CountdownTimer.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

A countdown timer, like a kitchen timer for your perfect cup of tea.

=head1 RATIONALE

I could not find a countdown timer I really liked, so I decided to roll my own.

This is what the output looks like:

  $ ./CountdownTimer.pl "1m 30s"
  Start time: 2020-10-04 16:45:00
  Countdown duration: 1 minute, 30 seconds (90 seconds)

  Countdown: 01:25  Finish time: 16:46:30

The remaining time on the last output line is updated as time passes.

The timing method is not a simplistic I<< sleep( 1 second ) >> between updates, but is based
either on the real-time clock or on CLOCK_MONOTONIC (a kind of uptime), see option I<--method> further below.

=head1 USAGE

 perl SCRIPT_NAME [options] [--] [duration]

If no duration is specified, the user will be prompted for one.

The duration is a single command-line argument. If it contains spaces and you are running this script from the shell,
you will need to quote the duration so that it gets passed as a single argument.

The maximum duration is 10 years.

Possible duration formats are:

=over

=item *

An natural number like 123 is interpreted as a number of seconds.

=item *

A digital clock like 1:02 or 01:02 is interpreted as minutes and seconds (62 seconds in this example).

=item *

A digital clock like 1:02:03 or 01:02:03 is interpreted as hours, minutes and seconds (3,723 seconds in this example).

=item *

A condensed expression like 1m2s (62 seconds in this example).

=item *

A rather flexible and tolerant human expression like "2 weeks, 1 days, 8 hour, and 3 minutes and 2 secs", which yields 1,324,982 seconds in this example.

=back

If you want to run some action after the countdown has finished, you can chain commands in your shell like this:

 ./SCRIPT_NAME '3 seconds' && zenity --info --text 'Countdown finished.'

See also script I<< DesktopNotification.sh >> in the same repository as this one.

You can use script I<< background.sh >> (also in the same repository as this script) for notification purposes too like this:

  background.sh --no-prio --filter-log -- ./SCRIPT_NAME '3 seconds'

If you create a desktop icon with the following command, a new console window will open up
and prompt you for the timer duration:

  /some/path/run-in-new-console.sh --console-title='Countdown Timer' --console-icon=clock -- '/some/path/SCRIPT_NAME && /some/path/DesktopNotification.sh "Countdown finished."'

You will find I<< run-in-new-console.sh >> in the same repository as this script.

=head1 OPTIONS

=over

=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.

=item *

B<--method=<method name>>

The method name can be either B< monotonic >, or B<< real time >> (B<< realtime >> and B<< real-time >> work too).
The name is case insensitive. The default is I<< real time >>.

Each timing method is explained in its own section further below.

=item *

B<--self-test>

Runs some internal self-tests.

=back

=head1 TIMING METHOD 'REAL TIME'

This is the default timing method, see option I<< --method=<method name> >>S< >.

A 10-minute countdown started at 14:00 will finish at 14:10.

If you (or something like NTP) decide to adjust the clock in the meantime, perhaps because the clock was runnnig fast,
your countdown duration will no longer be the desired 10 minutes.

Clock changes due to sommer time will not affect the countdown duration, because this script uses UTC internally.

If your laptop goes to sleep, this script will pause executing, so, if the countdown expires during the sleep period,
the script will not actually exit until the laptop wakes up. Therefore, by allowing your laptop to sleep
during a countdown, you risk missing the countdown deadline (you will get notified too late),
which will make your black tee unpalatable.

The countdown seconds display will not actually update in sync with the real-time clock seconds, and
the countdown finish time will usually fall between real-time clock seconds. This is because
I could not find a way to tick this script in sync with the real-time clock.

=head1 TIMING METHOD 'MONOTONIC'

You can use this timing method with option I<< --method=monotonic >>S< >.

The script will then use CLOCK_MONOTONIC (a kind of uptime).
This means that the countdown timer is not synchronised
with the real-time clock, which has advantages and disadvantages:

=over

=item *

The countdown timer is not affected by any real-time clock changes.

The ETA (estimated time of arrival) on the progress message does get updated if necessary,
but that does not affect the overall countdown duration.

There may still be some external interference with the monotonic clock. For example, the Linux documentation
states some differences between CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW in this respect.

=item *

The real-time clock is often synchronised over NTP, but the internal monotonic clock is usually not.

Therefore, the accuracy of the countdown timer depends on the accuracy of the internal clock.
Clock drifting may become noticeable for long countdown periods.

=item *

The countdown seconds display will not update in sync with the real-time clock seconds.

The countdown finish time will usually fall between real-time clock seconds.

=item *

The timer will not count whilst the computer is asleep.

Let's say that you are using this script to remind you when your washing machine has finished.
If your laptop goes to sleep, you will miss the notification. When the laptop wakes up,
it will countinue counting exactly where it was, so the washing machine may have already finished.
Even if your laptop slept just 15 minutes, the countdown timer will be delayed by those 15 minutes,
which is also not ideal, because your washing machine will not actually be delayed.

This script could switch from CLOCK_MONOTONIC to the Linux-specific CLOCK_BOOTTIME,
so that the timer does get adjusted after waking up. That is of course assuming
that the script is running on Linux. And if Perl's Time::HiRes module actually supported CLOCK_BOOTTIME.
Moreover, it looks like CLOCK_BOOTTIME is only available on the Linux syscall, not even via glibc,
further complicating matters. This change would not be enough to wake the computer up should the
timer reach zero while asleep. And whether automatically waking up is desirable, is yet another question.

