Count Entries in hash and how frequent they change - linux

Question

I have a script that reads CAN bus signals and displays them to screen but I need to add a signal counter and frequency.
So I need to count how many times has this $id appeared so far and how many milliseconds ago did was it added to the hash table.
#!/usr/bin/perl -w
use strict;
open my $can_bus, "./receivetest |"
or die "Couldn't read from CAN bus: $!";
my %last_value;
while (<$can_bus>) {
if( /^(........:...) (........) (.*)$/ )
{
my ($something, $id, $payload) = ($1,$2,$3);
$last_value{ $id } = $payload;
system('clear'); #clear screen
#Print Table
for my $id (sort keys %last_value) {
print "$id\t $last_value{ $id }\n";
}
}
else {
warn "ignore unknown line: ";
warn $_;
}
}
This is my code so far.

Answer 1

You can store different values for one $id key if you expand your hash by adding more keys after the $id key. For example:
if (defined $last_value{ $id } ){
$last_value{ $id }{COUNT} += 1;
my $time_diff = $now_milli - $last_value{ $id }{TIME};
$last_value{ $id }{TIME} = $now_milli;
$last_value{ $id }{DIFF} = $time_diff;
$last_value{ $id }{PAYLOAD} = $payload;
}else{
$last_value{ $id }{TIME} = $now_milli;
$last_value{ $id }{DIFF} = "NA";
$last_value{ $id }{COUNT} = 1;
$last_value{ $id }{PAYLOAD} = $payload;
}
To get current time in milliseconds you can use Time::HiRes qw/gettimeofday/ which is a part of Perl core:
use Time::HiRes qw/gettimeofday/;
my $now_milli = 1000 * gettimeofday();
Finally, to print information stored in the %last_value hash:
foreach my $id (keys %last_value){
print "ID: ", $id, "\n";
print "Count: ", $last_value{$id}{COUNT}, "\n";
print "Time from last: ", $last_value{$id}{DIFF}, "\n";
print "Payload: ", $last_value{$id}{PAYLOAD}, "\n";
}