... can't open device: \.\COM22 ...

Notice the leading single backslash in the error message where a double backslash was advised. Even in single quoted strings, backslash interpolation is tricky: 

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'A: \\.\COM22';
 print qq{'$s'};
 ;;
 $s = 'B: \\\.\COM22';
 print qq{'$s'};
"
'A: \.\COM22'
'B: \\.\COM22'

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In reply to Re^3: Serial communication between perl and arduino by AnomalousMonk
in thread Serial communication between perl and arduino by perl_sck_58

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