in reply to File ext number

Your match doesn't match when readdir returns ., so $1's value isn't changed by the match, and it was previously undefined. 

use strict;
use warnings;

my %ext;
opendir my $dh, './' or die $!;
for (grep { -f } readdir $dh) {
   ++$ext{$1} if /\.([^.]+)$/;
}

print "$_ - $ext{$_}\n" for keys %ext;

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Alternate: 

use strict;
use warnings;

my %ext;
opendir my $dh, './' or die $!;
++$ext{$1} for map { -f && /\.([^.]+)$/ ? $1 : () } readdir $dh;

print "$_ - $ext{$_}\n" for keys %ext;

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Re^2: File ext number
by toolic (Bishop) on Mar 19, 2010 at 23:38 UTC
    Your match doesn't match when readdir returns .
    Are you saying that the dot (.) directory somehow makes it past the grep {-f} filter in the OP's code? I freely admit I have no idea what that whole line does in the OP's code, but it would be surprising to me if . made it past the filter.
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      Are you saying that the dot (.) directory somehow makes it past the grep {-f} filter in the OP's code?

      I guess I was without realizing it. Obviously, that's not true and my explanation is wrong. Take two: 

      $ext{$1} += (m/([^.]+)$/);

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      means something close to 
      $ext{$1} = $ext{$1} + (m/([^.]+)$/);

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      Well, actually more like the following, but it doesn't matter for this discussion: 

      alias $temp = $ext{$1};
$temp = $temp + (m/([^.]+)$/);

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      Either way, you are relying on Perl evaluating the RHS of the "+=" operator before its LHS, and that's not how Perl operates. In fact, Perl doesn't document how it operates in this circumstance, and that's the reason it's generally a no-no to change and use the same variable in the same expression.

      Even though my earlier explanation was wrong, the solutions I posted still avoid the problem.

      Update: Improved phrasing by inlining footnotes.

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