If you have the memory something this will probably be faster. You can save on the if/else for every line as well as only doing the minimum in the loop (like not splicing and joining when we don't really need to). Even a saving of a few microseconds X millions of lines is substantial. Multiple calls to print are significantly slower than a single call as the OS can buffer/write more efficiently. 

#!/usr/bin/perl

my ($field,%fh);

while ( <DATA> ) {
    @field = split /,/;
    $fh{$field[2]} .= "$field[0],$field[1],$field[3]";
}

for my $file( keys %fh ) {
    open F, ">$file" or die $!;
    print F $fh{$file};
    close F;
}

[download]

cheers

tachyon

In reply to Re: Performance Trap - Opening/Closing Files Inside a Loop by tachyon
in thread Performance Trap - Opening/Closing Files Inside a Loop by Limbic~Region

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