Rakudo's behavior can be tweaked by a (growing) number of environment variables; this section attempts to document all those currently in use. They are interpreter specific in all cases, except where some use conventional names such as PATH.

The underlying virtual machine is also sensitive to a series of environment variables; they are listed in this wiki page.

Affecting execution from the command line§


Available as of the 2022.02 Rakudo compiler release.

The RAKUDO_OPT environment variable provides a way to specify default compiler command line options, overridable by explicitly specifications on the command line. For example:

    RAKUDO_OPT="-I. --ll-exception" raku -Ilib test.raku

would ignore the -I. but would honor the --ll-exception command line argument.

A simple space splitter is used to separate arguments, making it impossible to use a arguments with spaces in them.

Module loading§


Type: Str.

RAKUDOLIB and RAKULIB append a comma-delimited list of paths to the search list for modules. RAKUDOLIB is evaluated first. NOTE: These env vars were added in the Rakudo compiler in version 2020.05. The deprecated older env var PERL6LIB is still available.


Type: Bool.

If true, causes the module loader to print debugging information to standard error.


Type: Bool.

Available as of the 2012.12 release of the Rakudo compiler.

If true, causes the module loader to print the names of modules that are being re-precompiled on standard error. As such it is a simplified version of the functionality offered by RAKUDO_MODULE_DEBUG.

Error message verbosity and strictness§


If present, the print_exception routine will use a class of that name to process the exception for output. Rakudo currently ships with Exceptions::JSON (invoked by setting this variable to JSON), to override the default output.

Available as of the 2020.01 release of the Rakudo compiler. Before that it was available as PERL6_EXCEPTIONS_HANDLER (which was removed in the 2023.04 release of the Rakudo compiler).

Intended to be used by environments that embed the Raku Programming Language, such as IDEs.

    RAKU_EXCEPTIONS_HANDLER=JSON raku -e 'die "foo"'
    # {"X::AdHoc":{"payload":"foo","message":"foo"}}


Type: Bool.

If true, suppresses deprecation warnings triggered by the is DEPRECATED trait.


Type: Bool.

If true, deprecation warnings become thrown exceptions.


Type: UInt.

Displays source code in stack frames surrounded by the specified number of lines of context; for instance RAKUDO_VERBOSE_STACKFRAME = 1 will use one context line.


Type: Bool.

Controls whether .setting files are included in backtraces.

Affecting precompilation§


Type: Str.

When this is set, Rakudo will look for the standard repositories (perl, vendor, site) in the specified directory. This is intended as an escape hatch for build-time bootstrapping issues, where Rakudo may be built as an unprivileged user without write access to the runtime paths in NQP's config.




These are internal variables for passing serialized state to precompilation jobs in child processes. Please do not set them manually.


If set to 1, diagnostic information about the precompilation process is emitted.


If set to 1, precompilation will be disabled. Available as of the 2023.08 release of the Rakudo compiler.

REPL (Read-eval-print loop)§


This specifies the name of the method that should be called on the result value of a statement in the REPL if the statement did not cause any output of its own. If absent, gist will be assumed. One can use raku to force a more literal, parsable representation. Or Str to force a complete string representation. Available as of the 2020.06 release of the Rakudo compiler.


This specifies the preferred line editor to use; valid values are LineEditor, Readline, Linenoise, and none. A value of none is useful if you want to avoid the recommendation message upon REPL startup.


If set to 1, will disable multiline input for the REPL.


This specifies the location of the history file used by the line editor; the default is ~/.raku/rakudo-history. Before Rakudo version 2020.02 the default was ~/.perl6/rakudo-history.



This specifies the default number of characters to read on an IO::Handle by setting the $*DEFAULT-READ-ELEMS dynamic variable.


Type: Bool.

Controls whether to emit ANSI codes for error highlighting. Defaults to true if unset, except on Windows.


Supported as of release 2022.04 of the Rakudo compiler. If specified with a true value, will not try to load any of the line editing modules in the REPL. This allows the REPL to be better integrated in the Emacs environment (which sets this environment variable).


Type: UInt.

Indicates the maximum number of threads used by default when creating a ThreadPoolScheduler. Defaults to 64 unless there appear to be more than 8 CPU cores available: in which case it defaults to 8 * number of cores.

As of release 2022.06 of the Rakudo compiler, it is also possible to specify "unlimited" or "Inf" to indicate that the number of threads available by the operating system, will be the limiting factor.


Type: Str.

The IO::Spec::Unix.tmpdir method will return $TMPDIR if it points to a directory with full access permissions for the current user, with a fallback default of '/tmp'.

IO::Spec::Cygwin and IO::Spec::Win32 use more Windows-appropriate lists which also include the %TEMP% and %TMP% environment variables.

  • PATH, Path

Type: Str.

The IO::Spec::Unix.path method splits $PATH as a shell would; i.e. as a colon-separated list. IO::Spec::Cygwin inherits this from IO::Spec::Unix. IO::Spec::Win32.path will read the first defined of either %PATH% or %Path% as a semicolon-delimited list.


Indicates the period in which the telemetry snapper will take a snapshot. Defaults to .1 for 10 snapshots per second.


Allows to override the Raku installation path. Defaults to [rakudo_executable_dir]/../share/perl6 in relocatable builds and the absolute path to that folder in non-relocatable builds.


Allows to override the NQP installation path. Defaults to [rakudo_executable_dir]/../share/nqp in relocatable builds and the absolute path to that folder in non-relocatable builds.


Non-console applications§

On Windows programs are compiled to either be console applications or non-console applications. Console applications always open a console window. There is no straightforward way to suppress this window.

Rakudo provides a separate set of executables suffixed with a 'w' (rakuw.exe, rakudow.exe, ...) that are compiled as non-console applications. These do not spawn this console window.

WARNING By default these non-console applications will silently swallow everything that is printed to STDOUT and STDERR.

To receive the output of the program it suffices to redirect it externally:

rakuw.exe script.raku >stdout.txt 2>stderr.txt