How do I implement 'tail -f' with timeout-on-read in Perl?

perl progress.tracker.pl progress.tracker.pl

#!/usr/perl/v5.10.0/bin/perl -w
#
# @(#)$Id: progress.tracker.pl,v 1.3 2009/01/09 17:32:45 jleffler Exp jleffler $
#
# Track progress of a log-generating process by printing one dot per line read.

use strict;
use constant DOTS_PER_LINE => 50;
use constant LINES_PER_BREAK => 25;
use constant debug => 0;
use POSIX qw( strftime );
use Sys::AlarmCall;

sub read_line
{
    print "-->> read_line()n" if debug;
    my $line = <STDIN>;
    printf "<<-- read_line(): %s", (defined $line) ? $line : "n" if debug;
    return $line;
}

my $line_no = 0;
my $timeout = 30;
my $line;

$| = 1;     # Unbuffered output

while ($line = alarm_call($timeout, 'read_line', undef))
{
    $line_no++;
    print ".";
    print "n" if ($line_no % DOTS_PER_LINE == 0);
    printf "%sn", strftime("%Y-%m-%d %H:%M:%S", localtime(time))
        if ($line_no % (DOTS_PER_LINE * LINES_PER_BREAK) == 0);
    last if $line =~ m/^Trace run finished: /;
}

print "n";
print $line if defined $line && $line =~ m/^Trace run finished: /;

#!/usr/perl/v5.10.0/bin/perl -w
#
# @(#)$Id: progress.tracker.pl,v 3.2 2009/01/14 07:17:04 jleffler Exp $
#
# Track progress of a log-generating process by printing one dot per line read.

use strict;
use POSIX qw( strftime );
use File::Tail;

use constant DOTS_PER_LINE   => 50;
use constant LINES_PER_BREAK => 25;
use constant MAX_TIMEOUTS    => 10;
use constant TIMEOUT_LENGTH  => 30; # Seconds

my $timeout    = TIMEOUT_LENGTH;
my $line_no    = 0;
my $n_timeouts = 0;
my $line;

sub print_item
{
    my($item) = @_;
    $line_no++;
    print "$item";
    print "n" if ($line_no % DOTS_PER_LINE == 0);
    printf "%sn", strftime("%Y-%m-%d %H:%M:%S", localtime(time))
        if ($line_no % (DOTS_PER_LINE * LINES_PER_BREAK) == 0);
}

$| = 1;     # Unbuffered output

# The foreach and while loops are cribbed from File::Tail POD.
my @files;
foreach my $file (@ARGV)
{
    push(@files, File::Tail->new(name=>"$file", tail => -1, interval => 2));
}

while (1)
{
    my ($nfound, $timeleft, @pending) = File::Tail::select(undef, undef, undef, $ti


        perl timeout




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edited Jan 18 '09 at 17:45

    asked Jan 14 '09 at 0:19Jonathan Leffler112k787208

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    Have you tried File::Tail to handle the actual tailing instead of trying to coerce <STDIN> to do the job?

Or, if that piece does work, in what way is this failing?




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    answered Jan 14 '09 at 0:23Dave Sherohman15.1k21850















        No; I&#39;ve not yet tried it.  But I will...  I should have known, I suppose.  My search on timeout didn&#39;t find that. &ndash;&nbsp;Jonathan Leffler Jan 14 '09 at 0:24




        How do you do it for a non-file device, like &#47;dev&#47;ttyUSB0

grep -m 1 pattern <(tail -n 0 -f file)

ssh login@hostname 'grep -m 1 pattern <(tail -n 0 -f file)'

ssh login@hostname 'grep -m 1 pattern <(unbuffer -p tail -n 0 -f file)'