You already got a good clue: $^O is the perl special variable containing the OS, from the perl point of view. But with perl you have many many options to finely leverage the platform/architecture checking.

1) $^O being your first option: you can use it in if construct: if ($^O eq 'MSWin32 ) { ...' or in a dispatch thable:

my %clear_command = ( MSWin32 => 'cls', Linux => 'clear' ... );

system (1, $clear_command{ $^O }  );
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As said in perlvar concerning $^O on windows it always returns MSWin32 but using Win32 module you have something better:

print Win32::GetOSName(),Win32::GetOSVersion();

# output:
Win10Business (64-bit)100179362002561
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2) Config is a core module that holds ~900 values concerning the current perl installation: for example the architecture:

print $Config{archname}; # MSWin32-x64-multi-thread or if current perl is configured to use threads: $Config{usethreads} The module populates for you a readonly hash named %Config

3) the if module (not the normal if ) is useful to import the rigth module depending on situation: if you need to work with the OS name (given the above) you may need Win32 module to get the right name:  use if $^O eq 'MSWin32', 'MSWin32'; # note that it wants module in a string!

4) in perlvar look also at $] and $^V useful to inspect the current perl version (versions are a bit.. confusing in perl: recent history shows.. ;)

5) last but not least consider that many modules do their best in being agnostinc in respect of the operating system: come to mind Term::ReadLine that works fine on different platforms. Under the hood the module will load the appropriate module dependin on platforms: Term::ReadLine::Linux for example if run on Linux.

The very same does the best module for portable program: the core module File::Spec that abstracts many important file and path related operations being very OS agnostic

6) a look at perlport is recomended

good luck!

L*

PS (the title was: Perl Newbie question) next times try to choose more meaning titles for your questions: it wil be useful for future searcher!