geek2007

 Profile Answers by geek2007 

• Jun 21st, 2007

 

you can use the following shell command in your perl script .

 `cat filename|tail -10f ;`

Guest

• Oct 25th, 2007

 

This may not be accepted as well. But this can be done in numerous ways ! One way is here :

maintain a structure which stores the line number and the size of the file at that time.
eg 1 - 10bytes, 2 - 18 bytes ... you'll have to have a counter to increase the number of lines to find out the number of lines in the file. once you are through the file, you'll know the size of the file at any nth line. use sysseek to move the file pointer back to that position ( last 10 )and then start reading till the end.

imavasu

 Profile Answers by imavasu 

• May 13th, 2008

 

Please try this capan module

  use File::Tail;
  $file=File::Tail->new("/some/log/file");
  while (defined($line=$file->read)) {
      print "$line";
  }

  use File::Tail;
  $file=File::Tail->new(name=>$name, maxinterval=>300, adjustafter=>7);
  while (defined($line=$file->read)) {
      print "$line";
  }

rahulashu

 Profile Answers by rahulashu 

• Jun 10th, 2008

 

if we  will passed 2  argument , in that first is  filename  and  second  is no. of  last line then  u can use following  program :

#! /bin/perl

open(MYFILE,$ARGV[0]);

@array = <MYFILE> ;
#print @array ;
$numline = @array;
$numprintline = $numline - $ARGV[1] ;
while($numprintline != $numline)
{
        print "$array[$numprintline]" ;
        $numprintline++;
}

nitashaa

 Profile Answers by nitashaa 

• Jul 16th, 2008

 

#!/usr/bin/perl 
my $count = $ARGV[1];  ---> the number of lines to be printed
while(<>) { ----> reading file passed as arg
my $x = $.;  -----> assigning line number to $x
if ( $count >= $x )
{ print "line number $x: $_n"; }
else { exit; }
}

lbsign

 Profile Answers by lbsign 

• Nov 2nd, 2009

 

I think the point to not using arrays is the fact that loading large files in to an array is expensive.
$times = 10; # this is the number of lines

open(FILE, "$file") or die ("...");
seek(FILE, 0,2);
my $counter =0;
while ($counter < $times && seek(FILE, -2,1)) {
  read(FILE, $chr, 1);
  if ($chr eq "n") { $counter++ }
}

while (<FILE>) {
  print;
}

close(FILE);

diszgaurav

 Profile Answers by diszgaurav 

• Apr 13th, 2010

 

How about opening the file twice and get two filehandles, and then navigate:
#!/usr/bin/env perl
# Usage: $0 <filename> <count>
use warnings;
use strict;

open(FILE1,"$ARGV[0]") or die $!;
open(FILE2,"$ARGV[0]") or die $!;

my $count = $ARGV[1];

while($count--) {
    <FILE1>;
}

while(<FILE1>) {
    <FILE2>;
}

print <FILE2>;

close(FILE1);
close(FILE2);

contactparagm

 Profile Answers by contactparagm 

• Dec 3rd, 2010

 

cat <filename>  | perl -e '$i = 0 ; map { print $_ if ($i++ < 10) } reverse (<>)'

lbsign

 Profile Answers by lbsign 

• Dec 15th, 2010

 

#!/usr/bin/perl

if (@ARGV < 1) {

  die ("Usage: $0 filename [number of lines]n");

}

my $fileName = $ARGV[0];

# defaults to 5 lines if not set

my $noLines = $ARGV[1] || 5;

# Guess how many characters are in a line

my $bytesInLine = 128;

my $bytesInLines = $bytesInLine * $noLines;

open (FILE, "$fileName") or die ("Cannot read $fileNamen");

seek(FILE, 0,2);

my $maxBytes = tell(FILE);

my @fileLines;

my $passCount=0;

my $atBeginFile = 0;

# We want to get the full first line so we get number of lines + 1 

while (@fileLines < $noLines+1) {

  if (!seek(FILE, -1 * $bytesInLines,1)) {

    seek(FILE, 0,0);

    $atBeginFile = 1;

  }

  @fileLines = <FILE>;

  $bytesInLines *= 2;

  $passCount++;

  # you passed the beginning of the file

  if ($atBeginFile) {

    # if the requested lines is above the actual file change it

    $noLines = @fileLines;

    last;

  }

}

my $startIndex = @fileLines - $noLines;

@fileLines = splice(@fileLines, $startIndex,$noLines);

print @fileLines;

print "Tailed $noLines lines in $passCount passesn";

close(FILE);

mohamedmeeran.ss

 Profile Answers by mohamedmeeran.ss 

• Apr 16th, 2011

 

Try this

#!/usr/bin/perl
use strict;
use warnings;

open(FH,"FILENAME") or die "$!";
while ()
{
chomp;
}
print "n$.";
my $x= $. - 10;

close (FH);

open(FH,"FILENAME") or die "$!";
while ()
{
chomp;
if ($.>=$x)
{
  print "$.->$_";
}

}
close (FH);

puneet agrawal

• Mar 29th, 2012

 

I think below answer is suitable.

