It's like making explicit the implicit '+' that precedes any non-negative number (think scalar ::= number or string).

Do you remember, when learning how to format numbers for output (using '%f', '%g', etc.) with printf in C, you had to account for the sign position? It would display as either a hyphen or blank. A blank, however, was analagous to a plus-sign.

Likewise, on input, non-negative numbers could optionally be expressed with a leading plus-sign. Since scalars (or scalar expressions) may be either numbers or a strings in perl, perl allows this with arbitrary scalar expressions.

dmm

You can give a man a fish and feed him for a day ...
Or, you can teach him to fish and feed him for a lifetime

More examples of unary plus:

print (3-1)*2;      # oops!  print (...) interpreted as function ...
print +(3-1)*2;

sub foo { $foo }
$h{foo};            # equivalent to $h{'foo'}
$h{+foo};           # but maybe you meant $h{foo()}
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