[EMAIL PROTECTED] wrote:
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.
The first line is better written as
opendir(DIR, $some_dir) or die "can't opendir $some_dir: $!";
Note the use of 'or' instead of '||'. Precedence is extremely important,
especially in perl where so much of the code can be "short-circuited".
Changing the || to or in the above line has no effect. However, as Jeff said, parens in Perl are often optional on subroutine calls and if we leave those out:
opendir DIR, $some_dir or die "can't opendir $some_dir: $!";
We get the traditional Perl open() call and here it matters if we use || or or. Why do we write it like that? We like the way it reads.
Its that line with the grep in it. grep is obviously a built-in perl function.
This is something I've seen before ... the output of the function readdir is "trickling down" to become the input of the function grep ?
One minor problem, there is a comma missing before the 'readdir':
@dots = grep { /^\./ && -f "$some_dir/$_" }, readdir(DIR);
The line compiles fine. The block version of grep() does not require a comma.
perldoc -f grep
No, you would use a while or for loop and then search for files not beginning
with a dot.
So while-readdir, search for files (only) and test if they DONT begin with a dot, then store them into an array. Now that we have the
You say this twice, but that still doesn't make it true. I think you need to reread that grep() call. ;) We're searching for files that DO begin with a dot here and placing them in the fitting @dots array.
If that is so, what is all that business with the curly braces ? I thought curly braces are supposed to denote code sections ?
This is correct, it's a "chunk of code". It will be executed once for each item returned by readdir().
p.s. It seems some of my confusion comes from the fact that I am used to
putting () around funtion calls. That still doesn't help with the curly
braces though ... %^)
Parens are often optional. When in doubt, use them. I never use them in
simple print statemtents, but some functions like 'split', it just makes more
sense.
I think the easiest rule to start learning with in use parens for your own subs and leave them off of built-ins, except when you need them to clarify/enforce precedence.
James
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