=back

=head1 EXIT CODE

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

=head1 POSSIBLE IMPROVEMENTS

Many things could be improved, like adding built-in visual notifications or using a GUI tool like I<< yad >>
for prompting and progress indication.

=head1 BREAKING CHANGE AFTER VERSION 1.07

Version 1.07 only implemented the I< monotonic > method, and version 2.00 introduced the alternative I< real time >
method and made it the default. Therefore, the default timing behaviour has changed between those two versions.

=head1 FEEDBACK

Please send feedback to rdiezmail-tools at yahoo.de

=head1 LICENSE

Copyright (C) 2019-2023 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 Getopt::Long;
use Pod::Usage;
use Term::ReadLine;
use Time::HiRes qw( CLOCK_MONOTONIC CLOCK_REALTIME );
use POSIX;


use constant SCRIPT_VERSION => "2.02";

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;


# ----------- 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 ( not defined STDOUT->flush() )
  {
    # The documentation does not say whether $! is set in case of error.
    die "Error flushing sdtout.\n";
  }
}


#------------------------------------------------------------------------
#
# Removes leading and trailing blanks.
#

sub trim_blanks ( $$ )
{
  my $retstr = shift;
  my $whitespaceExpression = shift;

  # POSSIBLE OPTIMISATION: Removing blanks could perhaps be done faster with transliterations (tr///).

  # Strip leading blanks.
  $retstr =~ s/\A$whitespaceExpression*//;

  # Strip trailing blanks.
  $retstr =~ s/$whitespaceExpression*\z//;

  return $retstr;
}


sub build_message_with_regex_pos_arrays ()
{
  my $msg = "";

  $msg .= "Array \@- with " . scalar( @- ) . " element(s): \n";

  foreach my $p ( @- )
  {
    $msg .= "- " . ( defined( $p ) ? "$p" : "<undefined>" ) . "\n";
  }

  $msg .= "Array \@+ with " . scalar( @+ ) . " element(s): \n";

  foreach my $p ( @+ )
  {
    $msg .= "- " . ( defined( $p ) ? "$p" : "<undefined>" ) . "\n";
  }

  return $msg;
}


sub divide_round_up ( $$ )
{
  my $dividend = shift;
  my $divisor  = shift;

  use integer;

  return ( $dividend + $divisor - 1 ) / $divisor;
}


#------------------------------------------------------------------------
#
# 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;

  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

 Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.

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  The licenses for most software and other practical works are designed
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  When we speak of free software, we are referring to freedom, not
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incorporate.  Many developers of free software are heartened and
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software used on network servers, this result may fail to come about.
The GNU General Public License permits making a modified version and
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  The GNU Affero General Public License is designed specifically to
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  All other non-permissive additional terms are considered "further
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  9. Acceptance Not Required for Having Copies.

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  11. Patents.

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  12. No Surrender of Others' Freedom.

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  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
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  14. Revised Versions of this License.

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                     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.

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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
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    (at your option) any later version.

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    but WITHOUT ANY WARRANTY; without even the implied warranty of
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    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
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Also add information on how to contact you by electronic and paper mail.

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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
  );
}


# ----------- Script-specific code -----------

sub parse_clock_part ( $$$ )
{
  my $component     = shift;
  my $componentName = shift;
  my $maxValue      = shift;

  my $v = int( $component );

  if ( $v > $maxValue )
  {
    die "The number of $componentName cannot be greater than $maxValue.\n";
  }

  return $v;
}


# We must impose some limit on the duration. Otherwise, we will run into numeric overflows
# and all sorts of places will start complaining.
#
# The following yields and 316,224,000 is equivalent to 10 leap years.
# It is 1 digit shorter than the maximum 32-bit signed integer number, which is 2,147,483,647.
#
# The Perl interpreter normally uses 64-bit integers, but the wait loop uses floating-point numbers.
# If you pass a huge number of seconds, the floating-point precision may not be enough
# to guarantee a smooth progress display in seconds, or even an accurate wait time.

use constant MAX_DURATION => 10 * 366 * 24 * 60 * 60;

use constant MAX_DURATION_LEN => length( "@{[ MAX_DURATION ]}" );


sub parse_str_as_time_number ( $ )
{
  my $valueAsStr = shift;

  if ( length( $valueAsStr ) > MAX_DURATION_LEN )
  {
    die "The time value '$valueAsStr' is too big.\n";
  }

  my $v = int( $valueAsStr );

  if ( $v > MAX_DURATION )
  {
    die "The time value '$valueAsStr' is too big.\n";
  }

  return $v;
}


my $whitespace = "[\x20\x09]";  # Whitespace is only a space or a tab.


sub parse_time_value ( $ )
{
  my $humanDuration = shift;

  my $originalDuration = $$humanDuration;

