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.

Module loading

  • RAKUDOLIB, RAKULIB (Str; src/core/Inc.pm)

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.

  • RAKUDO_MODULE_DEBUG (Bool; src/Perl6/ModuleLoader.nqp)

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

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. NOTE: This env var was added in version 6.e. Early implementation has been available in Rakudo compiler as of version 2019.12, and before that it was available as PERL6_EXCEPTIONS_HANDLER.

  • RAKUDO_NO_DEPRECATIONS (Bool; src/core.c/Deprecations.pm6)

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

  • RAKUDO_DEPRECATIONS_FATAL (Bool; src/core.c/Deprecations.pm6)

If true, deprecation warnings become thrown exceptions.

  • RAKUDO_VERBOSE_STACKFRAME (UInt; src/core.c/Backtrace.pm6)

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.

  • RAKUDO_BACKTRACE_SETTING (Bool; src/core.c/Backtrace.pm6)

Controls whether .setting files are included in backtraces.

Affecting precompilation

  • RAKUDO_PREFIX (Str; src/core.c/CompUnit/RepositoryRegistry.pm6)

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.

  • RAKUDO_PRECOMP_DIST (src/core.c/CompUnit/PrecompilationRepository.pm6)

  • RAKUDO_PRECOMP_LOADING (src/core.c/CompUnit/PrecompilationRepository.pm6)

  • RAKUDO_PRECOMP_WITH (src/core.c/CompUnit/PrecompilationRepository.pm6)

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.

Line editor


This specifies the preferred line editor to use; valid values are 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.

  • RAKUDO_ERROR_COLOR (Bool; src/core.c/Exception.pm6)

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

  • RAKUDO_MAX_THREADS (UInt; src/core.c/ThreadPoolScheduler.pm6)

Indicates the maximum number of threads used by default when creating a ThreadPoolScheduler. Defaults to 64.

  • TMPDIR, TEMP, TMP (Str; src/core.c/IO/Spec/)

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 (Str; src/core.c/IO/Spec/)

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