How to read last 50 lines of a log file

I guess this is general Perl question. I want to display the last 50 lines of log
file. I found few examples, showing read entire file to an array and take the
last 50 lines. But if log file is too big, I guess this may not be a good choice.
Anybody has suggestions? Thanks Sri

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kaalraa

I guess this is general Perl question. I want to display the last 50 lines of log
file. I found few examples, showing read entire file to an array and take the
last 50 lines. But if log file is too big, I guess this may not be a good choice.
Anybody has suggestions? Thanks Sri

Want to display the last 50 lines ... but where? On screen or in a file? Please be more elaborate about the requirement.

Still, to display on screen...the command "tail -50f {filename}" can be used.

Srinivasa Talla

Sorry, to display on web page(Win 2003, IE 6). Thanks.

Adam Stoller

Want to display the last 50 lines ... but where? On screen or in a file? Please be more elaborate about the requirement.

Still, to display on screen...the command "tail -50f {filename}" can be used.

tail is a Unix tool. There are Windows versions that can be found (and if you're stuck on Windows it's probably not a bad idea), but some of them may not be desirable to download and install on something like a production TS server.

There's a CPAN module called File::Tail - which I haven't used but looks like it might be a reasonable way to implement a tail program in a platform-independent way (it has some nice features that regular tail doesn't include - like being able to re-open a file that's being tail'ed after the file has been truncated or removed and re-created).

However - for simple purposes you could using something like:

#!/path/to/perl
use strict;
use warnings;
my $max_lines = shift;
my @buffer;
while(<STDIN>){
    push(@buffer, $_);
    shift(@buffer) if (@buffer > $max_lines);
}
print foreach(@buffer);

This is assuming using like: tail.ipl 10 < filename

Feel free to revise / rewrite as you need / desire - I just threw the above together quickly right now.

Srinivasa Talla

Thanks fish, nice input to me. It is very help full. Like C(seek, I guess), we can't able to go directly to the end of file and come back.

Adam Stoller

Thanks fish, nice input to me. It is very help full. Like C(seek, I guess), we can't able to go directly to the end of file and come back.

You might be able to use Perl's seek, read, sysseek and/or sysread to do this too - but as I've never had much (apparent) need to use those functions, I haven't tried, but looking at the perldoc for them, they tend to operate in terms of bytes rather than lines, which would probably make it less trivial.

edillon

Here is a script you might find handy which runs on Windows and will list the (entire) contents of the error log and freshest debug file. It wilol go to the last line entered in whatever file you are listing. Modify the paths to your own files...hope it helps.

#!D:\Apps\Interwoven\TeamSite\iw-perl\bin\iwperl
#################################################
# Author: Eric Dillon
#################################################
use strict;
use Tk;
use Tk::NoteBook;

my $mw = MainWindow->new();
$mw->geometry( "700x550" );
my $book = $mw->NoteBook()->pack( -fill=>'both', -expand=>1 );

# Set up tabs. They will appear in the order they are listed here
my $tab1 = $book->add( "Sheet 1", -label=>"Perl Error Log", -createcmd=>\&getErrorLog );
my $tab2 = $book->add( "Sheet 2", -label=>"TeamSite Debug", -raisecmd=>\&getTsLog );

# Build refresh button
$mw->Button(-text => ' EXIT Program ', -command => sub { exit },)->pack(-side => 'left');
my $but = $mw->Button(-text=>" Refresh Log Window ", -command =>\&getErrorLog) -> pack(-side => 'right');

MainLoop;

########################
# Show Error Log
########################
sub getErrorLog {
my $filename = "D:\\Apps\\Interwoven\\TeamSite\\local\\logs\\iwui\\error.log";
$but->configure(-command =>\&getErrorLog);
my $txt = $tab1->Text(-width => 95, -height => 30, -wrap => 'none');
$txt->pack(-expand => 1);
my $srl_y = $tab1 -> Scrollbar(-orient=>'v',-command=>[yview => $txt]);
my $srl_x = $tab1 -> Scrollbar(-orient=>'h',-command=>[xview => $txt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y],
-xscrollcommand=>['set',$srl_x]);
$txt -> grid(-row=>1,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$tab1 -> grid(-row=>5,-column=>1,-columnspan=>2);
my $line_cnt=0;
open (LOG, "<$filename") || die"Could not open file $filename to read: $!";
while () {
$line_cnt++;
$txt->insert('end', $line_cnt.". ".$_);
}
close LOG;
$txt->yview(-pickplace=>$line_cnt);
return;
}

########################
# Show newest TeamSite debug file
########################
sub getTsLog {
my $debug_dir = "D:\\Apps\\Interwoven\\TeamSite\\tmp";
opendir ( DIR, "$debug_dir" ) || warn ( "Can't read $debug_dir directory.!\n" );
my @entries = sort { -M $a <=> -M $b } # newest files first
grep { m/.txt|.log|.xml/i } # only grab files--skip dirs
readdir DIR;

my $entry = shift @entries;
my $filename = "$debug_dir\\" . $entry;
$but->configure(-command =>\&getTsLog);
my $txt = $tab2->Text(-width => 95, -height => 30, -wrap => 'none');
$txt->pack(-expand => 1);
my $srl_y = $tab2 -> Scrollbar(-orient=>'v',-command=>[yview => $txt]);
my $srl_x = $tab2 -> Scrollbar(-orient=>'h',-command=>[xview => $txt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y],
-xscrollcommand=>['set',$srl_x]);
$txt -> grid(-row=>1,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$tab2 -> grid(-row=>5,-column=>1,-columnspan=>2);
my $line_cnt=0;
open (LOG, "<$filename") || die"Could not open file $filename to read: $!";
while () {
$line_cnt++;
$txt->insert('end', $line_cnt.". ".$_);
}
close LOG;
$txt->yview(-pickplace=>$line_cnt);
return;
}

#################################################

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