  # Assume that there is no whitespace to the left. The string must begin with a natural number.

  if ( not $$humanDuration =~ m/\A\d+/oas )
  {
    die "A duration component does not start with a valid value.\n";
  }

  if ( scalar( @- ) != 1 ||
       scalar( @+ ) != 1 )
  {
    die "Internal error parsing the countdown duration: \n" . build_message_with_regex_pos_arrays();
  }

  my $beginPos = $-[ 0 ];
  my $endPos   = $+[ 0 ];

  my $part = substr( $$humanDuration, $beginPos, $endPos - $beginPos );

  my $value = parse_str_as_time_number( $part );

  $$humanDuration = substr( $$humanDuration, $endPos );

  if ( FALSE )
  {
    write_stdout( "\nTime value parsing result:\n" );
    write_stdout( "str     : <$originalDuration>\n" );
    write_stdout( "beginPos: $beginPos\n" );
    write_stdout( "endPos  : $endPos\n" );
    write_stdout( "Value   : $value\n" );
    write_stdout( "Rest    : <$$humanDuration>\n" );
  }

  return $value;
}


# Define time units up to a week.
# Months and years are problematic because they are ambiguous.
# One month can be 28 to 31 days long, and one year 365 or 366 days.

my %timeUnits = ( map( ( $_ ,                1 ), qw( s second seconds sec secs ) ),
                  map( ( $_ ,               60 ), qw( m minute minutes min mins ) ),
                  map( ( $_ ,          60 * 60 ), qw( h hr hrs hour hours       ) ),
                  map( ( $_ ,     24 * 60 * 60 ), qw( d day days                ) ),
                  map( ( $_ , 7 * 24 * 60 * 60 ), qw( w week weeks              ) ) );

sub parse_time_unit ( $ )
{
  my $humanDuration = shift;

  my $originalDuration = $$humanDuration;

  # Discard any whitespace to the left. Then read a word. Discard any spaces to the right.

  if ( not $$humanDuration =~ m/\A$whitespace*([a-z]+)$whitespace*/oasi )
  {
    die "A duration component has no valid time unit.\n";
  }

  if ( scalar( @- ) != 2 ||
       scalar( @+ ) != 2 )
  {
    die "Internal error parsing the countdown duration: \n" . build_message_with_regex_pos_arrays();
  }

  my $unitBeginPos = $-[ 1 ];
  my $unitEndPos   = $+[ 1 ];

  my $unit = substr( $$humanDuration, $unitBeginPos, $unitEndPos - $unitBeginPos );

  my $wholeRegexMatchEndPos = $+[ 0 ];

  $$humanDuration = substr( $$humanDuration, $wholeRegexMatchEndPos );

  if ( FALSE )
  {
    write_stdout( "\nTime unit parsing result:\n" );
    write_stdout( "str     : <$originalDuration>\n" );
    write_stdout( "beginPos: $unitBeginPos\n" );
    write_stdout( "endPos  : $unitEndPos\n" );
    write_stdout( "Unit    : $unit\n" );
    write_stdout( "Rest    : <$$humanDuration>\n" );
    write_stdout( build_message_with_regex_pos_arrays() );
  }

  my $lowercaseUnit = lc( $unit );

  my $numberOfSecondsForUnit = $timeUnits{ $lowercaseUnit };

  if ( not defined $numberOfSecondsForUnit )
  {
    die "Invalid time unit '$unit'.\n";
  }

  return $numberOfSecondsForUnit;
}


sub parse_time_separator ( $ )
{
  my $humanDuration = shift;

  my $originalDuration = $$humanDuration;

  # Assume that there is no whitespace to the left.
  # Read a separator. Discard any spaces to the right.
  #
  # Separator examples:
  #   1m,2s
  #   1m, 2s
  #   1m and 2s
  #   1m,and 2s
  #   1m, and 2s

  my $matchResultComma = $$humanDuration =~
      m/

        \A            # Begin of string.

        ,             # A comma.

        $whitespace*  # Any whitespace afterwards.

       /xoasi;

  if ( $matchResultComma )
  {
    if ( scalar( @- ) != 1 ||
         scalar( @+ ) != 1 )
    {
      die "Internal error parsing the countdown duration: \n" . build_message_with_regex_pos_arrays();
    }

    my $wholeRegexMatchEndPos = $+[ 0 ];

    $$humanDuration = substr( $$humanDuration, $wholeRegexMatchEndPos );
  }


  my $matchResultAnd = $$humanDuration =~
      m/

         \A                  # Begin of string.

         and                 # The word 'and'.

         (?:$whitespace+|\z) # Whitespace afterwards. At least one whitespace character must be there.
                             # Or end of string. Do not capture this expression.

       /xoasi;

  if ( $matchResultAnd )
  {
    if ( scalar( @- ) != 1 ||
         scalar( @+ ) != 1 )
    {
      die "Internal error parsing the countdown duration: \n" . build_message_with_regex_pos_arrays();
    }

    my $wholeRegexMatchEndPos = $+[ 0 ];

    $$humanDuration = substr( $$humanDuration, $wholeRegexMatchEndPos );
  }


  my $wasSomethingMatched = $matchResultComma || $matchResultAnd;

  if ( $wasSomethingMatched )
  {
    if ( FALSE )
    {
      write_stdout( "\nSeparator parsing result:\n" );
      write_stdout( "str     : <$originalDuration>\n" );
      write_stdout( "Rest    : <$$humanDuration>\n" );
      write_stdout( build_message_with_regex_pos_arrays() );
    }
  }

  return $wasSomethingMatched;
}


sub parse_human_duration ( $ )
{
  my $humanDuration = shift;


