That is a a great description of what is going on, but I think his
question centered on the &SYNTAX*, not the *SEMANTICS*. As a
programmer from the "algebraic" school (FORTRAN, algol, pascal, C,
Ada, etc.), he is unacustomed to seeing a function call without
surrounding parens. The key concept here, and one that is rather
"perly", is "list context" and "scalar context".
James Edward Gray II writes:
> On Dec 8, 2003, at 10:52 AM, [EMAIL PROTECTED] wrote:
>
> > I've just started trying to pick up a little perl.
> > I'm breezing through "Learning Perl" and reading the perl docs.
> >
> > Here is some syntax I found a little funny, and I was hoping somebody
> > could explain this too me:
> >
> > opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
> > @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
> > closedir DIR;
> >
> > The first and 3rd lines I have no problem with.
> >
> > Its that line with the grep in it.
>
> Okay, let's go step by step readdir() is called (in list context), so
> it returns all entries in the directory. Simple enough.
>
> That returned list is immediately fed to another built-in, grep().
> grep() goes through every element in the list, checking it against some
> expression you provide (the part in the braces). Inside the
> expression, the element you're currently checking is in Perl's default
> variable $_. If the expression returns true for that element, it is
> included in grep()'s return list. If not, it is omitted.
>
> In this case, the expression check two things. First, it uses a
> pattern match on the name to see if it begins with a dot (.). If it
> does, it checks to make sure the entry is a file, to rule out entries
> like '.' and '..'. If the entry passes both tests, grep() returns it.
> Otherwise, it's let out of the return list. It may help to think of
> grep() as a filtering engine you can use to build on-the-fly lists.
>
> Finally, the list returned by grep() is assigned to @dots, which is
> pretty much what it will contain, any file beginning with a dot (hidden
> files on a Unix system).
>
> Here's a rough English translation of the line:
>
> place in @dots all things beginning with . that are actually files from
> the listing for DIR
>
> Hope that helps.
>
> James
>
>
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