From Mixing Reads and Writes in perlopentut:
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.
You truncate the file before your read. You probably need to use <+ combined with seek to read the file, go back to the beginning, and then rewrite it (untested). 
#!/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.

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

In reply to Re: sort a csv file then updta the same file by kennethk
in thread sort a csv file then update the same file by john.tm

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