LogPauseDetector.pl

#!/usr/bin/perl

# The following POD section contains placeholders, so it has to be preprocessed by this script first.
#
# HelpBeginMarker

=head1 OVERVIEW

SCRIPT_NAME version SCRIPT_VERSION

This tool forwards lines of text unchanged, as long as they flow without interruption.
When a pause is detected, the pause duration is inserted surrounded by empty lines.

=head1 RATIONALE

When inspecting logs in real time with a command like I<< tail -F /var/log/syslog >>S< >,
I have developed a habit of pressing the Enter key in order to separate the old text lines
from the new ones the next event will generate.

In the meantime, I got tired of manually hitting the Enter key, so I wrote this script
to automate such a visual separation of log line groups.

Log line separation is based on simple timing (a configurable pause), so it
will probably not be ideal. Maybe a future version of this script will include
some user-defined regular expressions in order to separate
log line groups more intelligently.

When used with syslog, the output looks like this:

  Oct 29 21:30:06 myhostname myusername: Log line 1
  Oct 29 21:30:06 myhostname myusername: Log line 2

  < pause of 5.812 seconds >

  Oct 29 21:30:12 myhostname myusername: Log line 3
  Oct 29 21:30:12 myhostname myusername: Log line 4

=head1 USAGE

S<perl SCRIPT_NAME [options] [--] E<lt>filenameE<gt>>

If the filename is a single hyphen ('-'), or is omitted, then data is read from stdin.
This is useful when piping between processes.

If you always want the English thousands separator (',') and decimal separator ('.')
in the pause duration values, no matter what the current locale is,
set environment variable LANG=C before running this script. The easiest way is like this:

  env LANG=C  perl SCRIPT_NAME ...

When piping stdout from other processes to this script, stdout buffering may cause
the data stream to 'stutter'. See tools I<< unbuffer >> and I<< S<< stdbuf -o0 >> >> for more information.

Usage example:

 tail -F /var/log/syslog | perl SCRIPT_NAME

=head1 OPTIONS

=over

=item *

B<--no-hints>

Do not print any hints, just the received log lines (and the pause indications).

=item *

B<< --pause-detection=n >>

If a pause of at least the given number of seconds is detected,
insert the pause duration surrounded by empty lines.

These indications make it easier to spot pauses in the received data,
and it can help visually delimit event boundaries, assuming that there are
meaningful pauses between unrelated log lines.

The default is DEFAULT_PAUSE_SEC seconds (DEFAULT_PAUSE_MS ms).

A number of 0 seconds disables these pause indications, but that does not make sense
at the moment, because this is the only functionality that this tool currently provides.

=item *

B<--show-microseconds>

Display timing information down to microseconds.

If you need this level of accuracy, make sure that your system can actually deliver it.
Start by finding out the timing resolution:

  perl -MTime::HiRes -e 'print Time::HiRes::clock_getres( CLOCK_REALTIME ) . "\n"'

=item *

B<-h, --help>

Print this help text.

=item *

B<--help-pod>

Preprocess and print the POD section. Useful to generate the README.pod file.

=item *

B<--version>

Print this tool's name and version number (SCRIPT_VERSION).

=item *

B<--license>

Print the license.

=item *

B<-->

Terminate options processing. Useful to avoid confusion between options and filenames
that begin with a hyphen ('-'). Recommended when calling this script from another script,
where the filename comes from a variable or from user input.

=back

=head1 EXIT CODE

Exit code: 0 on success, some other value on error.

=head1 SIGNALS

SIGINT (Ctrl+C) and SIGHUP (closing the terminal window) cause the script to print a message
about having received the signal, assuming that hints have not been disabled. The script then
kills itself with the same signal.

=head1 CAVEATS

=over

=item * The pause detection indication may break a text line into 2 parts.

You would not normally expect a pause to fall in the middle of a text line, but it might happen.
When it does, it looks like this:

  This line is brPAUSE_INSIDE_LINE_HINT_END

  < pause of 0,226 seconds >

  PAUSE_INSIDE_LINE_HINT_BEGINoken into 2 parts.

The output of this script is designed mainly for human consumption. If you try to analyse
the resulting output with an log parsing tool, removing the pause indications may not be enough,
and log parsing may break. Therefore, it is best to store an unmodified copy of the log lines
for parsing purposes, using perhaps a tool like 'tee'.

=item * There are performance limitations.

