if - perldoc.perl.org

Perl Programming Documentation
Download Perl
Explore

Manual

- Overview
- Tutorials
- FAQs
- History / Changes
- License

Reference

- Language
- Functions
- Operators
- Special Variables
- Pragmas
- Utilities
- Internals
- Platform Specific

Modules

- A • B • C • D • E
- F • G • H • I • L
- M • N • O • P • S
- T • U • X

Tools

- Preferences

# if

Perl 5 version 26.0 documentation
Go to top
Show page index • Show recent pages
Recently read

# if

- NAME
- SYNOPSIS
- DESCRIPTION
  - EXAMPLES
- BUGS
- SEE ALSO
- AUTHOR
- COPYRIGHT AND LICENCE

# NAME

if - `use` a Perl module if a condition holds (also can `no` a module)

# SYNOPSIS

      use if CONDITION, MODULE => ARGUMENTS;  no if CONDITION, MODULE => ARGUMENTS;

# DESCRIPTION

The `if` module is used to conditionally load or unload another module. The construct

      use if CONDITION, MODULE => ARGUMENTS;

will load MODULE only if CONDITION evaluates to true. The above statement has no effect unless `CONDITION` is true. If the CONDITION does evaluate to true, then the above line has the same effect as:

      use MODULE ARGUMENTS;

The use of `=>` above provides necessary quoting of `MODULE` . If you don't use the fat comma (eg you don't have any ARGUMENTS), then you'll need to quote the MODULE.

## EXAMPLES

The following line is taken from the testsuite for File::Map:

      use if $^O ne 'MSWin32', POSIX => qw/setlocale LC_ALL/;

If run on any operating system other than Windows, this will import the functions `setlocale` and `LC_ALL` from POSIX. On Windows it does nothing.

The following is used to deprecate core modules beyond a certain version of Perl:

      use if $] > 5.016, 'deprecate';

This line is taken from Text::Soundex 3.04, and marks it as deprecated beyond Perl 5.16. If you `use Text::Soundex` in Perl 5.18, for example, and you have used warnings, then you'll get a warning message (the deprecate module looks to see whether the calling module was `use`'d from a core library directory, and if so, generates a warning), unless you've installed a more recent version of Text::Soundex from CPAN.

You can also specify to NOT use something:

     no if $] ge 5.021_006, warnings => "locale";

This warning category was added in the specified Perl version (a development release). Without the `'if'` , trying to use it in an earlier release would generate an unknown warning category error.

# BUGS

The current implementation does not allow specification of the required version of the module.

# SEE ALSO

Module::Requires can be used to conditionally load one or modules, with constraints based on the version of the module. Unlike `if` though, Module::Requires is not a core module.

Module::Load::Conditional provides a number of functions you can use to query what modules are available, and then load one or more of them at runtime.

provide can be used to select one of several possible modules to load, based on what version of Perl is running.

# AUTHOR

Ilya Zakharevich mailto:ilyaz@cpan.org.

# COPYRIGHT AND LICENCE

This software is copyright (c) 2002 by Ilya Zakharevich.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

Page index

- NAME
- SYNOPSIS
- DESCRIPTION
  - EXAMPLES
- BUGS
- SEE ALSO
- AUTHOR
- COPYRIGHT AND LICENCE