Perl error handling - perl

Question

how can i cache errors in perl? Is there try/cache like in JS? I would like if any error occurs to go to the start of the script.
And if anyone has an idea of improvement for the script below let me know because this is my first one in perl. The script just has to loop forever and never stop. :)
#!/usr/bin/perl
use strict;
use warnings;
use LWP::UserAgent;
use JSON;
use HTTP::Request::Common qw(POST GET);
use Encode qw(encode);
use DBI;
use Time::Piece;
# Beware: we disable the SSL certificate check for this script.
$ENV{PERL_LWP_SSL_VERIFY_HOSTNAME}=0;
# Debugging: off=0, medium=3, extensive=5
my $debuglevel=0;
my ($host,$username,$password)=('192.168.xxx.xxx','xxxx','xxxx');
# Define cms api key and nodeid.
my ($cmsapi,$cmsnode)=('xxxxxxxxx','1');
# Define all parameters to be logged each script's iteration.
# #parameterlist[x][$parameterid,$parameterlongtext,$parametershorttext,$data]
# which corresponds for FHEM's DbLog with:
# #parameterlist[x][$parameterid,$parameterlongtext,READING ,VALUE]
# $parameterlist[x][3] will be populated by the script, thus here undefined in each line (the last value is missing).
my #parameterlist=(
[3922,"Status TC","statusHeatPump"],
[3931,"Zunanja temperatura","outsideTemperature"],
[3924,"Status zalogovnika","statusBuffer"],
[3925,"Status bojlerja","statusBoiler"],
[3940,"Temperatura bojlerja","boilerTemperature"],
[3943,"Temperatura zalogovnika","bufferTemperature"],
[4331,"Temperatura nadstropja","floorTemperature"],
[3811,"Temperatura pritličja","groundTemperature"],
);
# We substitute the text for the burner's status with an integer, so plots are easier.
# Define which parameter holds the burner's status.
my $parameterstatusHeatPump=3922;
my #statusHeatPumpmatrix=(
["Off",0],
["Heating mode",50],
);
sub trim() {
my $str = $_[0];
$str =~ s/^\s+|\s+$//g;
return $str;
};
print "DEBUG: *** Script starting ***\n" if($debuglevel>0);
while (1) {
sleep 1;
my $ua=LWP::UserAgent->new;
my $request=HTTP::Request->new(GET=>'https://'.$host.'/api/auth/login.json?user='.$username.'&pwd='.$password);
my $response=$ua->request($request);
my $decoded=decode_json($response->decoded_content( charset => 'none'));
my $success=$decoded->{'Result'}{'Success'};
my $sessionid=$decoded->{'SessionId'};
print "DEBUG: ".$response->content."\n" if($debuglevel>4);
print "DEBUG: ".$success."\n" if($debuglevel>4);
my $i=0;
my $j=0;
my $parameterid;
my $dataValue;
my $rightnow;
my $data = "empty";
while (defined($parameterlist[$i][0])) {
$parameterid=$parameterlist[$i][0];
$request=HTTP::Request->new(GET=>'https://'.$host.'/api/menutree/read_datapoint.json?SessionId='.$sessionid.'&Id='.$parameterid);
$response=$ua->request($request);
$decoded=JSON->new->utf8->decode($response->decoded_content( charset => 'none'));
$success=$decoded->{'Result'}{'Success'};
$dataValue=encode('UTF-8', $decoded->{'Data'}{'Value'});
$parameterlist[$i][3]=&trim($dataValue);
if ($parameterlist[$i][0]==$parameterstatusHeatPump) {
$j=0;
while (defined($statusHeatPumpmatrix[$j][0])) {
if ($statusHeatPumpmatrix[$j][0] eq $parameterlist[$i][3]) {
$parameterlist[$i][3]=$statusHeatPumpmatrix[$j][1];
print "DEBUG: Substituting text of HeatPump\n" if($debuglevel>0);
};
$j++;
}
}
print "DEBUG: ".$response->content."\n" if($debuglevel>4);
print "DEBUG: ".$success."\n" if($debuglevel>4);
print "DEBUG: ".$parameterlist[$i][1]."=".$dataValue."\n" if($debuglevel>0);
$rightnow=localtime->strftime('%Y-%m-%d %H:%M:%S');
if ($data eq "empty"){
$data = $parameterlist[$i][2].':'.$parameterlist[$i][3];
}
else{
$data = $parameterlist[$i][2].':'.$parameterlist[$i][3].','.$data;
}
$i++;
}
print "JSON data = ".$data."\n" if($debuglevel>0);;
#Post data
my $req=HTTP::Request->new(POST=>'http://cms.org/input/post.json?apikey='.$cmsapi.'&node='.$cmsnode.'&json={'.$data.'}');
my $resp = $ua->request($req);
if ($resp->is_success) {
my $message = $resp->decoded_content;
print "Received reply: $message\n" if($debuglevel>0);
}
else {
print "HTTP POST error code: ", $resp->code, "\n" if($debuglevel>0);
print "HTTP POST error message: ", $resp->message, "\n" if($debuglevel>0);
}
}
print "DEBUG: *** Script ended ***\n\n" if($debuglevel>0);

Answer 1

I am answering the specific:
Is there try/cache like in JS?
Yes there is. Instead of
try {
possible evil code;
} catch (e) {
...
}
in perl you write
eval {
possible evil code;
};
if ($#) {
...
}
where $# is the message with which youre code died. BTW - don't vorget the ';' after the eval code.
HTH
Georg

Answer 2

In Perl you can use eval,
For Perl Script:
eval {
your code statement;
}
if($#){
print qq{Error: $#};
}
For CGI file use like below if you want to print the error:
eval {
your code statement || die "Error: $!";
}
if($#){
print qq{Error: $#};
}