The Perl interpreter is not very fast, so do not expect a high throughput or timing accuracy.

There is a considerable start-up delay due to Perl interpreter initialisation.
If you are starting the script and immediately feeding it with data,
the timing for the first log lines will probably be inaccurate due
to this delay.

This script will probably only keep up with moderate data rates.

=item *

This script is sensitive to changes to the clock.

If the local time changes, the pause durations reflected in the log will not be accurate.

=item * A Perl interpreter with 64-bit integer support is required.

That should actually be the case for all modern Perl distributions, even on 32-bit operating systems.
This script does check, but you can also manually find out like this:

  perl -V | grep USE_64_BIT_INT

Otherwise, you would quickly encounter integer overflows. Using multiprecision arithmetic would be too slow.

=back

=head1 FEEDBACK

Please send feedback to rdiezmail-tools at yahoo.de

=head1 LICENSE

Copyright (C) 2023 R. Diez

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License version 3 as published by
the Free Software Foundation.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License version 3 for more details.

You should have received a copy of the GNU Affero General Public License version 3
along with this program.  If not, see L<http://www.gnu.org/licenses/>.

=cut

# HelpEndMarker

use strict;
use warnings;

use FindBin qw( $Bin $Script );
use Config;
use Getopt::Long;
use Pod::Usage;
use Time::HiRes qw();
use POSIX;

use constant SCRIPT_VERSION => "1.01";

use constant EXIT_CODE_SUCCESS => 0;
use constant EXIT_CODE_FAILURE => 1;  # Beware that other errors, like those from die(), can yield other exit codes.

use constant TRUE  => 1;
use constant FALSE => 0;

use constant PAUSE_INSIDE_LINE_HINT_END   => " [this line continues further below]";
use constant PAUSE_INSIDE_LINE_HINT_BEGIN => "[this line started further above] ";

use constant DEFAULT_PAUSE_MS  => 200;
use constant DEFAULT_PAUSE_SEC => "0.2";


# ----------- Generic constants and routines -----------

sub write_stdout ( $ )
{
  ( print STDOUT $_[0] ) or
     die "Error writing to standard output: $!\n";
}

sub write_stderr ( $ )
{
  ( print STDERR $_[0] ) or
     die "Error writing to standard error: $!\n";
}


sub flush_stdout ()
{
  if ( ! defined( STDOUT->flush() ) )
  {
    # The documentation does not say whether $! is set. I am hoping that it does,
    # because otherwise there is no telling what went wrong.
    die "Error flushing standard output: $!\n";
  }
}


#------------------------------------------------------------------------
#
# Reads a whole binary file, returns it as a scalar.
#
# Security warning: The error messages contain the file path.
#
# Alternative: use Perl module File::Slurp
#

sub read_whole_binary_file ( $ )
{
  my $file_path = shift;

  open( my $file, "<", $file_path )
    or die "Cannot open file \"$file_path\": $!\n";

  binmode( $file )  # Avoids CRLF conversion.
    or die "Cannot access file in binary mode: $!\n";

  my $file_content;
  my $file_size = -s $file;

  my $read_res = read( $file, $file_content, $file_size );

  if ( not defined($read_res) )
  {
    die qq<Error reading from file "$file_path": $!>;
  }

  if ( $read_res != $file_size )
  {
    die qq<Error reading from file "$file_path".>;
  }

  close( $file ) or die "Cannot close file descriptor: $!\n";

  return $file_content;
}


sub get_pod_from_this_script ()
{
  # POSSIBLE OPTIMISATION:
  #   We do not actually need to read the whole file. We could read line-by-line,
  #   discard everything before HelpBeginMarker and stop as soon as HelpEndMarker is found.

  my $sourceCodeOfThisScriptAsString = read_whole_binary_file( "$Bin/$Script" );

  # We do not actually need to isolate the POD section, but it is cleaner this way.

  my $regex = "# HelpBeginMarker[\\s]+(.*?)[\\s]+# HelpEndMarker";

  my @podParts = $sourceCodeOfThisScriptAsString =~ m/$regex/s;

  if ( scalar( @podParts ) != 1 )
  {
    die "Internal error isolating the POD documentation.\n";
  }

  my $podAsStr = $podParts[0];


  # Replace some known placeholders. This is the only practical way to make sure
  # that the script name and version number in the help text are always right.
  # If you duplicate name and version in the source code and in the help text,
  # they will inevitably get out of sync at some point in time.
  #
  # There are faster ways to replace multiple placeholders, but optimising this
  # is not worth the effort.

