The answer from Abigail-II above is correct. In case you're wondering what an "openddir/readdir wrapper" is, it's a loop like this:

chdir $the_directory
    or die "Couldn't chdir to $the_directory: $!";
opendir(D, ".")
    or die "Couldn't open . ($the_directory): $!";
while ($file = readdir D)
{
    next unless $file =~ /\.las$/;
    # other logic later...
}
closedir D;
[download]

Another common idiom is to use grep to pull out the entries you want first, although this will consume memory proportional to the number of files and the lengths of their names.

chdir $the_directory
    or die "Couldn't chdir to $the_directory: $!";
opendir(D, ".")
    or die "Couldn't open . ($the_directory): $!";
my @files = grep { /\.las$/ } readdir D;
closedir D;
foreach my $file (@files)
{
    # whatever...
}
[download]

Note, both of those code samples are untested.

HTH