$var =~ s/$lhs/$rhs/ee;

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means 
$var =~ s/$lhs/eval $rhs/e;

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(Except that exceptions aren't caught.)

That means $rhs must contain valid Perl code, yet $1$2$3 is not valid Perl code. "$1$2$3" or $1.$2.$3 would be valid Perl code, so you want 

$rhs = '"$1$2$3"';

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or 
$rhs = '$1.$2.$3';

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In reply to Re: "ee" in Regular Expression: version issue? by ikegami
in thread "ee" in Regular Expression: version issue? by Anonymous Monk

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