do verification. However, how  can `cabal` verify the
`root.json` file _itself_? This is known as bootstrapping: if you specify a list
of root key IDs and a corresponding  threshold, `cabal` will verify that the
downloaded `root.json` file has been  signed with at least `<key-threshold>`
keys from your set of `<root-key-IDs>`.

You can, but are not recommended to, omit these two fields. In that case `cabal`
will download the `root.json` field and use it without verification. Although
this bootstrapping step is then unsafe, all subsequent access is secure
(provided that the downloaded `root.json` was not tempered with). Of course,
adding `root-keys` and `key-threshold` to your repository specification only
shifts the problem, because now you somehow need to make sure that the key IDs
you received were the right ones. How that is done is however outside the scope
of `cabal` proper.

More information about the security infrastructure can be found at
[https://github.com/well-typed/hackage-security](https://github.com/well-typed/hackage-security).

### Legacy repositories ###

Currently `cabal` supports two kinds of &ldquo;legacy&rdquo; repositories. The
first is specified using

~~~~~~~~~~~~~~~~
remote-repo: hackage.haskell.org:http://hackage.haskell.org/packages/archive
~~~~~~~~~~~~~~~~

This is just syntactic sugar for

~~~~~~~~~~~~~~~~
repository hackage.haskell.org
  url: hackage.haskell.org:http://hackage.haskell.org/packages/archive
~~~~~~~~~~~~~~~~

although, in (and only in) the specific case of Hackage, the URL
`http://hackage.haskell.org/packages/archive` will be silently translated to
`http://hackage.haskell.org/`.

The second kind of legacy repositories are so-called &ldquo;local&rdquo;
repositories:

~~~~~~~~~~~~~~~~
local-repo: my-local-repo:/path/to/local/repo
~~~~~~~~~~~~~~~~

This can be used to access repositories on the local file system. However, the
layout of these local repositories is different from the layout of remote
repositories, and usage of these local repositories is deprecated.

### Secure local repositories ###

If you want to use repositories on your local file system, it is recommended
instead to use a _secure_ local repository:

~~~~~~~~~~~~~~~~
repository my-local-repo
  url: file:/path/to/local/repo
  secure: True
  root-keys: <root-key-IDs>
  key-threshold: <key-threshold>
~~~~~~~~~~~~~~~~

The layout of these secure local repos matches the layout of remote repositories
exactly; the
[hackage-repo-tool](http://hackage.haskell.org/package/hackage-repo-tool) can be
used to create and manage such repositories.

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# Building and installing packages #

After you've unpacked a Cabal package, you can build it by moving into
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the root directory of the package and running the `cabal` tool there:

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> `cabal [command] [option...]`
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The _command_ argument selects a particular step in the build/install process.

You can also get a summary of the command syntax with

> `cabal help`

Alternatively, you can also use the `Setup.hs` or `Setup.lhs` script:
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> `runhaskell Setup.hs [command] [option...]`
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For the summary of the command syntax, run:
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> `cabal help`

or

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> `runhaskell Setup.hs --help`

## Building and installing a system package ##

~~~~~~~~~~~~~~~~
runhaskell Setup.hs configure --ghc
runhaskell Setup.hs build
runhaskell Setup.hs install
~~~~~~~~~~~~~~~~

The first line readies the system to build the tool using GHC; for
example, it checks that GHC exists on the system.  The second line
performs the actual building, while the last both copies the build
results to some permanent place and registers the package with GHC.

## Building and installing a user package ##

~~~~~~~~~~~~~~~~
runhaskell Setup.hs configure --user
runhaskell Setup.hs build
runhaskell Setup.hs install
~~~~~~~~~~~~~~~~

The package is installed under the user's home directory and is
registered in the user's package database (`--user`).

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## Installing packages from Hackage ##

The `cabal` tool also can download, configure, build and install a [Hackage]
package and all of its dependencies in a single step. To do this, run:

~~~~~~~~~~~~~~~~
cabal install [PACKAGE...]
~~~~~~~~~~~~~~~~

To browse the list of available packages, visit the [Hackage] web site.

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## Developing with sandboxes ##

By default, any dependencies of the package are installed into the global or
user package databases (e.g. using `cabal install --only-dependencies`). If
you're building several different packages that have incompatible dependencies,
this can cause the build to fail. One way to avoid this problem is to build each
package in an isolated environment ("sandbox"), with a sandbox-local package
database. Because sandboxes are per-project, inconsistent dependencies can be
simply disallowed.