  # If it is an integer number, treat is as a number of seconds.

  if ( $humanDuration =~ m/\A\d+\z/oas )
  {
    return parse_str_as_time_number( $humanDuration );
  }

  my @clock4Parts = $humanDuration =~ m/\A(\d\d?):(\d\d)\z/oas;

  if ( scalar( @clock4Parts ) > 0 )
  {
    my $minutes = parse_clock_part( $clock4Parts[0], "minutes", 59 );
    my $seconds = parse_clock_part( $clock4Parts[1], "seconds", 59 );

    return $minutes * 60 + $seconds;
  }


  my @clock6Parts = $humanDuration =~ m/\A(\d\d?):(\d\d):(\d\d)\z/oas;

  if ( scalar( @clock6Parts ) > 0 )
  {
    my $hours   = parse_clock_part( $clock6Parts[0], "hours"  , 23 );
    my $minutes = parse_clock_part( $clock6Parts[1], "minutes", 59 );
    my $seconds = parse_clock_part( $clock6Parts[2], "seconds", 59 );

    return $hours * 60 * 60 + $minutes * 60 + $seconds;
  }


  my $wasLastElementASeparator = FALSE;

  my $numberOfSeconds = 0;

  for ( ; ; )
  {
    my $timeValue = parse_time_value( \$humanDuration );

    my $componentSeconds = parse_time_unit( \$humanDuration );

    my $maxComponentValue = divide_round_up( MAX_DURATION, $componentSeconds );

    if ( FALSE )
    {
      write_stdout( "Max component value: $maxComponentValue\n" );
    }

    if ( $timeValue > $maxComponentValue )
    {
      die "Time component '$timeValue' is too big.\n";
    }

    $numberOfSeconds += $timeValue * $componentSeconds;

    if ( $numberOfSeconds > MAX_DURATION )
    {
      die "The countdown duration is too big.\n";
    }

    $wasLastElementASeparator = parse_time_separator( \$humanDuration );

    if ( $humanDuration eq "" )
    {
      last;
    }
  }

  if ( $wasLastElementASeparator )
  {
    die "Missing duration component after last separator.\n";
  }

  return $numberOfSeconds;
}


my $g_selfTestCaseNumber;

sub parse_human_duration_test_case ( $$ )
{
  my $humanDuration           = shift;
  my $expectedNumberOfSeconds = shift;

  write_stdout( "Test " . ++$g_selfTestCaseNumber . ".\n" );

  my $result = parse_human_duration( $humanDuration );

  if ( $result != $expectedNumberOfSeconds )
  {
    die "Test case failed:\n" .
        "- Human duration: $humanDuration\n" .
        "- Result        : $result seconds\n" .
        "- Expected      : $expectedNumberOfSeconds seconds\n";
  }
}


sub self_test ()
{
  write_stdout( "Testing the human duration parser...\n" );

  $g_selfTestCaseNumber = 0;

  parse_human_duration_test_case( "0", 0 );
  parse_human_duration_test_case( "123", 123 );

  parse_human_duration_test_case(  "1:02", 62 );
  parse_human_duration_test_case( "01:02", 62 );

  parse_human_duration_test_case(  "1:02:03", 3723 );
  parse_human_duration_test_case( "01:02:03", 3723 );

  parse_human_duration_test_case( "1s", 1 );
  parse_human_duration_test_case( "12seconds", 12 );
  parse_human_duration_test_case( "123 seconds", 123 );
  parse_human_duration_test_case( "123 seconds ", 123 );

  parse_human_duration_test_case( "456 sEconDs", 456 );

  parse_human_duration_test_case( "1m2s", 62 );
  parse_human_duration_test_case( "1m 2s", 62 );

  parse_human_duration_test_case( "1m,2s", 62 );
  parse_human_duration_test_case( "1m, 2s", 62 );
  parse_human_duration_test_case( "1m ,2s", 62 );
  parse_human_duration_test_case( "1m , 2s", 62 );
  parse_human_duration_test_case( "1m  ,   2s", 62 );

  parse_human_duration_test_case( "1m and 2s", 62 );
  parse_human_duration_test_case( "1m  and   2s", 62 );

  parse_human_duration_test_case( "1m,and 2s", 62 );
  parse_human_duration_test_case( "1m, and 2s", 62 );
  parse_human_duration_test_case( "1m ,and 2s", 62 );
  parse_human_duration_test_case( "1m , and 2s", 62 );

  parse_human_duration_test_case( "2 minutes and 2 seconds", 122 );

  parse_human_duration_test_case( "3 hours and 2 seconds", 10802 );

  parse_human_duration_test_case( "2 weeks, 3 days, 8 hours, 3 minutes", 1497780 );

  parse_human_duration_test_case( "2 weeks, 3 days, 8 hours, 3 minutes and 2 secs", 1497782 );

  # This is the example in the usage documentation:
  parse_human_duration_test_case( "2 weeks, 1 days, 8 hour, and 3 minutes and 2 secs", 1324982 );

  parse_human_duration_test_case( "1 week", 604800 );


  write_stdout( "\nTesting the elapsed time formatter...\n" );

  self_test_format_human_friendly_duration();


  write_stdout( "\nTesting the countdown time formatter...\n" );

  self_test_format_countdown_time_left();
}


sub update_progress_line ( $$ )
{
  my $newProgressLineText = shift;
  my $lastProgressLineLen = shift;

  my $str = $newProgressLineText;