  $podAsStr =~ s/SCRIPT_VERSION/@{[ SCRIPT_VERSION ]}/gs;
  $podAsStr =~ s/SCRIPT_NAME/$Script/gs;

  $podAsStr =~ s/PAUSE_INSIDE_LINE_HINT_END/@{[ PAUSE_INSIDE_LINE_HINT_END ]}/gs;
  $podAsStr =~ s/PAUSE_INSIDE_LINE_HINT_BEGIN/@{[ PAUSE_INSIDE_LINE_HINT_BEGIN ]}/gs;

  $podAsStr =~ s/DEFAULT_PAUSE_MS/@{[ DEFAULT_PAUSE_MS ]}/gs;
  $podAsStr =~ s/DEFAULT_PAUSE_SEC/@{[ DEFAULT_PAUSE_SEC ]}/gs;

  return $podAsStr;
}


sub print_help_text ()
{
  my $podAsStr = get_pod_from_this_script();


  # Prepare an in-memory file with the POD contents.

  my $memFileWithPodContents;

  open( my $memFileWithPod, '+>', \$memFileWithPodContents )
    or die "Cannot create in-memory file: $!\n";

  binmode( $memFileWithPod )  # Avoids CRLF conversion.
    or die "Cannot access in-memory file in binary mode: $!\n";

  ( print $memFileWithPod $podAsStr ) or
    die "Error writing to in-memory file: $!\n";

  seek $memFileWithPod, 0, 0
    or die "Cannot seek inside in-memory file: $!\n";


  write_stdout( "\n" );

  # Unfortunately, pod2usage does not return any error indication.
  # However, if the POD text has syntax errors, the user will see
  # error messages in a "POD ERRORS" section at the end of the output.

  pod2usage( -exitval    => "NOEXIT",
             -verbose    => 2,
             -noperldoc  => 1,  # Perl does not come with the perl-doc package as standard (at least on Debian 4.0).
             -input      => $memFileWithPod,
             -output     => \*STDOUT );

  $memFileWithPod->close()
    or die "Cannot close in-memory file: $!\n";
}


sub get_license_text ()
{
  return ( <<EOL

                    GNU AFFERO GENERAL PUBLIC LICENSE
                       Version 3, 19 November 2007

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license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly and
finally terminates your license, and (b) permanently, if the copyright
holder fails to notify you of the violation by some reasonable means
prior to 60 days after the cessation.

  Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.

  Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License.  If your rights have been terminated and not permanently
reinstated, you do not qualify to receive new licenses for the same
material under section 10.

  9. Acceptance Not Required for Having Copies.

  You are not required to accept this License in order to receive or
run a copy of the Program.  Ancillary propagation of a covered work
occurring solely as a consequence of using peer-to-peer transmission
to receive a copy likewise does not require acceptance.  However,
nothing other than this License grants you permission to propagate or
modify any covered work.  These actions infringe copyright if you do
not accept this License.  Therefore, by modifying or propagating a
covered work, you indicate your acceptance of this License to do so.

  10. Automatic Licensing of Downstream Recipients.

  Each time you convey a covered work, the recipient automatically
receives a license from the original licensors, to run, modify and
propagate that work, subject to this License.  You are not responsible
for enforcing compliance by third parties with this License.

  An "entity transaction" is a transaction transferring control of an
organization, or substantially all assets of one, or subdividing an
organization, or merging organizations.  If propagation of a covered
work results from an entity transaction, each party to that
transaction who receives a copy of the work also receives whatever
licenses to the work the party's predecessor in interest had or could
give under the previous paragraph, plus a right to possession of the
Corresponding Source of the work from the predecessor in interest, if
the predecessor has it or can get it with reasonable efforts.

  You may not impose any further restrictions on the exercise of the
rights granted or affirmed under this License.  For example, you may
not impose a license fee, royalty, or other charge for exercise of
rights granted under this License, and you may not initiate litigation
(including a cross-claim or counterclaim in a lawsuit) alleging that
any patent claim is infringed by making, using, selling, offering for
sale, or importing the Program or any portion of it.

  11. Patents.

  A "contributor" is a copyright holder who authorizes use under this
License of the Program or a work on which the Program is based.  The
work thus licensed is called the contributor's "contributor version".

