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# cron -- perl implementation of cron for NT/95
###############################################################################
#
# by Scott McMahan
# version 1.0 beta prerelease
#
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# Usage: cron <crontab file>
#
# Where <crontab file> is a valid crontab file in the usual UNIX format.
# Defaults to file named "crontab" in current directory
###############################################################################
# There are some configuration options after the comments.
# They're probably okay as-is, but may be worth looking at.
###############################################################################

###############################################################################
# Author's Notes:
# Perl is obviously a prerequisite for using this program!
# I chose perl because it was trivial to implement the file parser.
# Just fire this up when you log in, and it'll keep running.
# Warning: this is not a complete implementation of cron!
# It's just the features I needed for my own task automation. It's about
# 86% authentic, when you discount the differences in starting it and 
# security between UNIX and NT.
# I do not support:
#  - ranges in entries (3,4,5,6 is okay, 3-6 is not)
#  - Daylight savings time (schedule stuff some other time besides 
#    the overlap hour, or implement the logic and send me a copy!) 
#  - embedded newlines in commands (run multiple commands from
#    a script and run the script from cron)
#  - usage is different (on the command line, a crontab file is
#    specified or the default "crontab" in the current directory
#    is opened)
#  - no security or allow/deny stuff (this cron assumes you're
#    running from a single logged-on NT account)
#
# Wish list:
#  [ ] Support for ranges would be nice
#  [ ] DST logic
#  [ ] In-crontab "pragmas" or command line switches for log file 
#      and logging level
#  [ ] Leading 0 logic for date/times -- I wrote this once and will
#      have to find it
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###############################################################################
# If you're not familiar with crontab files, they have lines 
# with the following:
#
# min hour monthday month weekday command
#
#  - Lines beginning with '#' are comments and are ignored.
#  - The numeric entries can be separated by commas -- eg 1,2,3
#  - Ranges for each are as follows:
#           minute (0-59),
#           hour (0-23),
#           day of the month (1-31),
#           month of the year (1-12),
#           day of the week (0-6 with 0=Sunday).
###############################################################################

###############################################################################
# configuration section
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# Note there are two levels of logging: normal logging, controlled by 
# the logfile variable, logs all commands executed and when they're
# executed. The message facility prints messages about everything that
# the program does, and is sent to the screen unless the msgfile 
# variable is set. Use the msgfile only in emergencies, as voluminous
# output is generated (so much so that leaving msgfile active all night
# could exhaust available disk space on all but the most capacious
# systems) -- its primary purpose is for emergency debugging.
# Due to the peculiar construction of the log functions, the log and
# msg files can be the same file. This may or may not be good.

$logfile = "cronlog.txt";
$msgfile = ""; # assign this only in emergency

# end of configuration

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# in_csl searches for an element in a comma separated list
###############################################################################

sub in_csl {
    ($what, $csl) = @_;
    MSG("Processing CSL");
    @a = split(/,/, $csl);
    for $x (@a) {
	MSG("is $what equal to item $x?");
	if ($what eq $x) {
	    return 1;
	}
    }
    return 0;
}

###############################################################################
# main program
###############################################################################

if (defined $ARGV[0]) {
    ACT("using $ARGV[0] as crontab file\n");
    $crontab = $ARGV[0];
}
else {
    ACT("using default file crontab\n");
    $crontab = "crontab";
}

while (1) {

    open(F, "$crontab") or die "Can't open crontab; file $crontab: $!\n";
    $line = 0;

    while (<F>) {
   	$line++;
	
   	if (/^$/) {
	    MSG("blank line $line");
	    next;
   	}

   	if (/^#/) {
	    MSG("comment on line $line");
	    next;
   	}

   	# mon = 0..11 and wday = 0..6
   	($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = 
	    localtime(time);
   	$mon++; # to get it to agree with the cron syntax

   	($tmin, $thour, $tmday, $tmon, $twday, $tcommand) = split(/ +/, $_, 6);
	
   	MSG("it is now $hour:$min:$sec on $mon/$mday/$year wday=$wday");
   	MSG("should we do $thour:$tmin on $tmon/$tmday/--, wday=$twday?");
	
   	$do_it = 0; # assume don't do it until proven otherwise
	
   	# do it -- this month?
   	if ( ($tmon eq "*") || ($mon == $tmon) || &in_csl($mon, $tmon)) {
	    $do_it = 1;
	    MSG("the month is valid");
   	}
   	else {
	    $do_it = 0;
	    MSG("cron: the month is invalid");
   	}
	
   	# do it -- this day of the month?
   	if ( $do_it && ( ($tmday eq "*") 
			|| ($mday == $tmday) || &in_csl($mday, $tmday)) ) {
	    $do_it = 1;
	    MSG("the day of month is valid");
   	}
   	else {
	    $do_it = 0;
	    MSG("the day of month is invalid");
   	}
	
   	# do it -- this day of the week?
   	if ( $do_it && ( ($twday eq "*") 
			|| ($wday == $twday) || &in_csl($wday, $twday)) ) {
	    $do_it = 1;
	    MSG("the day of week is valid");
   	}
   	else {
	    $do_it = 0;
	    MSG("the day of week is invalid");
   	}
	
   	# do it -- this hour?
   	if ( $do_it && ( ($thour eq "*") || 
			($hour == $thour)|| &in_csl($hour, $thour) ) ) {
	    $do_it = 1;
	    MSG("the hour is valid");
   	}
   	else {
	    $do_it = 0;
	    MSG("the hour is invalid");
   	}
	
   	# do it -- this minute?
   	if ( $do_it && ( ($tmin eq "*") || 
			($min == $tmin) || &in_csl($min, $tmin) ) ) {
	    $do_it = 1;
	    MSG("the min is valid");
   	}
   	else {
	    $do_it = 0;
	    MSG("the minute is invalid");
   	}
	
   	if ($do_it) {
	    chop $tcommand;
	    ACT("executing command <$tcommand>");
	    system ("start $tcommand");
   	}
    }
    
    close(F);
    MSG("***-----***");
    sleep(60);
}

exit;


###############################################################################
# Log activity
###############################################################################

sub ACT {
    # mon = 0..11 and wday = 0..6
    ($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = 
	localtime(time);
    $mon++; # to get it to agree with the cron syntax

    print "cron [$mon/$mday/$year $hour:$min]: @_\n";
    
    # since we're appending the log, always open it only as little
    # as necessary, so if we crash the info will be there
    open(LOGFILE, ">>$logfile") or return;
    print LOGFILE "cron [$mon/$mday/$year $hour:$min]: @_\n";
    close(LOGFILE);
}

###############################################################################
# routine to log messages
# logs to screen unless $msgfile is set to a filename
###############################################################################

sub MSG {
    # mon = 0..11 and wday = 0..6
    ($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = 
	localtime(time);
    $mon++; # to get it to agree with the cron syntax

    print "cron*[$mon/$mday/$year $hour:$min]: @_\n";    

    return unless $msgfile;

    # since we're appending the log, always open it only as little
    # as necessary, so if we crash the info will be there
    open(LOGFILE, ">>$logfile") or return;
    print LOGFILE "cron*[$mon/$mday/$year $hour:$min]: @_\n";    
    close(LOGFILE);

}