  # If a long string is replaced with a short one, the first time that this happen
  # the cursor will be further to the right as usual. This effect will last for one second,
  # until the next update.
  # We could prevent it from happening in the following ways:
  # - If the new string is shorter, delete everything with spaces, go back again,
  #   and print the new line.
  #   This would be inefficient.
  # - Make sure that all strings are of the same length, by always padding up with spaces.
  #   But then the cursor will permanently be further to the right as necessary.
  #   And it would be inefficient too.
  #
  # Alternative: Some terminals support the \033[K "erase in line" escape sequence:
  #
  #   ESC [ Pn K
  #
  # Where  Pn = None or 0   Erases from cursor to end of line.
  #             1           Erases from beginning of line to cursor.
  #             2           Erases the entire line.
  #
  # For example, this clears everything on the line, regardless of cursor position:
  #
  #   echo -e "\033[2K"
  #
  # Command "tput el" can output this escape sequence. For example:
  #
  #   ceol=$(tput el)  # el: Clear to end of line
  #   echo -ne "blah blah... \r${ceol}foobar"


  if ( length( $newProgressLineText ) < $$lastProgressLineLen )
  {
    $str .= ' ' x ( $$lastProgressLineLen - length( $newProgressLineText ) );
  }

  # Output one space more, so that an eventual console cursor is not right
  # next to the last character.
  write_stdout( "\r$str " );

  flush_stdout();

  $$lastProgressLineLen = length( $newProgressLineText );
}


my $g_thousandsSep;
my $g_grouping;

sub init_locale_info ()
{
  my $localeValues = POSIX::localeconv();

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

  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 ];
}


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;
}


sub plural_s ( $ )
{
  return ( $_[0] == 1 ) ? "" : "s";
}


use constant SECONDS_IN_MINUTE => 60;
use constant SECONDS_IN_HOUR   => 60 * SECONDS_IN_MINUTE;
use constant SECONDS_IN_DAY    => 24 * SECONDS_IN_HOUR;
use constant SECONDS_IN_WEEK   =>  7 * SECONDS_IN_DAY;


#------------------------------------------------------------------------
#
# Formats a duration as a human-friendly string, with hours, minutes, etc.
#

sub format_human_friendly_duration ( $ )
{
  use integer;

  my $totalSeconds = shift;  # Number of seconds as an integer.

  if ( $totalSeconds < 0 )
  {
    die "Invalid number of seconds.\n";
  }

  if ( $totalSeconds < SECONDS_IN_MINUTE )
  {
    return sprintf( '%d second%s', $totalSeconds, plural_s( $totalSeconds ) );
  }

  # At this point, the message will not consist of just a number of seconds.
  # The total number of seconds will be appended to the message inside parenthesis.

  my $seconds = $totalSeconds;

  my $minutes = $seconds  / 60;
  $seconds    = $seconds  % 60;

  # Possible optimisation: Do not consider higher units if the number of minutes <= 59,
  #                        and the same later on for hours etc.

  my $hours   = $minutes  / 60;
  $minutes    = $minutes  % 60;

  my $days    = $hours    / 24;
  $hours      = $hours    % 24;

  my $weeks   = $days     /  7;
  $days       = $days     %  7;

  # Months are problematic in a duration, because not all months have the same number of days.


  my @messageComponents;

  if ( $weeks > 0 )
  {
    my $formattedWeeks = AddThousandsSeparators( $weeks, $g_grouping, $g_thousandsSep );

    push @messageComponents, sprintf( '%s week%s', $formattedWeeks, plural_s( $weeks ) );
  }

  if ( $days > 0 )
  {
    push @messageComponents, sprintf( '%d day%s', $days, plural_s( $days ) );
  }

  if ( $hours > 0 )
  {
    push @messageComponents, sprintf( '%d hour%s', $hours, plural_s( $hours ) );
  }

  if ( $minutes > 0 )
  {
    push @messageComponents, sprintf( '%d minute%s', $minutes, plural_s( $minutes ) );
  }

  if ( $seconds > 0 )
  {
    push @messageComponents, sprintf( '%d second%s', $seconds, plural_s( $seconds ) );
  }


  my $messageComponentCount = scalar( @messageComponents );
  my $message;

  if ( $messageComponentCount < 2 )
  {
    $message = $messageComponents[ 0 ];
  }
  else
  {
    my $lastMessageComponent = pop @messageComponents;

    $messageComponents[ $messageComponentCount - 2 ] .= " and " . $lastMessageComponent;

    $message = join( ", ", @messageComponents );
  }

  return $message . " (" . AddThousandsSeparators( $totalSeconds, $g_grouping, $g_thousandsSep ) . " seconds)";
}


my $g_fhfdTestCaseNumber;

sub fhfd_test ( $ $ )
{
  my $numberOfSeconds = shift;
  my $expectedResult  = shift;

  write_stdout( "Test " . ++$g_fhfdTestCaseNumber . ".\n" );


  my $saved_thousandsSep = $g_thousandsSep;
  my $saved_grouping     = $g_grouping;

  $g_thousandsSep = ",";
  $g_grouping     = 3;

  my $result;

  eval
  {
    $result = format_human_friendly_duration( $numberOfSeconds );
  };

  my $errorMessage = $@;

