NAME

       opam-switch - Manage multiple installation of compilers.

SYNOPSIS

       opam switch [OPTION]... [COMMAND] [ARG]...

DESCRIPTION

       This command allows one to switch between different compiler versions, installing the
       compiler if opam switch is used to switch to that compiler for the first time. The
       different compiler versions are totally independent from each other, meaning that OPAM
       maintains a separate state (e.g. list of installed packages...) for each.

       See the documentation of opam switch list to see the compilers which are available, and
       how to switch or to install a new one.

COMMANDS

       Without argument, defaults to list.

       SWITCH
           With a SWITCH argument, defaults to set SWITCH.

       install SWITCH
           Install the given compiler. The command fails if the switch is already installed (e.g.
           it will not transparently switch to the installed compiler switch, as with set).

       set SWITCH
           Set the currently active switch, installing it if needed.

       remove SWITCH
           Remove the given compiler.

       export FILE
           Save the current switch state to a file.

       import FILE
           Import a saved switch state.

       reinstall SWITCH
           Reinstall the given compiler switch. This will also reinstall all packages.

       list
           List compilers. By default, lists installed and `standard' compilers. Use `--all' to
           get the list of all installable compilers. The first column displays the switch name
           (if any), the second one the switch state (C = current, I = installed, -- = not
           installed), the third one the compiler name and the last one the compiler description.
           To switch to an already installed compiler alias (with state = I), use opam switch
           <name>. If you want to use a new compiler <comp>, use opam switch <comp>: this will
           download, compile and create a fresh and independent environment where new packages
           can be installed. If you want to create a new compiler alias (for instance because you
           already have this compiler version installed), use opam switch <name> --alias-of
           <comp>. In case <name> and <comp> are the same, this is equivalent to opam switch
           <comp>.

       show
           Show the current compiler.

OPTIONS

       -A COMP, --alias-of=COMP
           The name of the compiler description which will be aliased.

       -a, --all
           List all the compilers which can be installed on the system.

       -b, --keep-build-dir
           Keep the build directory. This is equivalent to setting $OPAMKEEPBUILDDIR to "true".

       -d, --build-doc
           Build the package documentation. This is equivalent to setting $OPAMBUILDDOC to
           "true".

       --dry-run
           Simulate the command, but don't actually perform any changes.

       -e TAGS, --external=TAGS
           Display the external packages associated to the given tags. This is deprecated, use
           `opam list --external' instead

       --fake
           This option registers the actions into the OPAM database, without actually performing
           them. WARNING: This option is dangerous and likely to break your OPAM environment. You
           probably want `--dry-run'. You've been warned.

       -i, --installed
           List installed compiler switches only.

       -j JOBS, --jobs=JOBS
           Set the maximal number of concurrent jobs to use. You can also set it using the
           $OPAMJOBS environment variable.

       --json=FILENAME
           Save the result output of an OPAM run in a computer-readable file

       -m MAKE, --make=MAKE
           Use MAKE as the default 'make' command.

       --no-checksums
           Do not verify the checksum of downloaded archives.This is equivalent to setting
           $OPAMNOCHECKSUMS to "true".

       --no-switch
           Only install the compiler switch, without switching to it. If the compiler switch is
           already installed, then do nothing.

       --no-warning
           Do not display any warning related to environment variables.

       --require-checksums
           Reject the installation of packages that don't provide a checksum for the upstream
           archives. This is equivalent to setting $OPAMREQUIRECHECKSUMS to "true".

       -s, --short
           Output raw lists of names, one per line, skipping any details.

       --show-actions
           Call the solver and display the actions. Don't perform any changes.

       -t, --build-test
           Build and run the package unit-tests. This is equivalent to setting $OPAMBUILDTEST to
           "true".

COMMON OPTIONS

       These options are common to all commands.

       --color=WHEN (absent=auto)
           Colorize the output. WHEN must be one of `always', `never' or `auto'.

       --criteria=CRITERIA
           Specify user preferences for dependency solving for this run. Overrides both
           $OPAMCRITERIA and $OPAMUPGRADECRITERIA. For details on the supported language, and the
           external solvers available, see
           http://opam.ocaml.org/doc/Specifying_Solver_Preferences.html. A general guide to using
           solver preferences can be found at  http://www.dicosmo.org/Articles/usercriteria.pdf.
           The default value is
           -count(down),-count(removed),-notuptodate(solution),-sum(solution,version-lag),-count(new)
           for upgrades, and
           -count(removed),-notuptodate(request),-sum(request,version-lag),-count(down),-notuptodate(changed),-count(changed),-notuptodate(solution),-sum(solution,version-lag)
           otherwise.

       --cudf=FILENAME
           Debug option: Save the CUDF requests sent to the solver to FILENAME-<n>.cudf.

       --debug
           Print debug message to stderr. This is equivalent to setting $OPAMDEBUG to "true".

       --debug-level=LEVEL
           Like `--debug', but allows specifying the debug level (`--debug' sets it to 1).
           Equivalent to setting $OPAMDEBUG to a positive integer.

       --git-version
           Print the git version if it exists and exit.

       --help[=FMT] (default=pager)
           Show this help in format FMT (pager, plain or groff).

       --no-base-packages
           Do not install base packages (useful for testing purposes). This is equivalent to
           setting $OPAMNOBASEPACKAGES to a non-empty string.

       --no-self-upgrade
           OPAM will replace itself with a newer binary found at OPAMROOT/opam if present. This
           disables this behaviour.

