Hi! I have very large text files (10GB to 15GB). Each one contains about 40 million lines and 7 fields (see example below).

File looks like this:
99_999_852_F3    chr9    97768833    97768867    ATTTTCTTCAATTACATTTCC
+AATGCTATCCCAAA    +    35
99_999_852_F3    chr9    97885645    97885679    ATTTTCTTCAaTTACATTTCC
+AATGCTATCCCAAA    +    35
99_99_994_F3    chr10    47028821    47028855    AGACAAAAAGGCCATCAACAG
+ATCAGTAAAGGATC    +    35
...
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I need to sort the files based on field-1 (ASCII sorting). I am using Unix  sort -k1 command. Although it works fine, it takes very long time, 30 min to 1 hour. I also tried following Perl script:

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

open (INFILE, "inputfile.txt") or die $!;
open (OUTFILE, '>', "sorted.txt") or die $!;

foreach (sort <INFILE>){
    print OUTFILE $_;
}

close(OUTFILE);
close(INFILE);
exit;
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However, this script puts entire file into memory and sorting process becomes too slow. I was wondering if someone could suggest me a Perl script that will do the sorting faster than Unix  sort -k1 command, and will not use too much memory. Thanks.