[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.
> grep is obviously a built-in perl function.
>
> This is something I've seen before ...
> the output of the function readdir is "trickling down" to become the
> input of the function grep ?
>
> In C or Java you would write
> grep(readdir(DIR)) most likely ?
>
> If that is so, what is all that business with the curly braces ?
> I thought curly braces are supposed to denote code sections ?
Yes, exactly, the curly braces allow the use of a code block instead of
a simple expression. Having a code block means that you can have
multiple statements and lexical variables.
> So, it's like the output of readdir is "trickling" through the curly
> braces and then the output after this is "trickling" through grep ?
grep acts like a filter. grep's expression determines whether an
element from the right hand list will be passed through to the left.
> If so, what is the "input" to the code section in the curly braces ?
grep aliases the variable $_ to the current element of the list on the
right hand side.
> Anyhow, all this is a bit weird to me, so I was hoping someone could
> shed some light on it.
Have you read the documentation for grep in perlfunc.pod?
> p.s. It seems some of my confusion comes from the fact that I am used to
> putting () around funtion calls.
perldoc perlfunc
[snip]
Any function in the list below may be used either with or
without parentheses around its arguments. (The syntax
descriptions omit the parentheses.) If you use the paren
theses, the simple (but occasionally surprising) rule is
this: It looks like a function, therefore it is a func
tion, and precedence doesn't matter. Otherwise it's a
list operator or unary operator, and precedence does mat
ter. And whitespace between the function and left paren
thesis doesn't count--so you need to be careful sometimes:
> That still doesn't help with the curly braces though ... %^)
They can (IIRC) be used in four different ways: { code block }, $hash{
element }, ${'variable name'} and /match count{4,7}/.
John
--
use Perl;
program
fulfillment
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