ChRy0 has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks!, i want to tail -f a access log and only print 'new' entries, not the entire logfile. I currently have this code, but that also prints the old contents which i don't want.. 


#!/usr/bin/perl

use strict;
use warnings;

my $logfile = "/var/log/httpd/agent1_access.log";

open(FH,'<',$logfile) || handle_error();  # typical open call
for (;;) {
    while (<FH>) {
      print "$_";
    }
    # eof reached on FH, but wait a second and maybe there will be mor
+e output
    sleep 1;
    seek FH, 0, 1;      # this clears the eof flag on FH
}

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Replies are listed 'Best First'.
Re: tailing a file without printing its entire contents
by BrowserUk (Patriarch) on Aug 07, 2014 at 12:00 UTC

    If you place the seek, with to-end, above the while loop, it'll skip over the existing content the first time you read the file: 

    use strict;
use warnings;

my $logfile = "/var/log/httpd/agent1_access.log";

open(FH,'<',$logfile) || handle_error();  # typical open call
for (;;) {
    seek FH, 0, 2;      # this clears the eof flag on FH
    # eof reached on FH, but wait a second and maybe there will be mor
+e output
    sleep 1;
    while (<FH>) {
      print "$_";
    }
}

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    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
      Thanks, exactly what i was looking for!
[reply]
Re: tailing a file without printing its entire contents
by roboticus (Chancellor) on Aug 07, 2014 at 12:04 UTC

    ChRy0:

    Another module that may be useful: File::Tail.

    ...roboticus

    When your only tool is a hammer, all problems look like your thumb.

[reply]
Re: tailing a file without printing its entire contents
by Athanasius (Archbishop) on Aug 07, 2014 at 11:58 UTC
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Re: tailing a file without printing its entire contents
by bulrush (Scribe) on Aug 09, 2014 at 13:02 UTC
    Another possibility, untested. 
    open(FH, 'logfile.txt') || die "Could not op en logfile.txt";
@arr=<FH>; # Read whole file into array. 
my $lines=10; # Print last 10 lines
my $start=$#arr-$lines;
for $i (@arr($start..$#arr))
    {
    print "$arr[$i]\n";
    }
close(FH);

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    Perl 5.8.8 on Redhat Linux RHEL 5.5.56 (64-bit)
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[d/l]

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