Shell Programming and Scripting

#!/usr/bin/perl
#This script is to pick the specific fields from a files starting from a specific row
# FILE -> Name of the file to be pasd at runtime.
# rn -> Number of the row from where the data has to be picked.
use strict;
use warnings;
my $file = shift || "FILE";
my $rn = shift;
my $cols = shift;
open( my $fh, "<", $file) or die "Could not open file '$file' : $!\n";
while (<$fh>) {
    $. <= $rn and next;
    my @fields = split(/\t/);
    print "$fields[$cols]\n";
}

0, 1, 3..6, 21..33

perl extract.pl FILE 3 0, 1, 3..6, 21..33

perl extract.pl 3 0,1,3..6,21..33

perl extract.pl 3 0, 1, 3..6, 21..33

perl extract.pl FILE 3 0, 1, 3..6, 21..33

perl extract.pl FILE 3 0, 1, 3..6, 21..33

my $cols = shift;

perl extract.pl FILE 3 "0, 1, 3..6, 21..33"

#!/usr/bin/perl
#This script is to pick the specific fields from a files starting from a specific row
# FILE -> Name of the file to be pasd at runtime.
# rn -> Number of the row from where the data has to be picked.
use strict;
use warnings;
my $file = shift || "FILE";
my $rn   = shift;
my $cols = shift;
open( my $fh, "<", $file ) or die "Could not open file '$file' : $!\n";
print "debug, reading columns :$cols: from $file at line $rn\n";

while (<$fh>) {
  $. <= $rn and next;
  my @fields = split(/\t/);
  # print "$fields[$cols]\n"; #Fails, need @, not $
  # print "@fields[0, 1, 3..6]\n"; #OK
  # print "@fields[0, 3]\n"; #OK
  # print "@fields[0,1,3..6,7]\n"; #OK
  # print @fields[$cols],"\n"; #Fails
  print join( "\t", @fields[ eval($cols) ] ), "\n";    #OK
}