#!/usr/bin/perl 
 
if ($#ARGV != 5) 
{ 
  die "Usage x0_amber traj_name frame1 frame2 r0 r1 dr\n"; 
} 
 
$traj=$ARGV[0]; 
$frame1=$ARGV[1]; 
$frame2=$ARGV[2]; 
$r0=$ARGV[3]; 
$r1=$ARGV[4]; 
$dr=$ARGV[5]; 
print "frame $frame1-$frame2\n"; 
 
$no_frm=$frame2-$frame1+1; 
for($r=$r0;$r<=$r1;$r=$r+$dr) 
{ 
  foreach $i($frame1..$frame2) 
  { 
    open(PDB,"$traj.$i"); 
    @line_pdb=<PDB>; 
    close PDB; 
    for ($j=0;$j<=$#line_pdb;$j++) 
    { 
        #calculation skipping 
        print ..... 
    } 
  } 
  $x0=$n_count/$no_frm; 
  print "$r    $x0\n"; 
}

$|++;