It's a good query.

Currently i can't anser you as i need to take a look into the grep source for that. Currently i'm just greping the file like that :

grep "12345$" myfile

Same for the count :

wc -l myfile

I have another code in Perl for doing what you are suggesting maybe : it first load all the lines in memory, then grep it. But unfortunatly, the result is worst compared to a line by line try (2,47s vs 8,33s). Here is the code used for this test (on a reduced set, 200 mb)

open (FH, '<', "../Tests/10-million-combos.txt");
print "Loading the file...\n";
while (<FH>) {
    push (@_file_to_parse, $_);
}
print "Counting the file...\n";
$NumberOfLine=@_file_to_parse;
print "Searching 123456$...\n";
@_result=grep {/123456$/} @_file_to_parse;
$NumberOfResult=@_result;
print "$NumberOfResult - $NumberOfLine\n";
close FH;

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In reply to Re^4: How to optimize a regex on a large file read line by line ? by John FENDER
in thread How to optimize a regex on a large file read line by line ? by John FENDER

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