Why don't you read the directory entries with internal Perl functions, instead of relying on some external program (OLDTTGW principle):

Fill_List( '/dir', '^error' );

sub Fill_List {
  my $dir   = shift;
  my $match = shift;
  my @found;
  opendir DIR, $dir or die "Cannot open directory $dir: $!"\n;
  while( defined( my $file = readdir(DIR) )) {
    push @found, $file if $file =~ /$match/o;
  }
  close DIR;
  return @found;
}
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Note that I am returning the values in an array. It is better to have a routine do one thing, and one thing only. If you want to write the contents out to a file, do that in another routine. Prepare for (obvious) future uses the code could be put to.

Your code has a few style issues that leap out at me:

• You're not using lexical (my) variables, so you're probably not using strict. Until you know why and when it's ok not to use it, you should use strict;
• file handles (list and infile in your example) by convention are always in uppercase;
• if you are not interpolating Perl variables into strings or using meta characters like \n and \t, use 'single quotes' instead of "double quotes";
• and if you are not diddling with subroutine parameter lists, do not use the &func() way of calling function, drop the ampersand. If you don't know what diddling with subroutine parameter lists means, then just avoid using & on subroutine calls.

update: oops, re-reading my code makes me realise this code will only work correctly the first time it is called, due to the /o modifier on the regexp. (It will just keep on returning files that match what the first call was asked to match. The correct method would be to use the qr// operator if the version of Perl supports that. Just put $match = qr/$match/; before the while loop. Otherwise, for earlier versions, one would have to build the loop up in a string, and eval that, which is downright icky.

--

g r i n d e r
just another bofh

print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u';