while ($file = <$dir\\*.txt>) {
  #do your stuff
}

##</code><code>##

opendir	( DIR, $dir ) 	 || die "Cannot open directory $dir: $!";
while ( defined( $file = readdir(DIR) ) ) {
  next if $file =~ /^\.\.?$/;  	
  if ( $file =~/txt$/ ) {
    #do your stuff
  }
}
closedir DIR;