# Anything to the left of a 
# => is treated as like it's 'single quoted'
# That means variables are not interpolated.

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Variables are interpolated on the left of a =>. E.g. 

perl -MData::Dumper -le 
'$foo = "blah"; %a = ( $foo => 42 ); print Dumper \%a'
$VAR1 = {
          'blah' => 42
        };

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Hooray for DWIMery.

Update: Fixed formatting

In reply to Re^2: passing a variable as a string by friedo
in thread passing a variable as a string by coldfingertips

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