1. Looks safe because it looks like a comment is being evaluated, but what if $nada contained a newline? If text is being inserted in to code without first being converted into code, you have a code injection bug.

2. [See (6) first] _ refers to *_, the glob (symbol table entry) that contains $_, @_, etc. Here, it's used as a file handle, presumably populated by an earlier stat or -X operator.

3. s/// returns true if it matched, so this code repeatedly performs the substitution until it doesn't match. This pattern is usually buggy. Replacing the whole with a single s///eg will solve these bugs.

4. [See (6) first] Creates a lexical variable named $a and aliases $_ to it until the end of the current lexical scope. Note that creating a lexical named $a will cause problems for sort and similar functions.

5. $h{$i, $j, ...} is equivalent to $h{join($;, $i, $j, ...)}.

6. *name is a typeglob, or just glob for short. Globs are used as the entries of the symbol table, so a glob is a struct with a slot for each type of variable (scalar, array, hash, glob, code) and few others (file handle, directory handle, format). I could be missing some. One might say it's a bunch of variables of different types, perhaps even a glob of types... Globs are weird because they are both a type of variable (e.g. *foo) and a type of scalar (e.g. $foo = *foo;).

Update: Added missing answer for (6).

1): Aha - it's a fallback. Full code from File::Find:

# check whether or not a scalar variable is tainted
# (code straight from the Camel, 3rd ed., page 561)
sub is_tainted_pp {
    my $arg = shift;
    my $nada = substr( $arg, 0, 0 );    # zero-length
    local $@;
    eval { eval "# $nada" };
    return length($@) != 0;
}

# We need a function that checks if a scalar is tainted. 
# Either use the # Scalar::Util module's tainted() function 
# or our (slower) pure Perl
# fallback is_tainted_pp()
{
    local $@;
    eval { require Scalar::Util };
    *is_tainted = $@ ? \&is_tainted_pp : \&Scalar::Util::tainted;
}
[download]

And i'm banging my head against a wall to understand it. This code mucked my day ;-)

Best regards, Karl

This is a Perl typeglob: see Typeglobs on perldata

Typeglobs are the internal data of which the symbol table is filled. Hic sunt leones .. here black magic begins..

See also many links on my homenode

L*

6.) Typeglob

Combine ppi_dumper with Perl documentation / Modern Perl and super search/Tutorials...

PPI::Document
  PPI::Token::Whitespace        '\n'
  PPI::Statement
    PPI::Token::Symbol          '*foo'
  PPI::Token::Whitespace        '\n'

So PPI::Token::Symbol says: The PPI::Token::Symbol class is used to cover all tokens that represent variables and other things that start with a sigil.

So perltoc or perl -> perldata - Perl data types -> http://perldoc.perl.org/perldata.html#Typeglobs-and-Filehandles

Would it be easier if PPI::Token::Symbol linked perldata all on its own? Yes :D