Include the reason of error by use of $! variable ...

  open ... or die "Death is here because: $!.";
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Mind that readdir gives a file name below the directory being read from (relative path). You may need to supply the parent directory as appropriate to form correct path of file to be (found &) opened.

readdir(D) gives only the file names, if you included the $! in the file open function it could have given you the "oops No such file or directory" error message, in the file open function give the absolute path to open the file.

Here is the code I checked.

my $handle=$ARGV[0];

opendir(D,$handle) or die "cannot open $!";

my @files=readdir(D);

print "@files\n";

foreach my $file(@files)
{
        open (MYFILE,"$handle/$file") or die "oops $!";
        while(<MYFILE>)
        {
                print $_;
        }
}
closedir(D);
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readdir gives not only the file names but also the directory names present inside your $handle.

open (IN, "$handle/$file") on a directory will give you an error of course ;-)

you will have to test $file for being a file before opening it.

A directory is also a file.

You sure do love your warnings ...

#!usr/bin/perl -w
 use strict;
 use warnings;
...
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Next step would be the upgrade to being fatal ...

use warnings FATAL => 'all';
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But, there is more: fatal warnings are a ticking time bomb (via chromatic), and elsewhere around these parts.

G'day garny,

Welcome to the monastery.

The following repeats some of the information you've already been given. I've expanded on most of this because you say "I am a noob to perl" and you might as well get into good habits from the outset.

'die "cannot open"' and 'die"oops"' are poor error messages that convey little information. I find the autodie pragma is the easiest option; however, if you wish to hand-craft your error messages, do so in a useful fashion (e.g. 'die "Can't open $file for reading: $!"').

Unless you have a good reason not to, use lexical filehandles and directoryhandles (see examples in open and readdir respectively). Package variables (e.g. D and MYFILE in your posted code) are slower to access than lexical variables and you can't control their scope the way you can with lexical variables: in a tiny script, such as you have here, those reasons probably won't matter much, if at all; when you start writing more complex code, you may find this will save you debugging headaches (a good reason to avoid package variables even if the speed factor is negligible).

Get into the habit of using the 3-argument form of open: the documentation has details.

Close handles when you've finished with them; don't leave this until the end of your script. In the code your posted, the closedir() statement could have been placed immedaitely after the readdir() statement.

As explained in the readdir documentation, this function returns directory entries. While this will include the types of files you're intending to read (source code, config files, etc.), it will also include directories (at least the current, '.', and parent '..', directories) as well as symbolic links, character and block special files and so on: you can use the file test operators to filter the type(s) you want.

Instead of using

my @files = readdir($dirhandle);
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which returns just the names of all the files, directories, etc., you can use

my @files = grep { -f } map { "$dir/$_" } readdir($dirhandle);
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which returns the pathnames of just the files you want.

[Also consider File::Spec for a more portable solution for "$dir/$_".]

my @files = grep { -f } map { "$dir/$_" } readdir($dirhandle);
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To combat the excessive grepping & mapping going on above ...

my @files = map { -f $_ ?"$dir/$_" : () } readdir( $dirhandle ) ;
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I'd hardly consider one grep and one map to be "excessive grepping & mapping" nor something that one would need to "combat".

However, should you prefer the style you've posted, "-f $_" suffers from the problem already pointed out four times in this thread.

You could employ excessive usage of "$dir/$_", though. :-)

-- Ken

readdir is the devil, use Path::Tiny, it throws "exceptions" like autodie

use Path::Tiny qw/ path /;
my @files = path( $dirpath )->realpath->children();
for my $file( @files ){
    my $fh = path( $file )->openr_raw;
    while( <$fh> ){
        ...
    }
}
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