  A contributor's "essential patent claims" are all patent claims
owned or controlled by the contributor, whether already acquired or
hereafter acquired, that would be infringed by some manner, permitted
by this License, of making, using, or selling its contributor version,
but do not include claims that would be infringed only as a
consequence of further modification of the contributor version.  For
purposes of this definition, "control" includes the right to grant
patent sublicenses in a manner consistent with the requirements of
this License.

  Each contributor grants you a non-exclusive, worldwide, royalty-free
patent license under the contributor's essential patent claims, to
make, use, sell, offer for sale, import and otherwise run, modify and
propagate the contents of its contributor version.

  In the following three paragraphs, a "patent license" is any express
agreement or commitment, however denominated, not to enforce a patent
(such as an express permission to practice a patent or covenant not to
sue for patent infringement).  To "grant" such a patent license to a
party means to make such an agreement or commitment not to enforce a
patent against the party.

  If you convey a covered work, knowingly relying on a patent license,
and the Corresponding Source of the work is not available for anyone
to copy, free of charge and under the terms of this License, through a
publicly available network server or other readily accessible means,
then you must either (1) cause the Corresponding Source to be so
available, or (2) arrange to deprive yourself of the benefit of the
patent license for this particular work, or (3) arrange, in a manner
consistent with the requirements of this License, to extend the patent
license to downstream recipients.  "Knowingly relying" means you have
actual knowledge that, but for the patent license, your conveying the
covered work in a country, or your recipient's use of the covered work
in a country, would infringe one or more identifiable patents in that
country that you have reason to believe are valid.

  If, pursuant to or in connection with a single transaction or
arrangement, you convey, or propagate by procuring conveyance of, a
covered work, and grant a patent license to some of the parties
receiving the covered work authorizing them to use, propagate, modify
or convey a specific copy of the covered work, then the patent license
you grant is automatically extended to all recipients of the covered
work and works based on it.

  A patent license is "discriminatory" if it does not include within
the scope of its coverage, prohibits the exercise of, or is
conditioned on the non-exercise of one or more of the rights that are
specifically granted under this License.  You may not convey a covered
work if you are a party to an arrangement with a third party that is
in the business of distributing software, under which you make payment
to the third party based on the extent of your activity of conveying
the work, and under which the third party grants, to any of the
parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work
conveyed by you (or copies made from those copies), or (b) primarily
for and in connection with specific products or compilations that
contain the covered work, unless you entered into that arrangement,
or that patent license was granted, prior to 28 March 2007.

  Nothing in this License shall be construed as excluding or limiting
any implied license or other defenses to infringement that may
otherwise be available to you under applicable patent law.

  12. No Surrender of Others' Freedom.

  If conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot convey a
covered work so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you may
not convey it at all.  For example, if you agree to terms that obligate you
to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this
License would be to refrain entirely from conveying the Program.

  13. Remote Network Interaction; Use with the GNU General Public License.

  Notwithstanding any other provision of this License, if you modify the
Program, your modified version must prominently offer all users
interacting with it remotely through a computer network (if your version
supports such interaction) an opportunity to receive the Corresponding
Source of your version by providing access to the Corresponding Source
from a network server at no charge, through some standard or customary
means of facilitating copying of software.  This Corresponding Source
shall include the Corresponding Source for any work covered by version 3
of the GNU General Public License that is incorporated pursuant to the
following paragraph.

  Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU General Public License into a single
combined work, and to convey the resulting work.  The terms of this
License will continue to apply to the part which is the covered work,
but the work with which it is combined will remain governed by version
3 of the GNU General Public License.

  14. Revised Versions of this License.

  The Free Software Foundation may publish revised and/or new versions of
the GNU Affero General Public License from time to time.  Such new versions
will be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

  Each version is given a distinguishing version number.  If the
Program specifies that a certain numbered version of the GNU Affero General
Public License "or any later version" applies to it, you have the
option of following the terms and conditions either of that numbered
version or of any later version published by the Free Software
Foundation.  If the Program does not specify a version number of the
GNU Affero General Public License, you may choose any version ever published
by the Free Software Foundation.

  If the Program specifies that a proxy can decide which future
versions of the GNU Affero General Public License can be used, that proxy's
public statement of acceptance of a version permanently authorizes you
to choose that version for the Program.

  Later license versions may give you additional or different
permissions.  However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
later version.