  $g_thousandsSep = $saved_thousandsSep;
  $g_grouping     = $saved_grouping;

  if ( $errorMessage )
  {
    die $errorMessage;
  }


  if ( $result ne $expectedResult )
  {
    die "Test case failed:\n" .
        "- Number of seconds: $numberOfSeconds\n" .
        "- Result           : $result\n" .
        "- Expected         : $expectedResult\n";
  }
}


sub self_test_format_human_friendly_duration ( $ $ )
{
  $g_fhfdTestCaseNumber = 0;

  fhfd_test( 0, "0 seconds" );
  fhfd_test( 1, "1 second" );
  fhfd_test( 59, "59 seconds" );

  fhfd_test( SECONDS_IN_WEEK,        "1 week (604,800 seconds)" );
  fhfd_test( SECONDS_IN_WEEK * 2,    "2 weeks (1,209,600 seconds)" );
  fhfd_test( SECONDS_IN_WEEK * 1234, "1,234 weeks (746,323,200 seconds)" );

  fhfd_test( SECONDS_IN_WEEK +     SECONDS_IN_DAY, "1 week and 1 day (691,200 seconds)" );
  fhfd_test( SECONDS_IN_WEEK + 2 * SECONDS_IN_DAY, "1 week and 2 days (777,600 seconds)" );

  fhfd_test( SECONDS_IN_WEEK + SECONDS_IN_DAY + SECONDS_IN_HOUR, "1 week, 1 day and 1 hour (694,800 seconds)" );

  fhfd_test( SECONDS_IN_WEEK + SECONDS_IN_DAY + SECONDS_IN_HOUR + SECONDS_IN_MINUTE, "1 week, 1 day, 1 hour and 1 minute (694,860 seconds)" );

  fhfd_test( SECONDS_IN_WEEK + SECONDS_IN_DAY + SECONDS_IN_HOUR + SECONDS_IN_MINUTE + 3, "1 week, 1 day, 1 hour, 1 minute and 3 seconds (694,863 seconds)" );

  fhfd_test( SECONDS_IN_WEEK + SECONDS_IN_HOUR, "1 week and 1 hour (608,400 seconds)" );

  fhfd_test( SECONDS_IN_WEEK + SECONDS_IN_HOUR + 2 * SECONDS_IN_MINUTE, "1 week, 1 hour and 2 minutes (608,520 seconds)" );

  fhfd_test( SECONDS_IN_WEEK + SECONDS_IN_HOUR + 2 * SECONDS_IN_MINUTE + 3, "1 week, 1 hour, 2 minutes and 3 seconds (608,523 seconds)" );

  fhfd_test( 2 * SECONDS_IN_WEEK + 1, "2 weeks and 1 second (1,209,601 seconds)" );

  fhfd_test( SECONDS_IN_DAY, "1 day (86,400 seconds)" );

  fhfd_test( SECONDS_IN_MINUTE,     "1 minute (60 seconds)" );
  fhfd_test( SECONDS_IN_MINUTE * 5, "5 minutes (300 seconds)" );
  fhfd_test( SECONDS_IN_MINUTE + 3, "1 minute and 3 seconds (63 seconds)" );
}


sub format_countdown_time_left ( $ )
{
  use integer;

  my $totalSeconds = shift;  # Number of seconds as an integer.

  if ( $totalSeconds < 0 )
  {
    die "Invalid number of seconds.\n";
  }

  my $seconds = $totalSeconds;

  my ( $weeks, $days, $hours, $minutes, $res ) = qw/0 0 0 0 0/;

  my $separator = ',';

  ( $seconds, $minutes ) = ( $seconds % 60, $seconds / 60 ) if $seconds;
  ( $minutes, $hours   ) = ( $minutes % 60, $minutes / 60 ) if $minutes;
  ( $hours  , $days    ) = ( $hours   % 24, $hours   / 24 ) if $hours  ;
  ( $days   , $weeks   ) = ( $days    %  7, $days    /  7 ) if $days   ;

  # Only show the hours if we have more than one hour to wait.

  if ( $totalSeconds >= SECONDS_IN_HOUR )
  {
    $res = sprintf( "%02d:%02d:%02d", $hours, $minutes, $seconds );
  }
  else
  {
    $res = sprintf( "%02d:%02d", $minutes, $seconds );
  }

  $res = sprintf ( "%d day%s$separator $res" , $days , plural_s( $days  ) ) if $days or $weeks;
  $res = sprintf ( "%d week%s$separator $res", $weeks, plural_s( $weeks ) ) if          $weeks;

  return $res;
}


my $g_fctlTestCaseNumber;

sub fctl_test ( $ $ )
{
  my $numberOfSeconds = shift;
  my $expectedResult  = shift;

  write_stdout( "Test " . ++$g_fctlTestCaseNumber . ".\n" );


  my $result = format_countdown_time_left( $numberOfSeconds );

  if ( $result ne $expectedResult )
  {
    die "Test case failed:\n" .
        "- Number of seconds: $numberOfSeconds\n" .
        "- Result           : $result\n" .
        "- Expected         : $expectedResult\n";
  }
}


sub self_test_format_countdown_time_left ()
{
  $g_fctlTestCaseNumber = 0;

