You need to quote the command as well if it contains spaces. ie. This will work as. The inner, backslash-escaped quotes will be passed to the shell.

my $ret = system( "\"D:\\Program Files\\bin\\t.pl\"" );
[download]

However, rather than having to escape the inner quotes and double the backslashes, it's easier to make use of perls profusion of quoting operators.

my $ret = system( q[ "D:\Program Files\bin\t.pl" ]);
[download]

or

my $ret = system( '"D:\Program Files\bin\t.pl"' );
[download]

As an example

P:\test>copy con "d:\program files\test.pl8"
print "Hi there! from $0";
^Z
        1 file(s) copied.


P:\test>perl
system( '"d:\program files\test.pl8"' ) and warn 'Failed with: ', $?;
^Z
Hi there! from D:\program files\test.pl8
P:\test>
[download]

Hope that clarifies things a bit.