Re: print a file from Bottom to Top (reverse order)

I want to go with while loop.

Why? Given what you're doing in your second code sample, you could do it as well on the items of the @file array in your first code sample.

For example:

open(FILE, "<myfile.txt");
@file = reverse <FILE>;
foreach (@file) {
   chomp;                              # --> Note: no need to chomp, i
+t just forces you to add the \n again when you print
   next unless /\S/; # skip blank lines  --> Note: this is useless giv
+en that you print only line matching the /Passed CLEAN/ pattern
   if (/Passed CLEAN/) { #search string Passed CLEAN
      print "$_ \n"; # print ALL lines containing Passed CLEAN

   }
}
[download]

Or, simplifying a bit the syntax:

open(FILE, "<myfile.txt");
@file = reverse <FILE>;
foreach (@file) {
   print if /Passed CLEAN/;
}
[download]

That should work fine unless your file is truly huge and won't fit into memory. If your file is too big, then the File::ReadBackwards is the only simple solution;

Comment on Re: print a file from Bottom to Top (reverse order) Select or Download Code

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Re^2: print a file from Bottom to Top (reverse order) by theravadamonk (Scribe) on Jun 20, 2018 at 18:29 UTC
Thank you very much for your code. it works as expected. my file is actually maillog file. It's sometimes huge. So File::ReadBackwards is much better. But, the problem is I am trying to insert below lines in to that code. `if (/Passed CLEAN/) { #search string Passed CLEAN print "$_ \n"; # print ALL lines containing Passed CLEAN }` [download] But, still no success. I am learning perl. I am still a novice. I googled how to insert it, But, still not lucky.	[reply] [d/l]
Re^3: print a file from Bottom to Top (reverse order) by Laurent_R (Canon) on Jun 20, 2018 at 18:45 UTC
Changing just a couple of small things to haukex's solution above should give you what you need: `use warnings; use strict; use File::ReadBackwards; my $bw = File::ReadBackwards->new('/var/log/maillog') or die $!; while (defined( my $line = $bw->readline )) { print $line if $line =~ /Passed CLEAN/; } $bw->close;` [download]	[reply] [d/l]
Re^4: print a file from Bottom to Top (reverse order) by theravadamonk (Scribe) on Jun 22, 2018 at 15:45 UTC
Thanks a lot for your kind reply. I get what I expect from your INPUT. I thank all who participated in this mail tread.	[reply]
Re^3: print a file from Bottom to Top (reverse order) by AnomalousMonk (Archbishop) on Jun 20, 2018 at 19:04 UTC
Given Laurent_R's comprehensive reply, let's move on to the next question: How do I match one or more arbitrary whitespace characters between the `'Passed'` and the `'CLEAN'` in the pattern match? Please see the `+` quantifier in perlre, and `\s` in perlre and Whitespace in perlrecharclass. In general, please see perlretut. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]