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Re: How to dig through symbol tables

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Ben Morrow
June 19, 2008 18:18
Re: How to dig through symbol tables
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> I'm trying to figure out the "right" way to dig through a
> program's symbol table without disrupting it.  According to the
> docs, "defined" only works for scalars and subs.  I would think
> that "defined *{FOO}{THING}" would work for everything, but it
> exhibits this annoying behavior:
>     $ perl -le 'sub x{};for (qw(SCALAR ARRAY HASH CODE IO)) { print
> "foo-thing $_" if defined *{x}{$_}; }'
>     foo-thing SCALAR
>     foo-thing CODE
> Indeed, if any other slot is defined, *{FOO}{SCALAR} seems to be
> defined.  Is this intended behavior?

Yes. If a glob exists at all it has a SCALAR slot.

> I am currently using *{FOO}{THING} for everything but scalars,
> and (afterwards) "defined $FOO" for scalars, but it seems like
> there should be a better way.

'defined $FOO' tells you whether the scalar contains undef or not, not
whether it exists. For instance

    our $FOO;
    defined $FOO;

returns false, even though $FOO exists. Basically, if any part of *FOO
exists, $FOO exists as well.


quine="echo 'eval \$quine' >> \$0; echo quined"
eval $quine
#                                                        []

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