foreach and opendir differences

dobby has asked for the wisdom of the Perl Monks concerning the following question:

I'm writing my first ever script to delete non numeric files from various directories and I'm not too sure which way I should get the file names.
I have got a foreach loop working but it doesn't list the . files. My opendir does list the files though.
My O'Reilly Learning Perl doesn't have an explanation that I can find.
Is my opendir use better or more efficient etc that the foreach command?
Do I have to do multiple foreach's and include a (</xxx/*>) or (</xxx/.*>)>.
I have included my test script as well (it even works!).

#!/usr/bin/perl -w
use strict;
use diagnostics;
my @dirvar="";
my $foreachvar="";

opendir(DIRHAN,"/xxx");
@dirvar = readdir(DIRHAN);
print "@dirvar\n";
closedir(DIRHAN);

foreach $foreachvar (</xxx/*>)
   { if (-f $foreachvar) {print "$foreachvar \n" } }
[download]

Many Thanks,
Dobby
P.S. sory about the format, I'm trying to get to grips with this <code><br> stuff. Its HTML isn't it?

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Re: foreach and opendir differences by Tanktalus (Canon) on Apr 07, 2005 at 03:49 UTC
It's not actually a foreach problem. `my @dirvar = </xxx/> print join ':', @dirvar;` [download] It's a glob problem. Which reminds me - I recommend avoiding the `<...>` operator for that. Not just because it's a pain to type and get to display properly here ;-), but because using "glob" is so much more obvious as to what you're doing. (`<...>` is implemented in terms of glob, so this doesn't change anything functionally) `my @dirvar = glob "/xxx/";` [download] Looking up glob in the perlfunc documentation (e.g., "perldoc -f glob"), you see it is implemented via File::Glob. Looking that up, you see it tries to implement C shell semantics. This sets off warning bells: on unix, files with a leading dot are considered "hidden" and should not be shown by default. So "" does not match leading dots. Other dots, but not leading dots. Looking C shell up (I'm a Korn shell/Bourne-again shell type of guy m'self), I see that this should work: `my @dirvar = glob "/xxx/{.,}";` [download] The reason? Braces denote choices, all of which apply. The comma separates the choices. So this expands to both "/xxx/." and "/xxx/" simultaneously, in a single call. readdir, by the way, does not use shell semantics, and thus ignores "hidden" attributes, laying everything out for you. HTH	[reply] [d/l] [select]
Re: foreach and opendir differences by jpeg (Chaplain) on Apr 07, 2005 at 04:09 UTC
It's the difference between shell expansion using * and ..., well, readdir. perldoc perlop, perldoc -f glob, and perldoc File::Glob has a lot of info about <> and its many behaviors. As you're using it with foreach, you're globing in list context, using glob behavior as per a /bin/csh. I poked through man csh a bit, but can't find a documented reason why an asterisk would ignore dotfiles. When I'm in csh and bash, a ls /dir/* also ignores dotfiles, so I guess it's working as expected. readdir, on the other hand, probably uses the readdir system call, documented in man 3 readdir. It actually reads the directory as a file, which is a list of inodes and always contains . and .. as entries. As far as the code tags... no idea. there's probably some page with instructions for writeups we should have read somewhere. I just lurked for a bit and copied people ;)	[reply]
Re: foreach and opendir differences by dobby (Initiate) on Apr 07, 2005 at 04:25 UTC
Is there a preference or a best practice or doesn't it matter. I know I can do it as a one liner from a system call but I want to learn bad habits. Dobby.	[reply]
Re^2: foreach and opendir differences by willyyam (Priest) on Apr 07, 2005 at 10:52 UTC
...but I want to learn bad habits Wow, so many to choose from. Smoking, not using `strict`, leapfrogging unicorns (bad, but not always practical - substitute rhinos if unicorns are unavailable) not wearing pants to work... I think bad habits are called that for a reason, but hey, do what you need to do.	[reply] [d/l]