Just to build on arturo's comment of using the ternary || operator: if you have (or plan to have) multiple arguments, then something along these lines might work better for you:

   my $date = @ARGV ? shift @ARGV : yesterday();
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That way you can easily inline other arguments:

   my $arg1 = @ARGV ? shift @ARGV : 'default value';
   my $date = @ARGV ? shift @ARGV : yesterday();
   my $arg2 = @ARGV ? shift @ARGV : 'other value';
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mr.nick ...