       -q, --quiet
           Be quiet when installing a new compiler.

       --root=ROOT (absent=~/.opam)
           Use ROOT as the current root path. This is equivalent to setting $OPAMROOT to ROOT.

       --safe
           Make sure nothing will be automatically updated or rewritten. Useful for calling from
           completion scripts, for example. Will fail whenever such an operation is needed ; also
           avoids waiting for locks, skips interactive questions and overrides the OPAMDEBUG
           variable.

       --solver=CMD
           Specify the name of the external dependency solver. The default value is aspcud.
           Either 'aspcud', 'packup' or a custom command that may contain the variables
           %{input}%, %{output}% and %{criteria}%

       --strict
           Fail whenever an error is found in a package definition or a configuration file. The
           default is to continue silently if possible.

       --switch=SWITCH
           Use SWITCH as the current compiler switch. This is equivalent to setting $OPAMSWITCH
           to SWITCH.

       --use-internal-solver, --no-aspcud
           Force use of internal heuristics, even if an external solver is available.

       -v, --verbose
           Be more verbose, show package sub-commands and their output. Repeat to see more.
           Repeating n times is equivalent to setting $OPAMVERBOSE to "n".

       --version
           Show version information.

       -y, --yes
           Disable interactive mode and answer yes to all questions that would otherwise be asked
           to the user. This is equivalent to setting $OPAMYES to "true".

ENVIRONMENT VARIABLES

       OPAM makes use of the environment variables listed here. Boolean variables should be set
       to "0", "no" of "false" to disable, "1", "yes" or "true" to enable.

       OPAMCOLOR, when set to always or never, sets a default value for the --color option.

       OPAMCRITERIA specifies user preferences for dependency solving.The default value is
       -count(removed),-notuptodate(request),-sum(request,version-lag),-count(down),-notuptodate(changed),-count(changed),-notuptodate(solution),-sum(solution,version-lag).
       See also option --criteria

       OPAMCURL can be used to select a given 'curl' program. See OPAMFETCH for more options.

       OPAMDEBUG see options `--debug' and `--debug-level'.

       OPAMDOWNLOADJOBS sets the maximum number of simultaneous downloads.

       OPAMEXTERNALSOLVER see option `--solver'.

       OPAMFETCH specifies how to download files: either `wget', `curl' or a custom command where
       variables %{url}%, %{out}%, %{retries}%, %{compress}% and %{checksum}% will be replaced.
       Overrides the 'download-command' value from the main config file.

       OPAMJOBS sets the maximum number of parallel workers to run.

       OPAMLOCKRETRIES sets the number of tries after which OPAM gives up acquiring its lock and
       fails. <= 0 means infinite wait.

       OPAMNO answer no to any question asked.

       OPAMNOASPCUD see option `--no-aspcud'.

       OPAMNOSELFUPGRADE see option `--no-self-upgrade'.

       OPAMPINKINDAUTO if set, version control systems are detected when pinning to a local path.

       OPAMREQUIRECHECKSUMS see option `--require-checksums'.

       OPAMRETRY sets the number of tries before failing downloads.

       OPAMROOT see option `--root'. This is automatically set by `opam config env --root=DIR'
       when DIR is non-default or OPAMROOT is already defined.

       OPAMSAFE see option `--safe'

       OPAMSKIPVERSIONCHECKS bypasses some version checks. Unsafe, for compatibility testing
       only.

       OPAMSOLVERTIMEOUT change the time allowance of the internal solver.

       OPAMSTATUSLINE display a dynamic status line showing what's currently going on on the
       terminal. (one of one of `always', `never' or `auto')

       OPAMSWITCH see option `--switch'. Automatically set by `opam config env --switch=SWITCH'.

       OPAMUPGRADECRITERIA specifies user preferences for dependency solving when performing an
       upgrade. Overrides OPAMCRITERIA in upgrades if both are set.The default value is
       -count(down),-count(removed),-notuptodate(solution),-sum(solution,version-lag),-count(new).
       See also option --criteria

       OPAMUSEINTERNALSOLVER see option `--use-internal-solver'.

       OPAMUTF8 use UTF8 characters in output (one of one of `always', `never' or `auto'). By
       default `auto', which is determined from the locale).

       OPAMUTF8MSGS use extended UTF8 characters (camels) in OPAM messages. Implies OPAMUTF8.
       This is set by default on OSX only.

       OPAMVAR_var overrides the contents of the variable var when substituting `%{var}%` strings
       in `opam` files.

       OPAMVAR_package_var overrides the contents of the variable package:var when substituting
       `%{package:var}%` strings in `opam` files.

       OPAMVERBOSE see option `--verbose'.

       OPAMYES see option `--yes'.

FURTHER DOCUMENTATION

       See https://opam.ocaml.org.

AUTHORS

       Thomas Gazagnaire <thomas@gazagnaire.org>
       Anil Madhavapeddy <anil@recoil.org>
       Fabrice Le Fessant <Fabrice.Le_fessant@inria.fr>
       Frederic Tuong <tuong@users.gforge.inria.fr>
       Louis Gesbert <louis.gesbert@ocamlpro.com>
       Vincent Bernardoff <vb@luminar.eu.org>
       Guillem Rieu <guillem.rieu@ocamlpro.com>
       Roberto Di Cosmo <roberto@dicosmo.org>

BUGS

       Check bug reports at https://github.com/ocaml/opam/issues.