Ovid, this is behaviour appears in 5.6.1.

% perl -v
This is perl, v5.6.0 built for i386-openbsd 
[...]
% perl -lwe 'print q{foo@bar.com}'
foo@bar.com
% perl -lwe 'print qq{foo@bar.com}'
In string, @bar now must be written as \@bar at -e line 1, near "foo@b
+ar"
Execution of -e aborted due to compilation errors. 

  --versus--

% perl -v
This is perl, v5.6.1 built for i686-linux  
% perl -lwe 'print q{foo@bar.com}'
foo@bar.com
% perl -lwe 'print qq{foo@bar.com}'
Possible unintended interpolation of @bar in string at -e line 1.
Name "main::bar" used only once: possible typo at -e line 1.
foo.com
[download]

The error messages change when you use strict, of course, but you get the idea. By the way, if you have the time, upgrading to 5.6.1 is recommended. There are a lot of POD tweaks, test tweaks, leak removals, B::* improvements and all sort of assorted corrections between the two.

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