http://qs321.pair.com?node_id=998528

hmb104 has asked for the wisdom of the Perl Monks concerning the following question:

Good afternoon dear Monks,

I'm attempting to search logs using tail -f so if the specific string got into the log file we should print the first 3 occurrences and continue the rest of the script, but it is not working. The strings passed as a commandline argument.

I appreciate the your valuable input

use warnings;
use strict;

my $currentDate = `date +%Y%m%d`;
my $logPath = "/dhcp/logs"
my $logFile = "{$path}/DHCPD.log.{$currentDate}"
my @tail = qx(tail -f -1 $logFile | grep $_);

if (@tail) {
  print @slice = @tail[0 - 2];
  last;
} 
else {
  print "not found";
}

[download]

Replies are listed 'Best First'.
Re: Watch log for string (tail -f)
by BrowserUk (Patriarch) on Oct 11, 2012 at 20:19 UTC
    but it is not working

    Is it sleeping on the job, or just not getting out of bed? :)

    Does it hang; print 'not found'; explode in a rain of pink fairies?

    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.

    RIP Neil Armstrong
[reply]

      lol, yes it keep going and going and going. Any ideas about how to make it exit once 3 occurrences are cough in the tail -f command?

[reply]

        tail -f doesn't end until you interrupt it. Try something like this: 

        #! perl -slw
use strict;

my $pid = open TAIL, '-|', 'tail -f theLog' or die $!;
my @matches;
while( @matched <3 and defined( $_ = <TAIL> ) ) {
      push @matches, $_ if /the search term/;
}

kill 2, $pid;

## do something with the 3 lines in @matches.

        [download]
        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.

        RIP Neil Armstrong
[reply]
[d/l]
[select]
Re: Watch log for string (tail -f)
by roboticus (Chancellor) on Oct 11, 2012 at 20:25 UTC

    hmb104:

    "Not working" isn't particularly helpful. What is it doing? Any error messages, etc.?

    Anyway, here's how I process the a log file with tail -f:

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

open my $FH, 'tail -f t |' or die;

while (<$FH>) {
    chomp;
    # processing goes here....
}

    [download]

    ...roboticus

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

[reply]
[d/l]
[select]
Re: Watch log for string (tail -f)
by brap (Pilgrim) on Oct 11, 2012 at 20:24 UTC
[reply]
[d/l]
Re: Watch log for string (tail -f)
by live4tech (Sexton) on Oct 12, 2012 at 11:01 UTC

    I think the tail -f will continue until interrupted as other posters pointed out.

    I was wondering also why you used {$path} in the line my $logFile = "{$path}/DHCPD.log.{$currentDate}" rather than the variable you created, {$logPath}?

    Is this a typo?

[reply]
[d/l]
[select]

      That was a typo and I have fxed it. I'm still not getting any idea abou7t how to do this, and how to break out the tail -f?

      This is what I got so far:

      #!/NMS/perl/ACTIVE/bin/perl -w

use warnings;
use strict;

#variables
my $currentDate = `date +%Y%m%d`;
my $logPath = "/logs";
my $logFile = "$logPath/log.$currentDate";
my $ipaddress = $ARGV[0];
my @tail = `tail -f $logFile | grep $ipaddress`;

#print "Log file: $logFile\n";
#print "IP address: $ipaddress\n";

# script begins
if (@tail) {
 my @lines = $tail[0 - 2];
 print @lines;
 exit(0);
} 
else {
  print "not found";
  exit(1);
}

      [download]
[reply]
[d/l]

        I think you will need to use the file handle with the while loop as the other posters have suggested. Have you tried this?

[reply]

Back to Seekers of Perl Wisdom