Shell Programming and Scripting

#!/usr/bin/perl
chomp(@files=`ls *.dat`);
for $i (@files){
  open I, "$i";
  $l=$m=$h=0;
  while ($n=<I>){
    chomp $n;
    $l++ if $n<=2;
    $m++ if $n>2 && $n<=3;
    $h++ if $n>3;
  } 
  print "$i: low (2>) - $l ; medium (3> and 2<) - $m ; high (3<) - $h\n";
}

$ cat script.pl
use warnings;
use strict;

die "Usage: perl $0 low-range medium-range high-range files\n" unless 
    @ARGV >= 4 and
    grep { /^-?\d+$/ } @ARGV[0..2] and    # Integer ranges.
    defined $ARGV[3];                    # At least one file.

my %range = (
    low_limit => shift,
    medium_limit => shift,
    high_limit => shift
);


while ( <> ) {
    ## Only count lines without number.
    if ( /^\s*\d+(?:\.\d*)\s*$/ ) {
        if ( $_ < $range{ low_limit } ) {
            $range{ low_num }++;    
        } elsif ( $_ >= $range{ low_limit } && $_ < $range{ medium_limit } ) {
            $range { medium_num }++;
        } elsif ( $_ >= $range{ high_limit } ) {
            $range{ high_num }++;
        }
    }

    ## Print result in end of each file.
    if ( eof ) {
        printf 
            "%s: low (%d<) - %d ; medium (>%d and %d<) - %d ; high (>%d) - %d\n", 
            $ARGV,
            $range{ low_limit },
            $range{ low_num } || 0,
            $range{ low_limit },
            $range{ medium_limit },
            $range{ medium_num } || 0,
            $range{ high_limit },
            $range{ high_num } || 0,
            delete @range{ qw(low_num medium_num high_num) }; 
    }
}
$ perl script.pl
Usage: perl script.pl low-range medium-range high-range files
$ perl script.pl 2 3 3 *.dat  # Output with my test files.
1.dat: low (2<) - 4 ; medium (>2 and 3<) - 1 ; high (>3) - 1
2.dat: low (2<) - 2 ; medium (>2 and 3<) - 1 ; high (>3) - 3