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Postings from June 2008
Quoth sorourke@ucsd.edu:
> 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.
Ben
--
#!/bin/sh
quine="echo 'eval \$quine' >> \$0; echo quined"
eval $quine
# [ben@morrow.me.uk]
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