For more on sandboxes, see also
[this article](http://coldwa.st/e/blog/2013-08-20-Cabal-sandbox.html).

### Sandboxes: basic usage ###

To initialise a fresh sandbox in the current directory, run `cabal sandbox
init`. All subsequent commands (such as `build` and `install`) from this point
will use the sandbox.

~~~~~~~~~~~~~~~
$ cd /path/to/my/haskell/library
$ cabal sandbox init                   # Initialise the sandbox
$ cabal install --only-dependencies    # Install dependencies into the sandbox
$ cabal build                          # Build your package inside the sandbox
~~~~~~~~~~~~~~~

It can be useful to make a source package available for installation in the
sandbox - for example, if your package depends on a patched or an unreleased
version of a library. This can be done with the `cabal sandbox add-source`
command - think of it as "local [Hackage]". If an add-source dependency is later
modified, it is reinstalled automatically.

~~~~~~~~~~~~~~~
$ cabal sandbox add-source /my/patched/library # Add a new add-source dependency
$ cabal install --dependencies-only            # Install it into the sandbox
$ cabal build                                  # Build the local package
$ $EDITOR /my/patched/library/Source.hs        # Modify the add-source dependency
$ cabal build                                  # Modified dependency is automatically reinstalled
~~~~~~~~~~~~~~~

Normally, the sandbox settings (such as optimisation level) are inherited from
the main Cabal config file (`$HOME/cabal/config`). Sometimes, though, you need
to change some settings specifically for a single sandbox. You can do this by
creating a `cabal.config` file in the same directory with your
`cabal.sandbox.config` (which was created by `sandbox init`). This file has the
same syntax as the main Cabal config file.

~~~~~~~~~~~~~~~
$ cat cabal.config
documentation: True
constraints: foo == 1.0, bar >= 2.0, baz
$ cabal build                                  # Uses settings from the cabal.config file
~~~~~~~~~~~~~~~

When you have decided that you no longer want to build your package inside a
sandbox, just delete it:

~~~~~~~~~~~~~~~
$ cabal sandbox delete                       # Built-in command
$ rm -rf .cabal-sandbox cabal.sandbox.config # Alternative manual method
~~~~~~~~~~~~~~~

### Sandboxes: advanced usage ###

The default behaviour of the `add-source` command is to track modifications done
to the added dependency and reinstall the sandbox copy of the package when
needed. Sometimes this is not desirable: in these cases you can use `add-source
--snapshot`, which disables the change tracking. In addition to `add-source`,
there are also `list-sources` and `delete-source` commands.

Sometimes one wants to share a single sandbox between multiple packages. This
can be easily done with the `--sandbox` option:

~~~~~~~~~~~~~~~
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$ mkdir -p /path/to/shared-sandbox
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$ cd /path/to/shared-sandbox
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$ cabal sandbox init --sandbox .
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$ cd /path/to/package-a
$ cabal sandbox init --sandbox /path/to/shared-sandbox
$ cd /path/to/package-b
$ cabal sandbox init --sandbox /path/to/shared-sandbox
~~~~~~~~~~~~~~~

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Note that `cabal sandbox init --sandbox .` puts all sandbox files into the
current directory. By default, `cabal sandbox init` initialises a new sandbox in
a newly-created subdirectory of the current working directory
(`./.cabal-sandbox`).

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Using multiple different compiler versions simultaneously is also supported, via
the `-w` option:

~~~~~~~~~~~~~~~
$ cabal sandbox init
$ cabal install --only-dependencies -w /path/to/ghc-1 # Install dependencies for both compilers
$ cabal install --only-dependencies -w /path/to/ghc-2
$ cabal configure -w /path/to/ghc-1                   # Build with the first compiler
$ cabal build
$ cabal configure -w /path/to/ghc-2                   # Build with the second compiler
$ cabal build
~~~~~~~~~~~~~~~

It can be occasionally useful to run the compiler-specific package manager tool
(e.g. `ghc-pkg`) tool on the sandbox package DB directly (for example, you may
need to unregister some packages). The `cabal sandbox hc-pkg` command is a
convenient wrapper that runs the compiler-specific package manager tool with the
arguments:

~~~~~~~~~~~~~~~
$ cabal -v sandbox hc-pkg list
Using a sandbox located at /path/to/.cabal-sandbox
'ghc-pkg' '--global' '--no-user-package-conf'
    '--package-conf=/path/to/.cabal-sandbox/i386-linux-ghc-7.4.2-packages.conf.d'
    'list'
[...]
~~~~~~~~~~~~~~~

