6. cabal-install Commands

We now give an in-depth description of all the commands, describing the arguments and flags they accept.

6.1. cabal v2-configure

cabal v2-configure takes a set of arguments and writes a cabal.project.local file based on the flags passed to this command. cabal v2-configure FLAGS; cabal new-build is roughly equivalent to cabal v2-build FLAGS, except that with new-configure the flags are persisted to all subsequent calls to v2-build.

cabal v2-configure is intended to be a convenient way to write out a cabal.project.local for simple configurations; e.g., cabal v2-configure -w ghc-7.8 would ensure that all subsequent builds with cabal v2-build are performed with the compiler ghc-7.8. For more complex configuration, we recommend writing the cabal.project.local file directly (or placing it in cabal.project!)

cabal v2-configure inherits options from Cabal. semantics:

  • Any flag accepted by ./Setup configure.
  • Any flag accepted by cabal configure beyond ./Setup configure, namely --cabal-lib-version, --constraint, --preference and --solver.
  • Any flag accepted by cabal install beyond ./Setup configure.
  • Any flag accepted by ./Setup haddock.

The options of all of these flags apply only to local packages in a project; this behavior is different than that of cabal install, which applies flags to every package that would be built. The motivation for this is to avoid an innocuous addition to the flags of a package resulting in a rebuild of every package in the store (which might need to happen if a flag actually applied to every transitive dependency). To apply options to an external package, use a package stanza in a cabal.project file.

6.2. cabal v2-update

cabal v2-update updates the state of the package index. If the project contains multiple remote package repositories it will update the index of all of them (e.g. when using overlays).

Some examples:

$ cabal v2-update                  # update all remote repos
$ cabal v2-update head.hackage     # update only head.hackage

6.3. cabal v2-build

cabal v2-build takes a set of targets and builds them. It automatically handles building and installing any dependencies of these targets.

A target can take any of the following forms:

  • A package target: package, which specifies that all enabled components of a package to be built. By default, test suites and benchmarks are not enabled, unless they are explicitly requested (e.g., via --enable-tests.)

  • A component target: [package:][ctype:]component, which specifies a specific component (e.g., a library, executable, test suite or benchmark) to be built.

  • All packages: all, which specifies all packages within the project.

  • Components of a particular type: package:ctypes, all:ctypes: which specifies all components of the given type. Where valid ctypes are:

    • libs, libraries,
    • flibs, foreign-libraries,
    • exes, executables,
    • tests,
    • benches, benchmarks.
  • A module target: [package:][ctype:]module, which specifies that the component of which the given module is a part of will be built.

  • A filepath target: [package:][ctype:]filepath, which specifies that the component of which the given filepath is a part of will be built.

In component targets, package: and ctype: (valid component types are lib, flib, exe, test and bench) can be used to disambiguate when multiple packages define the same component, or the same component name is used in a package (e.g., a package foo defines both an executable and library named foo). We always prefer interpreting a target as a package name rather than as a component name.

Some example targets:

$ cabal v2-build lib:foo-pkg       # build the library named foo-pkg
$ cabal v2-build foo-pkg:foo-tests # build foo-tests in foo-pkg
$ cabal v2-build src/Lib.s         # build the library component to
                                   # which "src/Lib.hs" belongs
$ cabal v2-build app/Main.hs       # build the executable component of
                                   # "app/Main.hs"
$ cabal v2-build Lib               # build the library component to
                                   # which the module "Lib" belongs

Beyond a list of targets, cabal v2-build accepts all the flags that cabal v2-configure takes. Most of these flags are only taken into consideration when building local packages; however, some flags may cause extra store packages to be built (for example, --enable-profiling will automatically make sure profiling libraries for all transitive dependencies are built and installed.)

In addition cabal v2-build accepts these flags:

  • --only-configure: When given we will forgoe performing a full build and abort after running the configure phase of each target package.

6.4. cabal v2-repl

cabal v2-repl TARGET loads all of the modules of the target into GHCi as interpreted bytecode. In addition to cabal v2-build’s flags, it takes an additional --repl-options flag.

To avoid ghci specific flags from triggering unneeded global rebuilds these flags are now stripped from the internal configuration. As a result --ghc-options will no longer (reliably) work to pass flags to ghci (or other repls). Instead, you should use the new --repl-options flag to specify these options to the invoked repl. (This flag also works on cabal repl and Setup repl on sufficiently new versions of Cabal.)

Currently, it is not supported to pass multiple targets to v2-repl (v2-repl will just successively open a separate GHCi session for each target.)

It also provides a way to experiment with libraries without needing to download them manually or to install them globally.

This command opens a REPL with the current default target loaded, and a version of the vector package matching that specification exposed.

$ cabal v2-repl --build-depends "vector >= 0.12 && < 0.13"

Both of these commands do the same thing as the above, but only exposes base, vector, and the vector package’s transitive dependencies even if the user is in a project context.

$ cabal v2-repl --ignore-project --build-depends "vector >= 0.12 && < 0.13"
$ cabal v2-repl --project='' --build-depends "vector >= 0.12 && < 0.13"

This command would add vector, but not (for example) primitive, because it only includes the packages specified on the command line (and base, which cannot be excluded for technical reasons).

$ cabal v2-repl --build-depends vector --no-transitive-deps

6.5. cabal v2-run

cabal v2-run [TARGET [ARGS]] runs the executable specified by the target, which can be a component, a package or can be left blank, as long as it can uniquely identify an executable within the project. Tests and benchmarks are also treated as executables.

See the v2-build section for the target syntax.

Except in the case of the empty target, the strings after it will be passed to the executable as arguments.