Code
span style="color: #ff0000;">"imp.txt"$!"


 


 


"

SH

• Mar 29th, 2012

 

Open file, read and print until number of required lines is reached. Memory is saved by not slurping the entire file into an array.

Code
span style="color: #ff0000;">"tailing file $fileName for $lines lines...


""Could not open $fileName"

sergant

 Profile Answers by sergant 

• Apr 27th, 2012

 

Code
#!/usr/bin/perl


"tailing file $fileName for $lines lines...


""Could not open $fileName"

SumitRoy

• Sep 16th, 2012

 

You can also try this :
Create two pointers and make them $count apart.
Move one of the pointer to EOF and keep simultaneously moving the other pointer so that it is $count before.
Now use the second pointer to print the last $count lines.

Code
#!/usr/bin/env perl 


"$ARGV[0]"$!"$ARGV[0]"$!#After this loop FILE1 points to line after $count


#After this loop FILE1 points to EOF and FILE2 points $count before EOF


#Print the last $count lines before EOF

shiva

• Nov 22nd, 2012

 

Just use .. opertor using array just check the length of the array minus with input give by the user
take a difference and do it sample code is below.

Code
 


#! /usr/bin/perl


"Enter the number""


"

Namrata

• Aug 14th, 2013

 

Code
open(FILE, "tail -10f file1.txt |"

pp

• Oct 15th, 2014

 

1) open the file
2) assign it to an array(each line will be an element)
3) Get the length of the array(L)
4) Starting from L-10 .. L , assign elements to another array @new = @old[L-10..L];
5) print the new array , separate elements by newline

vijth

• Oct 19th, 2014

 

Code
open(data, "<file.txt""<data>";}


}

perly

• Mar 6th, 2015

 

Code
#!/usr/bin/perl


 


 


use warnings;


 


use strict;


 


open FILE, "test.txt""Last five lines:


", @last[-5 ... -1];

VINOD

• Apr 1st, 2015

 

You can use File::Readbackwards or File::Tail Cpan modules to read file backwords

• Apr 18th, 2015

 

this may not be accepted as a right answer as we are directly using tail command instead of implementing it logically

RaghsChandu

• May 16th, 2015

 

Code
span style="color: #ff0000;">"@output";

anirudh vikram

• May 30th, 2015

 

Code
 

anirudh

• May 30th, 2015

 

The command-line solution is strict/warnings enabled. The first argument = number of lines to tail
The second argument is the filename of the file for which tailing is required.
Basic algo: keep chopping every line from the end & increment a counter. Stop when either of these 2
conditions are met : i) reached the beginning of file or ii) counter value exceeds the number of lines to be
tailed.
perl -Mstrict -Mwarnings -le
($a, $_) = (shift||5, join"",<>); my($k, @A);
unshift @A, $1 while s/(.*)
$// && $k++ < $a;
print for @A;
num_of_lines_to_be_tailed file_to_be_tailed

anirudh

• May 31st, 2015

 

Always keep the number of lines in array @A equal to $b.
Whenver, it crosses the threshold of ($b) clip from the top of array.
And at the end, print the array.
perl -lne BEGIN{ $b = shift; }
push @A, $_;
shift @A if @A > $b;
END { print for @A; } num_of_lines_to_tail yourfile

saminathan

• Jun 4th, 2015

 

use the command "tail -10

Arunesh

• Jun 15th, 2015

 

You can do it in one liner

Code
span style="color: #0000ff;">$_$_

soumdgr8

• Aug 1st, 2015

 

If its UNIX (ish) Env., use below

Code
#tail.pl


#this will work for default behaviour of tail(i.e. last 10 lines), you can enhance it to tail certain no. of lines


#usage : tail.pl <filename>


#!/usr/bin/perl -w


#take line count of file


`wc -l $ARGV[0] | cut -d" " -f1`);


#caculate which line to start printing from


#if file is less than 10 lines, print everything else print last 10 lines


$.