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The `--require-sandbox` option makes all sandbox-aware commands
(`install`/`build`/etc.) exit with error if there is no sandbox present. This
makes it harder to accidentally modify the user package database. The option can
be also turned on via the per-user configuration file (`~/.cabal/config`) or the
per-project one (`$PROJECT_DIR/cabal.config`). The error can be squelched with
`--no-require-sandbox`.

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The option `--sandbox-config-file` allows to specify the location of the
`cabal.sandbox.config` file (by default, `cabal` searches for it in the current
directory). This provides the same functionality as shared sandboxes, but
sometimes can be more convenient. Example:

~~~~~~~~~~~~~~~
$ mkdir my/sandbox
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$ cd my/sandbox
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$ cabal sandbox init
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$ cd /path/to/my/project
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$ cabal --sandbox-config-file=/path/to/my/sandbox/cabal.sandbox.config install
# Uses the sandbox located at /path/to/my/sandbox/.cabal-sandbox
$ cd ~
$ cabal --sandbox-config-file=/path/to/my/sandbox/cabal.sandbox.config install
# Still uses the same sandbox
~~~~~~~~~~~~~~~

The sandbox config file can be also specified via the `CABAL_SANDBOX_CONFIG`
environment variable.

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Finally, the flag `--ignore-sandbox` lets you temporarily ignore an existing
sandbox:

~~~~~~~~~~~~~~~
$ mkdir my/sandbox
$ cd my/sandbox
$ cabal sandbox init
$ cabal --ignore-sandbox install text
# Installs 'text' in the user package database ('~/.cabal').
~~~~~~~~~~~~~~~

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## Creating a binary package ##

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When creating binary packages (e.g. for Red Hat or Debian) one needs to
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create a tarball that can be sent to another system for unpacking in the
root directory:

~~~~~~~~~~~~~~~~
runhaskell Setup.hs configure --prefix=/usr
runhaskell Setup.hs build
runhaskell Setup.hs copy --destdir=/tmp/mypkg
tar -czf mypkg.tar.gz /tmp/mypkg/
~~~~~~~~~~~~~~~~

If the package contains a library, you need two additional steps:

~~~~~~~~~~~~~~~~
runhaskell Setup.hs register --gen-script
runhaskell Setup.hs unregister --gen-script
~~~~~~~~~~~~~~~~

This creates shell scripts `register.sh` and `unregister.sh`, which must
also be sent to the target system.  After unpacking there, the package
must be registered by running the `register.sh` script. The
`unregister.sh` script would be used in the uninstall procedure of the
package. Similar steps may be used for creating binary packages for
Windows.


The following options are understood by all commands:

`--help`, `-h` or `-?`
:   List the available options for the command.

`--verbose=`_n_ or `-v`_n_
:   Set the verbosity level (0-3). The normal level is 1; a missing _n_
    defaults to 2.

The various commands and the additional options they support are
described below. In the simple build infrastructure, any other options
will be reported as errors.

## setup configure ##

Prepare to build the package.  Typically, this step checks that the
target platform is capable of building the package, and discovers
platform-specific features that are needed during the build.

The user may also adjust the behaviour of later stages using the options
listed in the following subsections.  In the simple build
infrastructure, the values supplied via these options are recorded in a
private file read by later stages.

If a user-supplied `configure` script is run (see the section on
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[system-dependent
parameters](developing-packages.html#system-dependent-parameters) or on
[complex packages](developing-packages.html#more-complex-packages)), it
is passed the `--with-hc-pkg`, `--prefix`, `--bindir`, `--libdir`,
`--datadir`, `--libexecdir` and `--sysconfdir` options. In addition the
value of the `--with-compiler` option is passed in a `--with-hc` option
and all options specified with `--configure-option=` are passed on.
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### Programs used for building ###

The following options govern the programs used to process the source
files of a package:

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`--ghc` or `-g`, `--jhc`, `--lhc`, `--uhc`
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:   Specify which Haskell implementation to use to build the package.
    At most one of these flags may be given. If none is given, the
    implementation under which the setup script was compiled or
    interpreted is used.