If one of the arguments starts with - it will be interpreted as a cabal flag, so if you need to pass flags to the executable you have to separate them with --.

$ cabal v2-run target -- -a -bcd --argument

‘v2-run’ also supports running script files that use a certain format. With a script that looks like:

#!/usr/bin/env cabal
{- cabal:
build-depends: base ^>= 4.11
            , shelly ^>= 1.8.1
-}

main :: IO ()
main = do
    ...

It can either be executed like any other script, using cabal as an interpreter, or through this command:

$ cabal v2-run script.hs
$ cabal v2-run script.hs -- --arg1 # args are passed like this

6.6. cabal v2-freeze

cabal v2-freeze writes out a freeze file which records all of the versions and flags which that are picked by the solver under the current index and flags. Default name of this file is cabal.project.freeze but in combination with a --project-file=my.project flag (see project-file) the name will be my.project.freeze. A freeze file has the same syntax as cabal.project and looks something like this:

constraints: HTTP ==4000.3.3,
             HTTP +warp-tests -warn-as-error -network23 +network-uri -mtl1 -conduit10,
             QuickCheck ==2.9.1,
             QuickCheck +templatehaskell,
             -- etc...

For end-user executables, it is recommended that you distribute the cabal.project.freeze file in your source repository so that all users see a consistent set of dependencies. For libraries, this is not recommended: users often need to build against different versions of libraries than what you developed against.

6.7. cabal v2-bench

cabal v2-bench [TARGETS] [OPTIONS] runs the specified benchmarks (all the benchmarks in the current package by default), first ensuring they are up to date.

6.8. cabal v2-test

cabal v2-test [TARGETS] [OPTIONS] runs the specified test suites (all the test suites in the current package by default), first ensuring they are up to date.

6.9. cabal v2-haddock

cabal v2-haddock [FLAGS] [TARGET] builds Haddock documentation for the specified packages within the project.

If a target is not a library haddock-benchmarks, haddock-executables, haddock-internal, haddock-tests will be implied as necessary.

6.10. cabal v2-exec

cabal v2-exec [FLAGS] [--] COMMAND [--] [ARGS] runs the specified command using the project’s environment. That is, passing the right flags to compiler invocations and bringing the project’s executables into scope.

6.11. cabal v2-install

cabal v2-install [FLAGS] PACKAGES builds the specified packages and symlinks/copies their executables in installdir (usually ~/.cabal/bin).

For example this command will build the latest cabal-install and symlink its cabal executable:

$ cabal v2-install cabal-install

In addition, it’s possible to use cabal v2-install to install components of a local project. For example, with an up-to-date Git clone of the Cabal repository, this command will build cabal-install HEAD and symlink the cabal executable:

$ cabal v2-install exe:cabal

Where symlinking is not possible (eg. on some Windows versions) the copy method is used by default. You can specify the install method by using --install-method flag:

$ cabal v2-install exe:cabal --install-method=copy --installdir=$HOME/bin

Note that copied executables are not self-contained, since they might use data-files from the store.

It is also possible to “install” libraries using the --lib flag. For example, this command will build the latest Cabal library and install it:

$ cabal v2-install --lib Cabal

This works by managing GHC environments. By default, it is writing to the global environment in ~/.ghc/$ARCH-$OS-$GHCVER/environments/default. v2-install provides the --package-env flag to control which of these environments is modified.

This command will modify the environment file in the current directory:

$ cabal v2-install --lib Cabal --package-env .

This command will modify the environment file in the ~/foo directory:

$ cabal v2-install --lib Cabal --package-env foo/

Do note that the results of the previous two commands will be overwritten by the use of other v2-style commands, so it is not recommended to use them inside a project directory.

This command will modify the environment in the “local.env” file in the current directory:

$ cabal v2-install --lib Cabal --package-env local.env

This command will modify the myenv named global environment:

$ cabal v2-install --lib Cabal --package-env myenv

If you wish to create a named environment file in the current directory where the name does not contain an extension, you must reference it as ./myenv.

You can learn more about how to use these environments in this section of the GHC manual.

6.12. cabal v2-clean

cabal v2-clean [FLAGS] cleans up the temporary files and build artifacts stored in the dist-newstyle folder.

By default, it removes the entire folder, but it can also spare the configuration and caches if the --save-config option is given, in which case it only removes the build artefacts (.hi, .o along with any other temporary files generated by the compiler, along with the build output).

6.13. cabal v2-sdist

cabal v2-sdist [FLAGS] [TARGETS] takes the crucial files needed to build TARGETS and puts them into an archive format ready for upload to Hackage. These archives are stable and two archives of the same format built from the same source will hash to the same value.

cabal v2-sdist takes the following flags:

  • -l, --list-only: Rather than creating an archive, lists files that would be included. Output is to stdout by default. The file paths are relative to the project’s root directory.
  • -o, --output-directory: Sets the output dir, if a non-default one is desired. The default is dist-newstyle/sdist/. --output-directory - will send output to stdout unless multiple archives are being created.
  • --null-sep: Only used with --list-only. Separates filenames with a NUL byte instead of newlines.

v2-sdist is inherently incompatible with sdist hooks (which were removed in Cabal-3.0), not due to implementation but due to fundamental core invariants (same source code should result in the same tarball, byte for byte) that must be satisfied for it to function correctly in the larger v2-build ecosystem. autogen-modules is able to replace uses of the hooks to add generated modules, along with the custom publishing of Haddock documentation to Hackage.

Warning

Packages that use Backpack will stop working if uploaded to Hackage, due to issue #6005. While this is happening, we recommend not uploading these packages to Hackage (and instead referencing the package directly as a source-repository-package).