$FileToOpen=myfile.xlsx;

##</code><code>##

$ perl -e '$FileToOpen=myfile.xlsx;'
$ 

##</code><code>##

$ perl -we '$FileToOpen=myfile.xlsx;'
Unquoted string "myfile" may clash with future reserved word at -e line 1.
Unquoted string "xlsx" may clash with future reserved word at -e line 1.
Name "main::FileToOpen" used only once: possible typo at -e line 1.

##</code><code>##

$ perl -Mstrict -e '$FileToOpen=myfile.xlsx;'
Global symbol "$FileToOpen" requires explicit package name (did you forget to declare "my $FileToOpen"?) at -e line 1.
Bareword "myfile" not allowed while "strict subs" in use at -e line 1.
Bareword "xlsx" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.

##</code><code>##

$ perl -MO=Deparse -e '$FileToOpen=myfile.xlsx;'
$FileToOpen = 'myfilexlsx';
-e syntax OK

##</code><code>##

use strict;
use warnings;