Shell Programming and Scripting

#!/usr/bin/perl




# open file
  open FILE, "OUTPUT";
  @file = <FILE>;
  close FILE;

 # scan file
  $stop = scalar(@file);
  for ($n_line = 0; $n_line <= $stop-1; $n_line++) {
  $line = $file[$n_line];

if ($line=~/trace\/3\s*(\d.\d+E\-\d+)/) {
$average_pressure=$1;
open result1, ">>../pressure.txt";
#print  "$average_pressure\n";
print result1 "$average_pressure\n";
close result1; 
}

if ($line=~/trace\/3\s*(\d.\d+E\+\d+)/) {
$latt_length=$1;
open result2, ">>../lattice_vector.txt";
#print  "$latt_length\n";
print result2 "$latt_length\n";
close result2; 
}

if ($line=~/Average cell vectors\s*r.m.s. fluctuations /) {
chomp($file[$n_line + 2]);
	@matrix_line1 = split(/ +/, $file[$n_line + 2]);
        chomp($file[$n_line + 3]);
        @matrix_line2 = split(/ +/, $file[$n_line + 3]);
        chomp($file[$n_line + 4]);
        @matrix_line3 = split(/ +/, $file[$n_line + 4]);
		open result2, ">>../lattice_vector_error.txt";
#print  "$matrix_line1[4]\n";
print result2 "$matrix_line1[4]\n";
close result2; 
}

if ($line=~/Average pressure tensor\s*r.m.s. fluctuations/) {
chomp($file[$n_line + 2]);
	@matrix_line1 = split(/ +/, $file[$n_line + 2]);
        chomp($file[$n_line + 3]);
        @matrix_line2 = split(/ +/, $file[$n_line + 3]);
        chomp($file[$n_line + 4]);
        @matrix_line3 = split(/ +/, $file[$n_line + 4]);
#print "@matrix_line1\n @matrix_line2\n @matrix_line3\n";
$pressure_error=($matrix_line1[4]+$matrix_line2[5]+$matrix_line3[6])/3;
#print "$pressure_error\n";
open result1, ">>../pressure_error.txt";
print result1 "$pressure_error\n";
close result1; 
}

}

@ARGV = get-list-of-files;
while (<>) {
  ....
}