`--with-compiler=`_path_ or `-w`_path_
:   Specify the path to a particular compiler. If given, this must match
    the implementation selected above. The default is to search for the
    usual name of the selected implementation.

    This flag also sets the default value of the `--with-hc-pkg` option
    to the package tool for this compiler. Check the output of `setup
    configure -v` to ensure that it finds the right package tool (or use
    `--with-hc-pkg` explicitly).


`--with-hc-pkg=`_path_
:   Specify the path to the package tool, e.g. `ghc-pkg`. The package
    tool must be compatible with the compiler specified by
    `--with-compiler`. If this option is omitted, the default value is
    determined from the compiler selected.

`--with-`_`prog`_`=`_path_
:   Specify the path to the program _prog_. Any program known to Cabal
    can be used in place of _prog_. It can either be a fully path or the
    name of a program that can be found on the program search path. For
    example: `--with-ghc=ghc-6.6.1` or
    `--with-cpphs=/usr/local/bin/cpphs`.
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    The full list of accepted programs is not enumerated in this user guide.
    Rather, run `cabal install --help` to view the list.
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`--`_`prog`_`-options=`_options_
:   Specify additional options to the program _prog_. Any program known
    to Cabal can be used in place of _prog_. For example:
    `--alex-options="--template=mytemplatedir/"`. The _options_ is split
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    into program options based on spaces. Any options containing embedded
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    spaced need to be quoted, for example
    `--foo-options='--bar="C:\Program File\Bar"'`. As an alternative
    that takes only one option at a time but avoids the need to quote,
    use `--`_`prog`_`-option` instead.

`--`_`prog`_`-option=`_option_
:   Specify a single additional option to the program _prog_. For
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    passing an option that contain embedded spaces, such as a file name
    with embedded spaces, using this rather than `--`_`prog`_`-options`
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    means you do not need an additional level of quoting. Of course if
    you are using a command shell you may still need to quote, for
    example `--foo-options="--bar=C:\Program File\Bar"`.

All of the options passed with either `--`_`prog`_`-options` or
`--`_`prog`_`-option` are passed in the order they were specified on the
configure command line.

### Installation paths ###

The following options govern the location of installed files from a
package:

`--prefix=`_dir_
:   The root of the installation. For example for a global install you
    might use `/usr/local` on a Unix system, or `C:\Program Files` on a
    Windows system. The other installation paths are usually
    subdirectories of _prefix_, but they don't have to be.

    In the simple build system, _dir_ may contain the following path
    variables: `$pkgid`, `$pkg`, `$version`, `$compiler`, `$os`,
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    `$arch`, `$abi`, `$abitag`
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`--bindir=`_dir_
:   Executables that the user might invoke are installed here.

    In the simple build system, _dir_ may contain the following path
    variables: `$prefix`, `$pkgid`, `$pkg`, `$version`, `$compiler`,
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    `$os`, `$arch`, `$abi`, `$abitag
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`--libdir=`_dir_
:   Object-code libraries are installed here.

    In the simple build system, _dir_ may contain the following path
    variables: `$prefix`, `$bindir`, `$pkgid`, `$pkg`, `$version`,
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    `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--libexecdir=`_dir_
:   Executables that are not expected to be invoked directly by the user
    are installed here.

    In the simple build system, _dir_ may contain the following path
    variables: `$prefix`, `$bindir`, `$libdir`, `$libsubdir`, `$pkgid`,
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    `$pkg`, `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--datadir`=_dir_
:   Architecture-independent data files are installed here.

    In the simple build system, _dir_ may contain the following path
    variables: `$prefix`, `$bindir`, `$libdir`, `$libsubdir`, `$pkgid`, `$pkg`,
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    `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--sysconfdir=`_dir_
:   Installation directory for the configuration files.

    In the simple build system, _dir_ may contain the following path variables:
    `$prefix`, `$bindir`, `$libdir`, `$libsubdir`, `$pkgid`, `$pkg`, `$version`,
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    `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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In addition the simple build system supports the following installation path options:

`--libsubdir=`_dir_
:   A subdirectory of _libdir_ in which libraries are actually
    installed. For example, in the simple build system on Unix, the
    default _libdir_ is `/usr/local/lib`, and _libsubdir_ contains the
    package identifier and compiler, e.g. `mypkg-0.2/ghc-6.4`, so
    libraries would be installed in `/usr/local/lib/mypkg-0.2/ghc-6.4`.

