You need to change:

if($line =~ /Handling NSPAdvice for mechanism [4]/) {
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to

if($line =~ /Handling NSPAdvice for mechanism \[4\]/) {
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because the character [ is special in a regular expression.

Update: Your logic in the statement:

if ($errorCode != 0 || $errorCode != 1) {
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is flawed because an $errorCode with any number will pass this test.   You probably meant:

if ($errorCode != 0 && $errorCode != 1) {
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