Refactored chained elsif (with regex) to send the table to Perl. But how does my code work?

I had a long if elsif coded block like this where I grab the output of a command using Capture :: Tiny and then extract it using a series of regexps.

sub capture_cpu_test {
    my ($cmd) = @_;
    print '--------------------', "\n";
    print 'COMMAND is: ', "$cmd", "\n";

    #capture an output of sysbench command
    my ( $stdout_to_format, $stderr, $exit ) = capture {
        system($cmd );
    };

    #split on newline to separately analyze later
    my @output_lines = split( "\n", $stdout_to_format );

    #set hash to collect param => param_value pairs
    my %plotting_hash = ();

    foreach my $line (@output_lines) {
        if ( $line =~ m/\ANumber\s+of\s+threads:\s+(\d+)\z/xms ) {
            $plotting_hash{num_threads}   = $1;
        }

        #long list of elseif continues

        elsif ( $line =~ m{\A\s+events\s+\(avg\/stddev\):\s+(.+?)\/(.+?)\z}xms ) {
            $plotting_hash{events_avg}    = $1;
            $plotting_hash{events_stddev} = $2;
        }
    }

    #returns ref to plotting_hash to combine upstream
    my $hash_plot_ref = \%plotting_hash;
    print 'Printing $hash_plot_ref inside capture_cpu_test: ', "\n";
    print Dumper($hash_plot_ref);
    return $hash_plot_ref;
}

      

        
        
        
      

    

I wanted to make it more readable, so I changed this elsif block to mailing table using the answers on the net and no problem, it works:

#set dispatch table with regex => sub {} pairs
my %plotting_hash  = ();
my %dispatch_regex = (
    qr/\ANumber\s+of\s+threads:\s+(\d+)\z/xms => 
      sub { $plotting_hash{num_threads}   = $1 },

    #more entries here

    qr{\A\s+events\s+\(avg\/stddev\):\s+(.+?)\/(.+?)\z}xms =>
      sub { $plotting_hash{events_avg}    = $1;
            $plotting_hash{events_stddev} = $2; },
);

#populate the %plotting_hash by calling dispatch table (%dispatch_regex)
my $code_ref;
foreach my $line (@output_lines) {
    foreach my $regex ( keys %dispatch_regex ) {
        if ( $line =~ $regex ) {
            $code_ref = $dispatch_regex{$regex};
            $code_ref->();
            last;
        }
    }
}

      

        
        
        
      

    

I get something like this:

$hash_plot_ref = {
      'num_threads'         => '4',
      'events_stddev'       => '50.98',
      'events_avg'          => '2500.0000',
      ...
};

      

        
        
        
      

    

• I would like to know how this dispatch works from a regex in a data string to an anonymous subroutine. How are the ($ 1, $ 2) captures passed to anon sub? How exactly do these advertisements get parameters? I tried to figure it out with B :: Deparse, but that says little.
• How can I write it more readable? I've tried with tabbed tees and for / when (not shown here) and it still doesn't look much better than the elseif chain.