    _dir_ may contain the following path variables: `$pkgid`, `$pkg`,
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    `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--datasubdir=`_dir_
:   A subdirectory of _datadir_ in which data files are actually
    installed.

    _dir_ may contain the following path variables: `$pkgid`, `$pkg`,
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    `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--docdir=`_dir_
:   Documentation files are installed relative to this directory.

    _dir_ may contain the following path variables: `$prefix`, `$bindir`,
    `$libdir`, `$libsubdir`, `$datadir`, `$datasubdir`, `$pkgid`, `$pkg`,
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    `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--htmldir=`_dir_
:   HTML documentation files are installed relative to this directory.

    _dir_ may contain the following path variables: `$prefix`, `$bindir`,
    `$libdir`, `$libsubdir`, `$datadir`, `$datasubdir`, `$docdir`, `$pkgid`,
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    `$pkg`, `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--program-prefix=`_prefix_
:   Prepend _prefix_ to installed program names.

    _prefix_ may contain the following path variables: `$pkgid`, `$pkg`,
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    `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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`--program-suffix=`_suffix_
:   Append _suffix_ to installed program names. The most obvious use for
    this is to append the program's version number to make it possible
    to install several versions of a program at once:
    `--program-suffix='$version'`.

    _suffix_ may contain the following path variables: `$pkgid`, `$pkg`,
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    `$version`, `$compiler`, `$os`, `$arch`, `$abi`, `$abitag`
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#### Path variables in the simple build system ####

For the simple build system, there are a number of variables that can be
used when specifying installation paths. The defaults are also specified
in terms of these variables. A number of the variables are actually for
other paths, like `$prefix`. This allows paths to be specified relative
to each other rather than as absolute paths, which is important for
building relocatable packages (see [prefix
independence](#prefix-independence)).

`$prefix`
:   The path variable that stands for the root of the installation. For
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    an installation to be relocatable, all other installation paths must
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    be relative to the `$prefix` variable.

`$bindir`
:   The path variable that expands to the path given by the `--bindir`
    configure option (or the default).

`$libdir`
:   As above but for `--libdir`

`$libsubdir`
:   As above but for `--libsubdir`

`$datadir`
:   As above but for `--datadir`

`$datasubdir`
:   As above but for `--datasubdir`

`$docdir`
:   As above but for `--docdir`

`$pkgid`
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:   The name and version of the package, e.g. `mypkg-0.2`
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`$pkg`
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:   The name of the package, e.g. `mypkg`
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`$version`
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:   The version of the package, e.g. `0.2`
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`$compiler`
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:   The compiler being used to build the package, e.g. `ghc-6.6.1`
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`$os`
:   The operating system of the computer being used to build the
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    package, e.g. `linux`, `windows`, `osx`, `freebsd` or `solaris`
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`$arch`
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:   The architecture of the computer being used to build the package, e.g.
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    `i386`, `x86_64`, `ppc` or `sparc`

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`$abitag`
:   An optional tag that a compiler can use for telling incompatible ABI's
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    on the same architecture apart. GHCJS encodes the underlying GHC version
    in the ABI tag.
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`$abi`
:   A shortcut for getting a path that completely identifies the platform in terms
    of binary compatibility. Expands to the same value as `$arch-$os-compiler-$abitag`
    if the compiler uses an abi tag, `$arch-$os-$compiler` if it doesn't.

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#### Paths in the simple build system ####

For the simple build system, the following defaults apply:

Option                     Windows Default                                           Unix Default
-------                    ----------------                                          -------------
`--prefix` (global)        `C:\Program Files\Haskell`                                `/usr/local`
`--prefix` (per-user)      `C:\Documents And Settings\user\Application Data\cabal`   `$HOME/.cabal`
`--bindir`                 `$prefix\bin`                                             `$prefix/bin`
`--libdir`                 `$prefix`                                                 `$prefix/lib`
`--libsubdir` (others)     `$pkgid\$compiler`                                        `$pkgid/$compiler`
`--libexecdir`             `$prefix\$pkgid`                                          `$prefix/libexec`
`--datadir` (executable)   `$prefix`                                                 `$prefix/share`
`--datadir` (library)      `C:\Program Files\Haskell`                                `$prefix/share`
`--datasubdir`             `$pkgid`                                                  `$pkgid`
`--docdir`                 `$prefix\doc\$pkgid`                                      `$datadir/doc/$pkgid`
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`--sysconfdir`             `$prefix\etc`                                             `$prefix/etc`
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`--htmldir`                `$docdir\html`                                            `$docdir/html`
`--program-prefix`         (empty)                                                   (empty)
`--program-suffix`         (empty)                                                   (empty)


