use executes at compile time, before your if statement even gets evaluated. The result of that is that use DBI happens on all platforms, not just Linux.

Instead you need to load the module with require, a la:

if ($^O eq 'Linux') {
   require DBI;
}
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There's a module called if, which is part of the core Perl distribution. It wraps up the above pattern allowing you to use the somewhat neater:

use if ($^O eq 'Linux'), 'DBI';
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It's worth noting that this is not some kind of extension to Perl's syntax. You're simply useing the if module and passing its import method two parameters: the first is a boolean (the result of evaluating $^O eq 'Linux'); the second is a module name as a string. The if module then contains the logic to load the named module only if the boolean is true.

I search using your keywords

on perlmonks only  [based on os] based on os -> Splitting an extension based on OS

if , Devel::CheckOS

use if ($^O eq "MSWin32"), 'Win32::Process';
use if ($^O eq "MSWin32"), 'Win32::SearchPath';
use if ($^O ne "MSWin32"), 'POSIX';
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using DuckDuckGo  [ddg://site:perlmonks.org Include a package based on OS.] site:perlmonks.org Include a package based on OS. -> How can I include a module for Windows only??

Using Google  [google://site:perlmonks.org Include a package based on OS.] site:perlmonks.org Include a package based on OS. -> How can I include a module for Windows only??, including modules during runtime and dealing with OS specific (constants) code block, Splitting an extension based on OS

My memory Re: How do you use the if pragma? , Re^5: Problems with forking, Re^3: Loading a module at runtime, Re: mention a non-installed module in script, Re: constants wont optimize, Re^3: How to have OS specific code sections in Perl, Re: Variable as module name? (modern perl), Re^2: Redefining Imported Subs: of scope and no, use Module::Implementation

Perl::OSType

use Perl::OSType qw' is_os_type ';
use if is_os_type('Windows'), qw' Win32::SerialPort ';
use if not is_os_type('Windows'), qw' Device::SerialPort ';
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ssearch , its for everybody