Question

With perl -e '$string="a";print ++$string;' we get b,

but with perl -e '$string="b";print --$string;' we get -1.

So, if we can increment why can’t we decrement?

EDITED
“The auto-decrement operator is not magical” by perlop

Perl give us lots of facilities, why not this one? This is not criticism, but wouldn’t be expected similar behavior for similar operators? Is there any special reason?

Answer 1

perlop(1) explains that this is true, but doesn’t give a rationale:

The auto-increment operator has a little extra builtin magic to it. [If applicable, and subject to certain constraints,] the increment is done as a string, preserving each character within its range, with carry[…]

The auto-decrement operator is not magical.

The reason you get -1 is because when interpreted as a number, “b” turns into 0 since it has no leading digits (Contrarily, “4b” turns into 4).