Listing 2. Perl Script

#
# ws.pl -- Take data and HTML template and produce
#          an output HTML file.
#

$TEMPLATE='/home/weather/WWW/wsTemplate.html';

$twentyfourhours = 86400;  #seconds in a day

# Filename for today's data
$DATADIR="/home/weather/data";
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
	localtime(time);
$TODAY= sprintf "%02d%02d%02d", $mon+1, $mday, $year;
$DATAFILE="$DATADIR/$TODAY";

# Calculate yesterday's filename
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
	localtime(time-$twentyfourhours);
$YESTERDAY= sprintf "%02d%02d%02d", $mon+1, $mday, $year;
$MYESTERDAYFILE="$DATADIR/$YESTERDAY.max";
$mYESTERDAYFILE="$DATADIR/$YESTERDAY.min";

$CBP_CORRECTION = 6.68;  # Correction for atmospheric pressure 
			 # derived with help from local weather expert

# Match these patterns in the template file.
# Fill in the appropriate information
#  from the latest data record.
# %TIME% %DATE%
# %FTEMP%  (Farenheit) %CTEMP% (Celcius) %HUMIDITY%
# %BP% %CBP% (pressure and corrected pressure)
# %WSPEED% %KWSPEED% %WDIRECTION%  (speed in MPH and KPH)
# %RAIN%
# YM - yesterday Max, Ym - yesterday Min
# %YMTEMP% %YmTEMP% %YMHUMIDITY% %YmHUMIDITY%
# %YRAIN%

if( -r $DATAFILE)
{
	$lastline = `tail -1 $DATAFILE`;
}
else
{
	die "No current datafile $DATAFILE";
}

($time, $date, $wdir, $wspeed, $aux, $intemp, $outtemp, $hum, $bp,
 $raind, $rainm, $rain_rate) = split(' ',$lastline);

# Get stuff from yesterday's Max file
if( -r $MYESTERDAYFILE)
{
	$maxline = `tail -1 $MYESTERDAYFILE`;
}
($Max, $Mdate, $Mwdir, $Mwspeed, $Maux, $Mintemp, $Mouttemp, $Mhum, $Mbp,
 $Mraind, $Mrainm, $Mrain_rate) = split(' ',$maxline);

# Get stuff from yesterday's Min file
if( -r $mYESTERDAYFILE)
{
	$minline = `tail -1 $mYESTERDAYFILE`;
}
($max, $mdate, $mwdir, $mwspeed, $maux, $mintemp, $mouttemp, $mhum, $mbp,
 $mraind, $mrainm, $mrain_rate) = split(' ',$minline);


# I do some messaging of the data to remove some indicators
#  and expand others.
$wspeed =~ s/MPH//;
$wdir =~ s/E/east /g;
$wdir =~ s/N/north /g;
$wdir =~ s/W/west /g;
$wdir =~ s/S/south /g;
$outtemp =~ s/F//;
$outtemp =~ s/^0//;
$Mouttemp =~ s/F//;
$Mouttemp =~ s/^0//;
$mouttemp =~ s/F//;
$mouttemp =~ s/^0//;
$intemp =~ s/F//;
$intemp =~ s/^0//;
$hum =~ s/%//;
$hum =~ s/^0//;
$mhum =~ s/%//;
$mhum =~ s/^0//;
$Mhum =~ s/%//;
$Mhum =~ s/^0//;
$bpdir = "rising" if ($bp =~ /R/);
$bpdir = "steady" if ($bp =~ /S/);
$bpdir = "falling" if ($bp =~ /F/);
$bp =~ s/[A-Z]//;
$raind =~ s/\"D//;
$Mraind =~ s/\"D//;
$rainm =~ s/\"M//;
$rain_rate =~ s/\"R//;

$outctemp = sprintf("%3.1f",ftoc($outtemp));
$dewpoint = sprintf("%3.0f",dewpoint($outtemp,$hum));

$cbp = &cbp($bp);

$kwspeed = sprintf("%2.0f", $wspeed * 1.609);

open(T,"$TEMPLATE") or die "no such file $TEMPLATE\n";

while ()
{
	# For each line in the template file...
	# Do the actual template replacements
	s/%TIME%/$time/;
	s/%DATE%/$date/;
	s/%FTEMP%/$outtemp/;
	s/%CTEMP%/$outctemp/;
	s/%HUMIDITY%/$hum/;
	s/%DEWPOINT%/$dewpoint/;
	s/%CBP%/$cbp $bpdir /;
	s/%BP%/$bp/;
	s/%WSPEED%/$wspeed/;
	s/%KWSPEED%/$kwspeed/;
	s/%WDIRECTION%/$wdir/;
	s/%RAIN%/$raind/;
	s/%YMHUMIDITY%/$Mhum/;
	s/%YmHUMIDITY%/$mhum/;
	s/%YMTEMP%/$Mouttemp/;
	s/%YmTEMP%/$mouttemp/;
	s/%YRAIN%/$Mraind/;

	# Print this doctored-up line.
	print $_;
}

# Subroutine for correction of atmospheric pressure
sub cbp
{
	local($in) = @_;
	return(sprintf("%2.2f", $in + $CBP_CORRECTION));
}

# Subroutines for F-->C  and C-->F temp conversions
sub ctof
{
	local ($C) = @_;
	$F = (9/5 * $C) + 32;
	return $F;
}

sub ftoc
{
	local ($F) = @_;
	$C = 5/9 * ($F - 32);
	return $C;
}

# Subroutine to calculate dewpoint
sub dewpoint
{
	local ($F, $H) = @_;

	$rh = $H/100; # RH. Fraction, [0..1] not %.
	$t = ftoc($F); #Celsius Temperature

	$es = 6.112 * exp(17.67 * $t / ($t + 243.5));
	$e = $rh * $es;
	$loge = log($e/6.112);
	$dp = 243.5 * $loge/(17.67 - $loge);
        return ctof($dp);
}