Check:

echo $PERL5LIB
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That's a shell, not a perl, command.

Someone possibly set this previously somewhere such as /etc/profile. If that is the problem, until you can figure where it is set — grep -R PERL5LIB /etc will help with that — just

export PERL5LIB=
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I.e., nothing after the equals sign. You could also add that to ~/.bashrc.