if ( -d ) question

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

Dear Monks,
Why in this case if( -d $_ ) does not detect a directory

opendir(DIR, $mydir);
my @files = readdir(DIR);
closedir(DIR);

foreach (@files)
{
    next if( -d $_ );
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And when I indicate $mydir."/$_" it does ?

opendir(DIR, $mydir);
my @files = readdir(DIR);
closedir(DIR);

foreach (@files)
{
    next if( -d $mydir."/$_" );
[download]

Comment on if ( -d ) question Select or Download Code

Replies are listed 'Best First'.
Re: if ( -d ) question by kennethk (Abbot) on Mar 15, 2011 at 15:48 UTC
As it specifies in -X, `-d` and its brethren act relative to the current working directory. If `$mydir` is not ".", then you have the wrong file list. By specifying `$mydir."/$_"` (or `"$mydir/$_"`), you are giving a full path. You can also swap your current working directory with chdir, but that may have side effects you are not expecting.	[reply] [d/l] [select]
Re: if ( -d ) question by Corion (Patriarch) on Mar 15, 2011 at 15:45 UTC
Because `"$_"` and `"$mydir/$_"` are two different things? It's unclear to me what different outcome you expect. Should `-d "foo"` be true if anywhere on the filesystem there exists a directory with a name of `"foo"`?	[reply] [d/l] [select]
Re: if ( -d ) question by Anonymous Monk on Mar 15, 2011 at 18:08 UTC
It is always a wise idea to create a fully-qualified file name for use in all such tests. There are portable CPAN modules that can help you with doing that. When you are testing to see if a thing exists, it is critical that you are precisely sure what (Perl thinks...) you are actually looking for. It is terribly easy to destroy a priceless Ming vase...	[reply]