#### Prefix-independence ####

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On Windows it is possible to obtain the pathname of the running program. This
means that we can construct an installable executable package that is
independent of its absolute install location. The executable can find its
auxiliary files by finding its own path and knowing the location of the other
files relative to `$bindir`.  Prefix-independence is particularly useful: it
means the user can choose the install location (i.e. the value of `$prefix`) at
install-time, rather than having to bake the path into the binary when it is
built.
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In order to achieve this, we require that for an executable on Windows,
all of `$bindir`, `$libdir`, `$datadir` and `$libexecdir` begin with
`$prefix`. If this is not the case then the compiled executable will
have baked-in all absolute paths.

The application need do nothing special to achieve prefix-independence.
If it finds any files using `getDataFileName` and the [other functions
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provided for the
purpose](developing-packages.html#accessing-data-files-from-package-code),
the files will be accessed relative to the location of the current
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executable.

A library cannot (currently) be prefix-independent, because it will be
linked into an executable whose file system location bears no relation
to the library package.

### Controlling Flag Assignments ###

Flag assignments (see the [resolution of conditions and
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flags](developing-packages.html#resolution-of-conditions-and-flags)) can
be controlled with the following command line options.
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`-f` _flagname_ or `-f` `-`_flagname_
:   Force the specified flag to `true` or `false` (if preceded with a `-`). Later
    specifications for the same flags will override earlier, i.e.,
    specifying `-fdebug -f-debug` is equivalent to `-f-debug`

`--flags=`_flagspecs_
:   Same as `-f`, but allows specifying multiple flag assignments at
    once. The parameter is a space-separated list of flag names (to
    force a flag to `true`), optionally preceded by a `-` (to force a
    flag to `false`). For example, `--flags="debug -feature1 feature2"` is
    equivalent to `-fdebug -f-feature1 -ffeature2`.

### Building Test Suites ###

`--enable-tests`
:   Build the test suites defined in the package description file during the
    `build` stage. Check for dependencies required by the test suites. If the
    package is configured with this option, it will be possible to run the test
    suites with the `test` command after the package is built.

`--disable-tests`
:   (default) Do not build any test suites during the `build` stage.
    Do not check for dependencies required only by the test suites. It will not
    be possible to invoke the `test` command without reconfiguring the package.

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`--enable-coverage`
:   Build libraries and executables (including test suites) with Haskell
    Program Coverage enabled. Running the test suites will automatically
    generate coverage reports with HPC.

`--disable-coverage`
:   (default) Do not enable Haskell Program Coverage.

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### Miscellaneous options ##

`--user`
:   Does a per-user installation. This changes the [default installation
    prefix](#paths-in-the-simple-build-system). It also allow
    dependencies to be satisfied by the user's package database, in
    addition to the global database. This also implies a default of
    `--user` for any subsequent `install` command, as packages
    registered in the global database should not depend on packages
    registered in a user's database.

`--global`
:   (default) Does a global installation. In this case package
    dependencies must be satisfied by the global package database. All
    packages in the user's package database will be ignored. Typically
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    the final installation step will require administrative privileges.
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`--package-db=`_db_
:   Allows package dependencies to be satisfied from this additional
    package database _db_ in addition to the global package database.
    All packages in the user's package database will be ignored. The
    interpretation of _db_ is implementation-specific. Typically it will
    be a file or directory. Not all implementations support arbitrary
    package databases.

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    This pushes an extra db onto the db stack. The `--global` and `--user`
    mode switches add the respective [Global] and [Global, User] dbs to the 
    initial stack. There is a compiler-implementation constraint that the
    global db must appear first in the stack, and if the user one appears at
    all, it must appear immediately after the global db.

    To reset the stack, use `--package-db=clear`.

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`--default-user-config=` _file_
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:   Allows a "default" `cabal.config` freeze file to be passed in
    manually. This file will only be used if one does not exist in the
    project directory already. Typically, this can be set from the global
    cabal `config` file so as to provide a default set of partial
    constraints to be used by projects, providing a way for users to peg
    themselves to stable package collections.

