It means your Perl is ancient and doesn't support the default second argument. Use 
my ($memID) = unpack '@12A6', $_;

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instead.

Update: The change happened in 5.10 (2007), see Miscellaneous.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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In reply to Re^3: Strings overwrite themselves in print command by choroba
in thread Strings overwrite themselves in print command by tdsny71

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