Use %ENV, or more specifically, $ENV{PATH}. 

$ENV{PATH} = join ';',
             'C:\\123',
             '"C:\\Program Files\\456"',
             $ENV{PATH};

[download]

or 

$ENV{PATH} = qq{C:\\123;"C:\\Program Files\\456";$ENV{PATH}};

[download]

This changes the PATH for the current process. Children later launched by this process inherit this modified PATH (unless measures are taken to prevent this).

Update: Improved example.

In reply to Re: How do you modify the Win32 PATH statement in a Perl script? by ikegami
in thread How do you modify the Win32 PATH statement in a Perl script? by MoonShadow

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