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`--enable-optimization`[=_n_] or `-O`[_n_]
:   (default) Build with optimization flags (if available). This is
    appropriate for production use, taking more time to build faster
    libraries and programs.

    The optional _n_ value is the optimisation level. Some compilers
    support multiple optimisation levels. The range is 0 to 2. Level 0
    is equivalent to `--disable-optimization`, level 1 is the default if
    no _n_ parameter is given. Level 2 is higher optimisation if the
    compiler supports it. Level 2 is likely to lead to longer compile
    times and bigger generated code.

`--disable-optimization`
:   Build without optimization. This is suited for development: building
    will be quicker, but the resulting library or programs will be slower.

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`--enable-profiling`
:   Build libraries and executables with profiling enabled (for compilers
    that support profiling as a separate mode). For this to work, all
    libraries used by this package must also have been built with profiling
    support. For libraries this involves building an additional instance of
    the library in addition to the normal non-profiling instance. For
    executables it changes the single executable to be built in profiling mode.

    This flag covers both libraries and executables, but can be overridden
    by the `--enable-library-profiling` flag.

    See also the `--profiling-detail` flag below.

`--disable-profiling`
:   (default) Do not enable profiling in generated libraries and executables.

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`--enable-library-profiling` or `-p`
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:   As with `--enable-profiling` above, but it applies only for libraries. So
    this generates an additional profiling instance of the library in addition
    to the normal non-profiling instance.

    The `--enable-profiling` flag controls the profiling mode for both
    libraries and executables, but if different modes are desired for
    libraries versus executables then use `--enable-library-profiling` as well.
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`--disable-library-profiling`
:   (default) Do not generate an additional profiling version of the
    library.

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`--profiling-detail`[=_level_]
:   Some compilers that support profiling, notably GHC, can allocate costs to
    different parts of the program and there are different levels of
    granularity or detail with which this can be done. In particular for GHC
    this concept is called "cost centers", and GHC can automatically add cost
    centers, and can do so in different ways.

    This flag covers both libraries and executables, but can be overridden
    by the `--library-profiling-detail` flag.

    Currently this setting is ignored for compilers other than GHC. The levels
    that cabal currently supports are:

    `default`
    :    For GHC this uses `exported-functions` for libraries and
         `toplevel-functions` for executables.

    `none`
    :    No costs will be assigned to any code within this component.

    `exported-functions`
    :    Costs will be assigned at the granularity of all top level functions
         exported from each module. In GHC specifically, this is for non-inline
         functions.

    `toplevel-functions`
    :    Costs will be assigned at the granularity of all top level functions
         in each module, whether they are exported from the module or not.
         In GHC specifically, this is for non-inline functions.

    `all-functions`
    :    Costs will be assigned at the granularity of all functions in each
         module, whether top level or local. In GHC specifically, this is for
         non-inline toplevel or where-bound functions or values.

    This flag is new in Cabal-1.24. Prior versions used the equivalent of
    `none` above.

`--library-profiling-detail`[=_level_]
:   As with `--profiling-detail` above, but it applies only for libraries.

    The level for both libraries and executables is set by the
    `--profiling-detail` flag, but if different levels are desired for
    libraries versus executables then use `--library-profiling-detail` as well.
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`--enable-library-vanilla`
:   (default) Build ordinary libraries (as opposed to profiling
    libraries). This is independent of the `--enable-library-profiling`
    option. If you enable both, you get both.

`--disable-library-vanilla`
:   Do not build ordinary libraries. This is useful in conjunction with
    `--enable-library-profiling` to build only profiling libraries,
    rather than profiling and ordinary libraries.

`--enable-library-for-ghci`
:   (default) Build libraries suitable for use with GHCi.

`--disable-library-for-ghci`
:   Not all platforms support GHCi and indeed on some platforms, trying
    to build GHCi libs fails. In such cases this flag can be used as a
    workaround.

`--enable-split-objs`
:   Use the GHC `-split-objs` feature when building the library. This
    reduces the final size of the executables that use the library by
    allowing them to link with only the bits that they use rather than
    the entire library. The downside is that building the library takes
    longer and uses considerably more memory.