  15. Disclaimer of Warranty.

  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

  If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely approximates
an absolute waiver of all civil liability in connection with the
Program, unless a warranty or assumption of liability accompanies a
copy of the Program in return for a fee.

                     END OF TERMS AND CONDITIONS

            How to Apply These Terms to Your New Programs

  If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.

  To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

Also add information on how to contact you by electronic and paper mail.

  If your software can interact with users remotely through a computer
network, you should also make sure that it provides a way for users to
get its source.  For example, if your program is a web application, its
interface could display a "Source" link that leads users to an archive
of the code.  There are many ways you could offer source, and different
solutions will be better for different programs; see section 13 for the
specific requirements.

  You should also get your employer (if you work as a programmer) or school,
if any, to sign a "copyright disclaimer" for the program, if necessary.
For more information on this, and how to apply and follow the GNU AGPL, see
<http://www.gnu.org/licenses/>.

EOL
  );
}


sub AddThousandsSeparators ($$$)
{
  my $str          = "$_[0]";  # Just in case, avoid converting any possible integer type to a string several times
                               # in the loop below, so just do it once at the beginnig.

  my $grouping     = $_[1];  # We are only using a single grouping value, but the locale information can actually have several.
  my $thousandsSep = $_[2];

  my $res = "";
  my $i;

  for ( $i = length( $str ) - $grouping; $i > 0; $i -= $grouping )
  {
    $res = $thousandsSep . substr( $str, $i, $grouping ) . $res;
  }

  return substr( $str, 0, $grouping + $i ) . $res;
}

# This is for manually testing of AddThousandsSeparators().
if ( FALSE )
{
  write_stdout( AddThousandsSeparators( "", 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 1, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 12, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 123, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 1234, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 12345, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 123456, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 1234567, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 12345678, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 123456789, 3, "," ) . "\n" );
  write_stdout( AddThousandsSeparators( 1234567890, 3, "," ) . "\n" );

  exit 0;
}


# Arguments: pastEpochSec, pastEpocUs, futureEpochSec, futureEpochUs

sub CalculateTimeDeltaUs ($$$$)
{
  use integer;
  return ( $_[2] - $_[0] ) * 1000 * 1000 + $_[3] - $_[1];
}


# ----------- Global variables -----------

my $g_thousandsSep;
my $g_decimalSep;
my $g_grouping;

my $g_showMicroseconds = FALSE;
my $g_noHints = FALSE;


# ----------- Script-specific constants and routines -----------

sub signal_handler
{
  my $signalName = shift;


  # We are not doing anything relevant here at the moment (no clean-up work), so we could
  # just avoid registering this signal handler if the user does not want any hints,
  # and just let the signal kill the process straight away.

  if ( not $g_noHints )
  {
    write_stdout( "\n$Script: Terminating upon reception of signal $signalName.\n" );
  }


  # Kill ourselves with the same signal. This is the recommended way of terminating
  # upon reception of a signal, after doing any clean-up work. Otherwise,
  # the parent process has no way of knowing that this process actually terminated
  # because a particular signal was received.

  $SIG{ $signalName } = "DEFAULT";

  if ( 1 != kill( $signalName, $$ ) )
  {
    write_stderr( "\n$Script: Error resending received signal $signalName to itself.\n" );
    exit( EXIT_CODE_FAILURE );
  }


  # This gets a bit tricky now. We expect that the script has killed itself with the
  # code above, but that does not happen immediately with Perl. It may have
  # to do with the "deferred" signal handling implementation from Perl 5.8.0,
  # or maybe because we are still inside a Perl signal handler, I do not really know.
  # I have another Perl script that kills itself with the same signal later,
  # outside the signal handler, and execution stops immediately.
  # But in this signal handler, any code below is still executed.
  #
  # Therefore, we cannot print an error message here, because it would always get printed,
  # even if this process does end up getting killed by the signal.
  # But if killing itself fails, we do not want the script to carry on.
  # The compromise seems to be the exit() call below. If killing itself succeeds,
  # the exit() call seems to have no effect. However, if killing itself fails,
  # exit() does run and prevents this process from running further.