  fctl_test( 0, "00:00" );
  fctl_test( 1, "00:01" );
  fctl_test( SECONDS_IN_MINUTE + 2, "01:02" );

  fctl_test( SECONDS_IN_HOUR, "01:00:00" );
  fctl_test( 3 * SECONDS_IN_HOUR + 2 * SECONDS_IN_MINUTE + 1, "03:02:01" );

  fctl_test( 2 * SECONDS_IN_WEEK, "2 weeks, 0 days, 00:00:00" );

  fctl_test( 3 * SECONDS_IN_DAY, "3 days, 00:00:00" );
  fctl_test( 4 * SECONDS_IN_DAY + 3 * SECONDS_IN_HOUR + 2 * SECONDS_IN_MINUTE + 1, "4 days, 03:02:01" );
}


# %Y-%m-%d is the ISO 8601 date format.
use constant LONG_TIME_FMT => "%Y-%m-%d %H:%M:%S";

sub format_end_human_time ( $$ )
{
  my $currentHumanTime = shift;
  my $endHumanTime     = shift;

  # Only show the date if if falls on another date.

  my ( $currSec, $currMin, $currHour, $currMday, $currMon, $currYear, $currWday, $currYday, $currIsdst ) = localtime( $currentHumanTime );
  my ( $endSec , $endMin , $endHour , $endMday , $endMon , $endYear , $endWday , $endYday , $endIsdst  ) = localtime( $endHumanTime );

  my $formatStr;

  if ( $currMday != $endMday or
       $currMon  != $endMon  or
       $currYear != $endYear )
  {
    $formatStr = LONG_TIME_FMT;
  }
  else
  {
    $formatStr = "%H:%M:%S";
  }

  return POSIX::strftime( $formatStr, $endSec , $endMin , $endHour , $endMday , $endMon , $endYear , $endWday , $endYday , $endIsdst );
}


sub wait_for_next_round_second ( $ )
{
  my $timeLeft = shift;

  my $waitForTime;

  if ( $timeLeft <= 1 )
  {
    $waitForTime = $timeLeft;
  }
  else
  {
    # Wait until the next round second.
    $waitForTime = $timeLeft - int( $timeLeft );


    # If we would be waiting too little time, then we are almost on a round second,
    # but it is not clear on which side of it we are.
    #
    # Remember that a floating point calculation may deliver a negative value due to lack of precision.
    # This all would be easier if Perl's Time::HiRes did not use floating-point values for time.
    # After all, all operating systems I know return an integer (the number of milliseconds or nanoseconds).
    #
    # Maybe the system was busy, this script got no CPU time until now, and we happen to be
    # on a round second at this moment. Or Perl got very fast, and we landed exactly on the
    # next round second we were waiting for.
    #
    # The logic should be:
    # - If we are slightly on the left of a round second, we should update soon again, so that
    #   we do not miss a screen update for next round second.
    # - If we are slightly on the right of a round second, we should update again in almost 1 second.
    #
    # To be on the safe side, just update again soon. It is better to update too often than too few times.
    # The worst that would happen is that we end up updating twice per second.

    if ( $waitForTime <= 0.01 )
    {
      $waitForTime = 0.02;
    }
  }

  if ( FALSE )
  {
    write_stdout( "\nWait for: " . $waitForTime . " second(s)\n" );
  }

  Time::HiRes::sleep( $waitForTime );
}


sub countdown_monotonic ( $ )
{
  my $durationInSeconds = shift;

  my $startTime = Time::HiRes::clock_gettime( CLOCK_MONOTONIC );

  my $endTime = $startTime + $durationInSeconds;

  if ( FALSE )
  {
    write_stdout( "startTime: $startTime\n" );
    write_stdout( "endTime:   $endTime\n" );
  }

  my $initCurrentHumanTime      = Time::HiRes::clock_gettime( CLOCK_REALTIME );
  my $lastEndHumanTime          = $initCurrentHumanTime + $durationInSeconds;
  my $lastFormattedEndHumanTime = format_end_human_time( $initCurrentHumanTime, $lastEndHumanTime );

  my $lastProgressLineLen = 0;


  for ( ; ; )
  {
    my $currentTime = Time::HiRes::clock_gettime( CLOCK_MONOTONIC );

    my $timeLeft = $endTime - $currentTime;

    if ( $timeLeft <= 0 )
    {
      last;
    }

    my $currentHumanTime = Time::HiRes::clock_gettime( CLOCK_REALTIME );
    my $endHumanTime     = $currentHumanTime + $timeLeft;


    # Do not change the displayed end human time if the difference is less than 1 second and we are far from it.
    # This is to prevent oscillation due to floating point inaccuracy.

    if ( $timeLeft <= 10 ||
         abs( $endHumanTime - $lastEndHumanTime ) > 1 )
    {
      if ( FALSE )
      {
        write_stdout( "\nReformatting new end human time.\n" );
      }

      $lastEndHumanTime          = $endHumanTime;
      $lastFormattedEndHumanTime = format_end_human_time( $currentHumanTime, $endHumanTime );
    }
    else
    {
      if ( FALSE )
      {
        write_stdout( "\nSkipped reformatting of new end human time.\n" );
      }
    }


