Read File Backword

gjeffrey has asked for the wisdom of the Perl Monks concerning the following question:

Revered Monks:

One of my co-workers just asked me a very interesting question: Is there a way to process a file from the bottom up instead of from the top? In other words, is there something I can do so that the loop

  while (<FILE>)
  {
    ## some processing
   }
[download]

will process the file beginning with the last line of the file?

Comment on Read File Backword Download Code

Replies are listed 'Best First'.
Re: Read File Backword by sweetblood (Prior) on Jul 27, 2004 at 19:40 UTC
check out File::ReadBackwards HTH Sweetblood	[reply]
Re^2: Read File Backword by eserte (Deacon) on Jul 27, 2004 at 19:45 UTC
... which is more efficient on large files than Tie::File.	[reply]
Re^3: Read File Backword by coec (Chaplain) on Jul 28, 2004 at 01:46 UTC
Given that Tie::File reads the whole file into an array whereas File::ReadBackwards just 'reads the file backwards', definately File::ReadBackwards is more efficient. I converted a KSH script to Perl, using File::ReadBackwards and got a 400x increase in speed. YMMV CC I should have mentioned that the KSH script was not badly written. It also parsed many files that were 300-500M in size, where the info it needed was typically in the last thousand lines.	[reply]
Re: Read File Backword by blue_cowdawg (Monsignor) on Jul 27, 2004 at 19:33 UTC
s there a way to process a file from the bottom up instead of from the top? `use Tie::File; my @ray=(); tie @ray,"Tie::File","myfile" or die $!; for(my $i=$#ray;$i>=0; $i--){ my $line=$ray[$i]; # do something with it... } untie @ray;` [download] Caveat:thoroughly untest!	[reply] [d/l]
Re^2: Read File Backword by gjeffrey (Acolyte) on Jul 27, 2004 at 19:44 UTC
Thanks for the super quick response. Does this mean that all the file is read into memory before we can access `$ray[$#ray]` [download] If this is the case for extremely large files 1GB, I may have a problem.	[reply] [d/l]
Re^3: Read File Backword by pg (Canon) on Jul 27, 2004 at 19:50 UTC
No. I read the source code before. It only reads in lines when it is needed, besides it deletes lines from memory when the buffer overflows. Memory is not a concern for that module.	[reply]