Module name syntax¶

The usable module name syntax has not changed from Perl 5.000 up to Perl 5.15.7. The syntax is composed entirely of ASCII characters. From Perl 5.6 onwards 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. This may finally be addressed in the Perl 5.17 series.

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.

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 signalled. That's the optimistic bit.

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 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 "::").