NAME
Module::Runtime - runtime module handling
SYNOPSIS
use Module::Runtime qw(
$module_name_rx is_module_name check_module_name
module_notional_filename require_module);
if($module_name =~ /\A$module_name_rx\z/o) { ...
if(is_module_name($module_name)) { ...
check_module_name($module_name);
$notional_filename = module_notional_filename($module_name);
require_module($module_name);
use Module::Runtime qw(use_module use_package_optimistically);
$bi = use_module("Math::BigInt", 1.31)->new("1_234");
$widget = use_package_optimistically("Local::Widget")->new;
use Module::Runtime qw(
$top_module_spec_rx $sub_module_spec_rx
is_module_spec check_module_spec
compose_module_name);
if($spec =~ /\A$top_module_spec_rx\z/o) { ...
if($spec =~ /\A$sub_module_spec_rx\z/o) { ...
if(is_module_spec("Standard::Prefix", $spec)) { ...
check_module_spec("Standard::Prefix", $spec);
$module_name = compose_module_name("Standard::Prefix", $spec);
DESCRIPTION
The functions exported by this module deal with runtime handling of Perl
modules, which are normally handled at compile time. This module avoids
using any other modules, so that it can be used in low-level
infrastructure.
The parts of this module that work with module names apply the same
syntax that is used for barewords in Perl source. In principle this
syntax can vary between versions of Perl, and this module applies the
syntax of the Perl on which it is running. In practice the usable syntax
hasn't changed yet. There's some intent for Unicode module names to be
supported in the future, but this hasn't yet amounted to any consistent
facility.
The functions of this module whose purpose is to load modules include
workarounds for three old Perl core bugs regarding "require". These
workarounds are applied on any Perl version where the bugs exist, except
for a case where one of the bugs cannot be adequately worked around in
pure Perl.
Module name syntax
The usable module name syntax has not changed from Perl 5.000 up to Perl
5.19.8. The syntax is composed entirely of ASCII characters. From Perl
5.6 onward there has been some attempt to allow the use of non-ASCII
Unicode characters in Perl source, but it was fundamentally broken (like
the entirety of Perl 5.6's Unicode handling) and remained pretty much
entirely unusable until it got some attention in the Perl 5.15 series.
Although Unicode is now consistently accepted by the parser in some
places, it remains broken for module names. Furthermore, there has not
yet been any work on how to map Unicode module names into filenames, so
in that respect also Unicode module names are unusable.
The module name syntax is, precisely: the string must consist of one or
more segments separated by "::"; each segment must consist of one or
more identifier characters (ASCII alphanumerics plus "_"); the first
character of the string must not be a digit. Thus ""IO::File"",
""warnings"", and ""foo::123::x_0"" are all valid module names, whereas
""IO::"" and ""1foo::bar"" are not. "'" separators are not permitted by
this module, though they remain usable in Perl source, being translated
to "::" in the parser.
Core bugs worked around
The first bug worked around is core bug [perl #68590], which causes
lexical state in one file to leak into another that is "require"d/"use"d
from it. This bug is present from Perl 5.6 up to Perl 5.10, and is fixed
in Perl 5.11.0. From Perl 5.9.4 up to Perl 5.10.0 no satisfactory
workaround is possible in pure Perl. The workaround means that modules
loaded via this module don't suffer this pollution of their lexical
state. Modules loaded in other ways, or via this module on the Perl
versions where the pure Perl workaround is impossible, remain
vulnerable. The module Lexical::SealRequireHints provides a complete
workaround for this bug.
The second bug worked around causes some kinds of failure in module
loading, principally compilation errors in the loaded module, to be
recorded in %INC as if they were successful, so later attempts to load
the same module immediately indicate success. This bug is present up to
Perl 5.8.9, and is fixed in Perl 5.9.0. The workaround means that a
compilation error in a module loaded via this module won't be cached as
a success. Modules loaded in other ways remain liable to produce bogus
%INC entries, and if a bogus entry exists then it will mislead this
module if it is used to re-attempt loading.
The third bug worked around causes the wrong context to be seen at file
scope of a loaded module, if "require" is invoked in a location that
inherits context from a higher scope. This bug is present up to Perl
5.11.2, and is fixed in Perl 5.11.3. The workaround means that a module
loaded via this module will always see the correct context. Modules
loaded in other ways remain vulnerable.
REGULAR EXPRESSIONS
These regular expressions do not include any anchors, so to check
whether an entire string matches a syntax item you must supply the
anchors yourself.
$module_name_rx
Matches a valid Perl module name in bareword syntax.
$top_module_spec_rx
Matches a module specification for use with "compose_module_name".
where no prefix is being used.
$sub_module_spec_rx
Matches a module specification for use with "compose_module_name",
where a prefix is being used.
FUNCTIONS
Basic module handling
is_module_name(ARG)
Returns a truth value indicating whether *ARG* is a plain string
satisfying Perl module name syntax as described for
"$module_name_rx".
is_valid_module_name(ARG)
Deprecated alias for "is_module_name".
check_module_name(ARG)
Check whether *ARG* is a plain string satisfying Perl module name
syntax as described for "$module_name_rx". Return normally if it is,
or "die" if it is not.
module_notional_filename(NAME)
Generates a notional relative filename for a module, which is used
in some Perl core interfaces. The *NAME* is a string, which should
be a valid module name (one or more "::"-separated segments). If it
is not a valid name, the function "die"s.
