On the other hand, using a greater-than always clobbers (truncates to zero length) an existing file, or creates a brand-new one if there isn't an old one. Adding a "+" for read-write doesn't affect whether it only works on existing files or always clobbers existing ones.

#!/usr/local/bin/perl
use strict;
use warnings;

open (my $sort_fh, '+<', 'C:\temp\SORT.CSV') or die "Cannot open file 
+$!\n";


    my @sorted = map {$_->[0]}
                 sort { $a->[6] cmp $b->[6] ||
                        $a->[2] cmp $b->[2] ||
                        $a->[5] cmp $b->[5] ||
                        $a->[9] <=> $b->[9]}
                 map {chomp;[$_,split(/,/)]} <$sort_fh>;

                   seek $sort_fh, 0, 0;
                   foreach(@sorted) {
                  printf $sort_fh "$_\n";
                  }
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Note in the above I've swapped to 3-argument open and lexical file handles. Technically unnecessary, but nice for avoid escaping problems on file names and not having to close file handles.

Sir, Please tell me how to sort csv with keeping header line

What have you tried? What worked? See How do I post a question effectively?. Questions such as this should be posted as independent questions/new threads since they are not pertinent to the immediate conversation.

If you post your code that reads in your CSV, I can help you sort it. Without that info, your question is ill-defined.

---

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

The safe way would to be using a real CSV parser:

use Text::CSV_XS qw( csv );

my @sorted = sort {
    $a->[5] cmp $b->[5] ||
    $a->[4] cmp $b->[4]
    } @{csv (in => "sorted.csv")};
csv (out => "sorted.csv", in => \@sorted);
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Which could be shortcutted to

csv (in  => [ sort { $a->[5] cmp $b->[5] ||
                     $a->[4] cmp $b->[4]
                     } @{csv (in => "sorted.csv")}],
     out => "sorted.csv");
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1. open your file in read mode, sort the content in memory, close the file, and reopen it in write mode;

2. I usually prefer to keep a copy of the original file, just in case something goes wrong. So I rename the original file (changing the extension to .bak, for example), and then open the renamed original in read mode and write to a new file having the original name (this is basically what the -i command line option does in Perl one-liners). The renamed original file can be deleted at a later point, once it has been verified that everything went right.