  if ( FALSE )
  {
    write_stderr( "\n$Script: Cannot kill itself with signal $signalName, terminating now.\n" );
  }

  exit( EXIT_CODE_FAILURE );
}


sub UsValueToStr ($$)
{
  my $us           = $_[0];
  my $secondsWidth = $_[1];

  use integer;

  if ( $g_showMicroseconds )
  {
    return sprintf( "%${secondsWidth}s%s%03d%s%03d",
                    AddThousandsSeparators( $us / 1000 / 1000, $g_grouping, $g_thousandsSep ),
                    $g_decimalSep,
                    ( $us / 1000 ) % 1000,
                    $g_thousandsSep,
                    $us % 1000 );
  }
  else
  {
    return sprintf( "%${secondsWidth}s%s%03d",
                    AddThousandsSeparators( $us / 1000 / 1000, $g_grouping, $g_thousandsSep ),
                    $g_decimalSep,
                    ( $us / 1000 ) % 1000 );
  }
}


# ----------- Main routine -----------

sub main ()
{
  my $arg_help     = 0;
  my $arg_h        = 0;
  my $arg_help_pod = 0;
  my $arg_version  = 0;
  my $arg_license  = 0;
  my $arg_pauseDetection;

  Getopt::Long::Configure( "no_auto_abbrev",  "prefix_pattern=(--|-)", "no_ignore_case", "require_order" );

  my $result = GetOptions(
                 'help'      =>  \$arg_help,
                 'h'         =>  \$arg_h,
                 'help-pod'  =>  \$arg_help_pod,
                 'version'   =>  \$arg_version,
                 'license'   =>  \$arg_license,

                 'show-microseconds' => \$g_showMicroseconds,
                 'no-hints'          => \$g_noHints,
                 'pause-detection=f' => \$arg_pauseDetection,
               );

  if ( not $result )
  {
    # GetOptions has already printed an error message.
    return EXIT_CODE_FAILURE;
  }

  if ( $arg_help || $arg_h )
  {
    print_help_text();
    return EXIT_CODE_SUCCESS;
  }

  if ( $arg_help_pod )
  {
    write_stdout( "This file is written in Perl's Plain Old Documentation (POD) format\n" );
    write_stdout( "and has been generated with option --help-pod .\n" );
    write_stdout( "Run the following Perl commands to convert it to HTML or to plain text for easy reading:\n" );
    write_stdout( "\n" );
    write_stdout( "  pod2html README.pod >README.html\n" );
    write_stdout( "  pod2text README.pod >README.txt\n" );
    write_stdout( "\n\n" );
    write_stdout( get_pod_from_this_script() );
    write_stdout( "\n" );
    return EXIT_CODE_SUCCESS;
  }

  if ( $arg_version )
  {
    write_stdout( "$Script version " . SCRIPT_VERSION . "\n" );
    return EXIT_CODE_SUCCESS;
  }

  if ( $arg_license )
  {
    write_stdout( get_license_text() );
    return EXIT_CODE_SUCCESS;
  }

  if ( not $Config{ use64bitint } )
  {
    die "This script requires a Perl interpreter with 64-bit integer support (see build flag USE_64_BIT_INT).\n"
  }

  my $pauseDetectionUs;

  if ( defined( $arg_pauseDetection ) )
  {
    $pauseDetectionUs = $arg_pauseDetection * ( 1000 * 1000 );

    if ( $pauseDetectionUs != 0 && $pauseDetectionUs < 1 )
    {
      die "The minimum duration for --pause-detection is 0.000001 s (1 us).\n";
    }

    # We do not really need floating point, and integers are generally faster.
    $pauseDetectionUs = int( $pauseDetectionUs );
  }
  else
  {
    $pauseDetectionUs = DEFAULT_PAUSE_MS * 1000;  # This is the documented default.
  }

  my $isStdin;
  my $filename;

  if ( scalar( @ARGV ) == 0 )
  {
    $isStdin = TRUE;
    $filename = "-";  # Not really needed, but just in case.
  }
  elsif ( scalar( @ARGV ) == 1 )
  {
    $filename = $ARGV[0];
    $isStdin = ( $filename eq "-" );
  }
  else
  {
    die "Invalid number of command-line arguments. Run this tool with the --help option for usage information.\n";
  }


  my $localeValues = POSIX::localeconv();

  $g_thousandsSep = $localeValues->{ 'thousands_sep' } || ',';
  $g_decimalSep   = $localeValues->{ 'decimal_point' } || '.';

  my $localeGrouping = $localeValues->{ 'grouping' };

  my @allGroupingValues;

  if ( $localeGrouping )
  {
    @allGroupingValues = unpack( "C*", $localeGrouping );
  }
  else
  {
    @allGroupingValues = ( 3 );
  }