The notional filename for the named module is generated and
returned. This filename is always in Unix style, with "/" directory
separators and a ".pm" suffix. This kind of filename can be used as
an argument to "require", and is the key that appears in %INC to
identify a module, regardless of actual local filename syntax.
require_module(NAME)
This is essentially the bareword form of "require", in runtime form.
The *NAME* is a string, which should be a valid module name (one or
more "::"-separated segments). If it is not a valid name, the
function "die"s.
The module specified by *NAME* is loaded, if it hasn't been already,
in the manner of the bareword form of "require". That means that a
search through @INC is performed, and a byte-compiled form of the
module will be used if available.
The return value is as for "require". That is, it is the value
returned by the module itself if the module is loaded anew, or 1 if
the module was already loaded.
Structured module use
use_module(NAME[, VERSION])
This is essentially "use" in runtime form, but without the importing
feature (which is fundamentally a compile-time thing). The *NAME* is
handled just like in "require_module" above: it must be a module
name, and the named module is loaded as if by the bareword form of
"require".
If a *VERSION* is specified, the "VERSION" method of the loaded
module is called with the specified *VERSION* as an argument. This
normally serves to ensure that the version loaded is at least the
version required. This is the same functionality provided by the
*VERSION* parameter of "use".
On success, the name of the module is returned. This is unlike
"require_module", and is done so that the entire call to
"use_module" can be used as a class name to call a constructor, as
in the example in the synopsis.
use_package_optimistically(NAME[, VERSION])
This is an analogue of "use_module" for the situation where there is
uncertainty as to whether a package/class is defined in its own
module or by some other means. It attempts to arrange for the named
package to be available, either by loading a module or by doing
nothing and hoping.
An attempt is made to load the named module (as if by the bareword
form of "require"). If the module cannot be found then it is assumed
that the package was actually already loaded by other means, and no
error is signaled. That's the optimistic bit.
*Warning:* this optional module loading is liable to cause
unreliable behaviour, including security problems. It interacts
especially badly with having "." in @INC, which was the default
state of affairs in Perls prior to 5.25.11. If a package is actually
defined by some means other than a module, then applying this
function to it causes a spurious attempt to load a module that is
expected to be non-existent. If a module actually exists under that
name then it will be unintentionally loaded. If "." is in @INC and
this code is ever run with the current directory being one writable
by a malicious user (such as /tmp), then the malicious user can
easily cause the victim to run arbitrary code, by creating a module
file under the predictable spuriously-loaded name in the writable
directory. Generally, optional module loading should be avoided.
This is mostly the same operation that is performed by the base
pragma to ensure that the specified base classes are available. The
behaviour of base was simplified in version 2.18, and later improved
in version 2.20, and on both occasions this function changed to
match.
If a *VERSION* is specified, the "VERSION" method of the loaded
package is called with the specified *VERSION* as an argument. This
normally serves to ensure that the version loaded is at least the
version required. On success, the name of the package is returned.
These aspects of the function work just like "use_module".
Module name composition
is_module_spec(PREFIX, SPEC)
Returns a truth value indicating whether *SPEC* is valid input for
"compose_module_name". See below for what that entails. Whether a
*PREFIX* is supplied affects the validity of *SPEC*, but the exact
value of the prefix is unimportant, so this function treats *PREFIX*
as a truth value.
is_valid_module_spec(PREFIX, SPEC)
Deprecated alias for "is_module_spec".
check_module_spec(PREFIX, SPEC)
Check whether *SPEC* is valid input for "compose_module_name".
Return normally if it is, or "die" if it is not.
compose_module_name(PREFIX, SPEC)
This function is intended to make it more convenient for a user to
specify a Perl module name at runtime. Users have greater need for
abbreviations and context-sensitivity than programmers, and Perl
module names get a little unwieldy. *SPEC* is what the user
specifies, and this function translates it into a module name in
standard form, which it returns.
*SPEC* has syntax approximately that of a standard module name: it
should consist of one or more name segments, each of which consists
of one or more identifier characters. However, "/" is permitted as a
separator, in addition to the standard "::". The two separators are
entirely interchangeable.
Additionally, if *PREFIX* is not "undef" then it must be a module
name in standard form, and it is prefixed to the user-specified
name. The user can inhibit the prefix addition by starting *SPEC*
with a separator (either "/" or "::").
BUGS
On Perl versions 5.7.2 to 5.8.8, if "require" is overridden by the
"CORE::GLOBAL" mechanism, it is likely to break the heuristics used by
"use_package_optimistically", making it signal an error for a missing
module rather than assume that it was already loaded. From Perl 5.8.9
onward, and on 5.7.1 and earlier, this module can avoid being confused
by such an override. On the affected versions, a "require" override
might be installed by Lexical::SealRequireHints, if something requires
its bugfix but for some reason its XS implementation isn't available.
SEE ALSO
* Lexical::SealRequireHints
* base
* "require" in perlfunc
* "use" in perlfunc
AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT
Copyright (C) 2004, 2006, 2007, 2009, 2010, 2011, 2012, 2014, 2017
Andrew Main (Zefram) <zefram@fysh.org>
Copyright (C) 2025 Graham Knop <haarg@haarg.org>
LICENSE
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.