Re^2: How does the while works in case of Filehandle when reading a gigantic file in Perl

You are opening and closing your output file for every line you read.

Opening a file is timewise an "expensive" operation. As the file is opened for appending new lines to it, opening the file will take longer and longer, since the OS has to find the end of file to add the new line to it.

Solution: open the output file in the beginning of your script and close it at the end. You should see an immediate speed improvement.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

My blog: Imperial Deltronics

Comment on Re^2: How does the while works in case of Filehandle when reading a gigantic file in Perl

Replies are listed 'Best First'.
Re^3: How does the while works in case of Filehandle when reading a gigantic file in Perl by raj4489 (Acolyte) on Feb 06, 2015 at 12:36 UTC
I have checked the timings for all the steps individually, and no step in the while loop takes anymore time (it remains constant). But only when getting in the while, the time keeps on increasing for every new line.	[reply]
Re^4: How does the while works in case of Filehandle when reading a gigantic file in Perl by CountZero (Bishop) on Feb 06, 2015 at 19:45 UTC
Did you try the solution I suggested? CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James My blog: Imperial Deltronics	[reply]