Do you care about the return value?
Do you need to send data to the child via its STDIN?
Do you need to collect data the child prints?
On what systems must this run?

use threads;
use threads::shared;
...
my $Bresults:shared;
async {
    $Bresults = `perl B.pl`;
}->detach;

my $Cresults = `perl C.pl`;

## Do something with the results;
[download]

Hi, thanks for useful suggestion I also need to call program D, but not untill both B and C have been executed. Please guide.

use threads;
use threads::shared;
...
my $Bresults:shared;
async {
    $Bresults = `perl B.pl`;
}->detach;

my $Cresults = `perl C.pl`;

sleep 1 until defined $Bresults;

my $Dresults = `perl D.pl $Bresults $Cresults`;
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

Take a look at fork.

After forking, we still have to wait/waitpid for the child process to end in order to avoid zombies, unless we employ the double-fork technique.

Instead, try this: system "perl B.pl &"; system "perl C.pl &"

Reference: How do I start a process in the background?

fork is a somewhat cross platform. system "... &" is rather system dependent. There is no telling what the OP is using of course and there is a fair chance that using & will do the trick for the OP.

---

Perl reduces RSI - it saves typing

To add to the comments and advice of the greatly esteemed monks, ikegami, GrandFather, and BrowserUk, and while trying not to belabor the obvious, there may not be significant speedup if either B or C takes much more time than the other, e.g., if program B takes 20 seconds to run and program C takes 1, the savings by running B and C in parallel won't exceed 1 second. See also Amdahl's Law, which describes the speedup that can be expected by running processes in parallel.