  # We are simplifying here by only taking the first grouping value.
  $g_grouping = $allGroupingValues[ 0 ];


  $SIG{INT}  = \&signal_handler;
  $SIG{HUP}  = \&signal_handler;


  my $deltaSecondsWidth = 1;  # We do not need any column alignment, so that is why the value is 1 at the moment.

  my $file;

  if ( $isStdin )
  {
    $file = *STDIN;
  }
  else
  {
    if ( FALSE )
    {
      write_stdout( "Reading from file \"$filename\"...\n" );
    }

    open( $file, '<:raw', $filename )
      or die "Cannot open file \"$filename\": $!\n";

    binmode( $file )  # Avoids CRLF conversion.
      or die "Cannot access file \"$filename\" in binary mode: $!\n";
  }


  my $initialSecondsSinceEpoch;
  my $initialMicroseconds;

  my $lastSecondsSinceEpoch;
  my $lastMicroseconds;

  my $lastWrittenByte = "";

  my $isFirstTime = TRUE;

  use constant SOME_ARBITRARY_BUFFER_SIZE => 16 * 1024;

  my $readBuffer;

  # Buffering is important for performance. We manually flush just once after every sysread().
  STDOUT->autoflush( 0 );

  for ( ; ; )
  {
    # Alternative function read() waits until the specified number of bytes arrives, which is not what we want.
    my $readByteCount = sysread( $file, $readBuffer, SOME_ARBITRARY_BUFFER_SIZE );

    if ( not defined $readByteCount )
    {
      if ( $isStdin )
      {
        die "Error reading from stdin: $!\n";
      }
      else
      {
        die "Error reading from file \"$filename\": $!\n";
      }
    }

    if ( $readByteCount == 0 )
    {
      if ( not $g_noHints )
      {
        my $msg = "";

        if ( ! $isFirstTime && $lastWrittenByte ne "\n" )
        {
          $msg .= "\n";
        }

        $msg .= "Terminating upon reaching end of file.\n";

        write_stdout( $msg );
      }

      last;
    }

    if ( FALSE )
    {
      write_stdout( "Number of bytes read: $readByteCount\n" );
    }

    my ( $currentSecondsSinceEpoch, $currentMicroseconds ) = Time::HiRes::gettimeofday;

    my $timeDeltaUs;

    if ( $isFirstTime )
    {
      $initialSecondsSinceEpoch = $currentSecondsSinceEpoch;
      $initialMicroseconds      = $currentMicroseconds;

      $timeDeltaUs              = 0;
    }
    else
    {
      $timeDeltaUs = CalculateTimeDeltaUs( $lastSecondsSinceEpoch, $lastMicroseconds, $currentSecondsSinceEpoch, $currentMicroseconds );
    }

    if ( $pauseDetectionUs != 0 &&
         $pauseDetectionUs <= $timeDeltaUs )
    {
      my $pauseMsg = "";

      if ( $lastWrittenByte ne "\n" )
      {
        # These hints may be a little confusing if the pause comes just before the final <CR>,
        # but I do not think that it is worth writing a special case for this scenario.
        $pauseMsg .= PAUSE_INSIDE_LINE_HINT_END . "\n";
      }

      $pauseMsg .= "\n";

      $pauseMsg .= "< pause of " . UsValueToStr( $timeDeltaUs, $deltaSecondsWidth ) . " seconds >" . "\n";

      $pauseMsg .= "\n";

      if ( $lastWrittenByte ne "\n" )
      {
        $pauseMsg .= PAUSE_INSIDE_LINE_HINT_BEGIN;
      }

      write_stdout( $pauseMsg );
    }

    write_stdout( $readBuffer );

    $lastWrittenByte = substr( $readBuffer, -1 );

    flush_stdout();

    $lastSecondsSinceEpoch = $currentSecondsSinceEpoch;
    $lastMicroseconds      = $currentMicroseconds;
    $isFirstTime           = FALSE;
  }

  if ( ! $isStdin )
  {
    $file->close() or
      die "Cannot close file \"$filename\": $!\n";
  }

  return EXIT_CODE_SUCCESS;
}


eval
{
  exit main();
};

my $errorMessage = $@;

# We want the error message to be the last thing on the screen,
# so we need to flush the standard output first.
STDOUT->flush();

print STDERR "\nError running '$Script': $errorMessage";

exit EXIT_CODE_FAILURE;