`--disable-split-objs`
:   (default) Do not use the GHC `-split-objs` feature. This makes
    building the library quicker but the final executables that use the
    library will be larger.

`--enable-executable-stripping`
:   (default) When installing binary executable programs, run the
    `strip` program on the binary. This can considerably reduce the size
    of the executable binary file. It does this by removing debugging
    information and symbols. While such extra information is useful for
    debugging C programs with traditional debuggers it is rarely helpful
    for debugging binaries produced by Haskell compilers.

    Not all Haskell implementations generate native binaries. For such
    implementations this option has no effect.

`--disable-executable-stripping`
:   Do not strip binary executables during installation. You might want
    to use this option if you need to debug a program using gdb, for
    example if you want to debug the C parts of a program containing
    both Haskell and C code. Another reason is if your are building a
    package for a system which has a policy of managing the stripping
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    itself (such as some Linux distributions).
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`--enable-shared`
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:   Build shared library. This implies a separate compiler run to
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    generate position independent code as required on most platforms.

`--disable-shared`
:   (default) Do not build shared library.

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`--enable-executable-dynamic`
:   Link executables dynamically. The executable's library dependencies should
    be built as shared objects. This implies `--enable-shared` unless
    `--disable-shared` is explicitly specified.

`--disable-executable-dynamic`
:   (default) Link executables statically.

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`--configure-option=`_str_
:   An extra option to an external `configure` script, if one is used
    (see the section on [system-dependent
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    parameters](developing-packages.html#system-dependent-parameters)).
    There can be several of these options.
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`--extra-include-dirs`[=_dir_]
:   An extra directory to search for C header files. You can use this
    flag multiple times to get a list of directories.

    You might need to use this flag if you have standard system header
    files in a non-standard location that is not mentioned in the
    package's `.cabal` file. Using this option has the same affect as
    appending the directory _dir_ to the `include-dirs` field in each
    library and executable in the package's `.cabal` file. The advantage
    of course is that you do not have to modify the package at all.
    These extra directories will be used while building the package and
    for libraries it is also saved in the package registration
    information and used when compiling modules that use the library.

`--extra-lib-dirs`[=_dir_]
:   An extra directory to search for system libraries files. You can use
    this flag multiple times to get a list of directories.

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`--extra-framework-dirs`[=_dir_]
:   An extra directory to search for frameworks (OS X only). You can use this
    flag multiple times to get a list of directories.

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    You might need to use this flag if you have standard system
    libraries in a non-standard location that is not mentioned in the
    package's `.cabal` file. Using this option has the same affect as
    appending the directory _dir_ to the `extra-lib-dirs` field in each
    library and executable in the package's `.cabal` file. The advantage
    of course is that you do not have to modify the package at all.
    These extra directories will be used while building the package and
    for libraries it is also saved in the package registration
    information and used when compiling modules that use the library.

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`--allow-newer`[=_pkgs_]
:   Selectively relax upper bounds in dependencies without editing the
    package description.

    If you want to install a package A that depends on B >= 1.0 && < 2.0, but
    you have the version 2.0 of B installed, you can compile A against B 2.0 by
    using `cabal install --allow-newer=B A`. This works for the whole package
    index: if A also depends on C that in turn depends on B < 2.0, C's
    dependency on B will be also relaxed.

    Example:

    ~~~~~~~~~~~~~~~~
    $ cd foo
    $ cabal configure
    Resolving dependencies...
    cabal: Could not resolve dependencies:
    [...]
    $ cabal configure --allow-newer
    Resolving dependencies...
    Configuring foo...
    ~~~~~~~~~~~~~~~~

    Additional examples:

    ~~~~~~~~~~~~~~~~
    # Relax upper bounds in all dependencies.
    $ cabal install --allow-newer foo

    # Relax upper bounds only in dependencies on bar, baz and quux.
    $ cabal install --allow-newer=bar,baz,quux foo

    # Relax the upper bound on bar and force bar==2.1.
    $ cabal install --allow-newer=bar --constraint="bar==2.1" foo
    ~~~~~~~~~~~~~~~~

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    It's also possible to limit the scope of `--allow-newer` to single
    packages with the `--allow-newer=scope:dep` syntax. This means that the
    dependency on `dep` will be relaxed only for the package `scope`.

    Example:

    ~~~~~~~~~~~~~~~~
    # Relax upper bound in foo's dependency on base; also relax upper bound in
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