    # The time left will be something like 59.9997835169997, instead of 60 seconds.
    my $roundedTimeLeft = int( $timeLeft + 0.5 );

    my $progressMsg = "Countdown: " . format_countdown_time_left( $roundedTimeLeft ) . "  ETA: $lastFormattedEndHumanTime";

    update_progress_line( $progressMsg, \$lastProgressLineLen );

    wait_for_next_round_second( $timeLeft );
  }

  return $lastProgressLineLen;
}


sub countdown_realtime ( $ $ )
{
  my $startRealTime     = shift;
  my $durationInSeconds = shift;

  my $endTime = $startRealTime + $durationInSeconds;

  if ( FALSE )
  {
    write_stdout( "startTime: $startRealTime\n" );
    write_stdout( "endTime:   $endTime\n" );
  }

  my $lastProgressLineLen = 0;

  for ( ; ; )
  {
    my $currentTime = Time::HiRes::clock_gettime( CLOCK_REALTIME );

    my $timeLeft = $endTime - $currentTime;

    if ( $timeLeft <= 0 )
    {
      last;
    }

    # The time left will be something like 59.9997835169997, instead of 60 seconds.
    my $roundedTimeLeft = int( $timeLeft + 0.5 );

    my $progressMsg = "Countdown: " . format_countdown_time_left( $roundedTimeLeft ) . "  Finish time: " . format_end_human_time( $currentTime, $endTime );

    update_progress_line( $progressMsg, \$lastProgressLineLen );

    wait_for_next_round_second( $timeLeft );
  }

  return $lastProgressLineLen;
}


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

sub main ()
{
  init_locale_info();

  my $arg_help      = 0;
  my $arg_h         = 0;
  my $arg_help_pod  = 0;
  my $arg_version   = 0;
  my $arg_license   = 0;
  my $arg_self_test = 0;
  my $arg_method;

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

  my $result = GetOptions(
                 'help'      => \$arg_help,
                 'h'         => \$arg_h,
                 'help-pod'  => \$arg_help_pod,
                 'version'   => \$arg_version,
                 'license'   => \$arg_license,
                 'self-test' => \$arg_self_test,
                 'method=s'  => \$arg_method,
               );

  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 ( $arg_self_test )
  {
    write_stdout( "Running the self-tests...\n\n" );
    self_test();
    write_stdout( "\nSelf-tests finished.\n" );
    exit EXIT_CODE_SUCCESS;
  }

  my $method = "realtime";

  if ( defined( $arg_method ) )
  {
    my $str = lc( trim_blanks( $arg_method, $whitespace ) );

    if ( $str eq "monotonic" )
    {
      $method = "monotonic";
    }
    elsif ( $str eq "real time" or
            $str eq "real-time" or
            $str eq "realtime" )
    {
      $method = "realtime";
    }
    else
    {
      die "Invalid method '$str'.\n";
    }
  }


  my $durationExpression;

  if ( scalar( @ARGV ) == 0 )
  {
    my $term = new Term::ReadLine $Script;

    # I am not fond of the default prompt underlining effect.
    $term->ornaments( 0 );

    my $prompt = "Enter the countdown duration like 5m30s (blank to exit): ";

    my $input = $term->readline( $prompt );

    if ( not defined $input )
    {
      die "\nError: End of file reached while reading from stdin.\n";
    }

    $input = trim_blanks( $input, $whitespace );

    if ( length( $input ) == 0 )
    {
      write_stdout( "Terminating because no countdown duration was specified.\n" );
      return EXIT_CODE_SUCCESS;
    }

    $durationExpression = $input;
    write_stdout( "\n" );
  }
  elsif ( scalar( @ARGV ) == 1 )
  {
    $durationExpression = trim_blanks( $ARGV[0], $whitespace );

    if ( length( $durationExpression ) == 0 )
    {
      write_stderr( "\nThe countdown duration is empty.\n" );
      return EXIT_CODE_FAILURE;
    }
  }
  else
  {
    die "Invalid number of command-line arguments. Run this tool with the --help option for usage information.\n";
  }


  # If the user interrupts the counter by mistake, he may not know anymore when it started, in order to calculate
  # how much time was left. At least that has happened to me a few times. That is the reason why
  # we are printing the start time here.
  # I have even considered writing the start time to the syslog, in case I close the whole terminal window by mistake.

  my $startRealTime = Time::HiRes::clock_gettime( CLOCK_REALTIME );

  my ( $currSec, $currMin, $currHour, $currMday, $currMon, $currYear, $currWday, $currYday, $currIsdst ) = localtime( $startRealTime );

  write_stdout( "Start time: " .
                POSIX::strftime( LONG_TIME_FMT, $currSec, $currMin, $currHour, $currMday, $currMon, $currYear, $currWday, $currYday, $currIsdst ) .
                "\n" );

  my $durationInSeconds = parse_human_duration( $durationExpression );

  write_stdout( "Countdown duration: " . format_human_friendly_duration( $durationInSeconds ) . "\n\n" );

  my $lastProgressLineLen;

  if ( $method eq "monotonic" )
  {
    $lastProgressLineLen = countdown_monotonic( $durationInSeconds );
  }
  else
  {
    $lastProgressLineLen = countdown_realtime( $startRealTime, $durationInSeconds );
  }

  update_progress_line( "Countdown timer finished.", \$lastProgressLineLen );
  write_stdout( "\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;