Hello, suppose I have a huge file "test_file.csv" (about 40GB). And I want to add a line at the beginning of the file without reading the whole file and rewriting it (since it takes a LOT of time). I tried "sed -i ..." and "perl -pi" but they are very slow. Finally I came around something like this: 
$output_filename="text_file.csv";
open (FH, "+< $output_filename") or die "can't open";
my $line =<FH>;
seek FH, 0,0;
print FH "This is my header \n".$line;

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But instead of prepending the line, it is replacing the existing lines!! i.e.
----------test_file.csv---------------
line 1
line 2
line 3
---------------------------------------

=> run the perl code

-------test_file.csv------------------
This is my header
ine 3
------------------------------------------


Any ideas?
Thanks!

In reply to Prepending header line to HUGE csv file by Anonymous Monk

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