• Pascal

var
  p: tprocess;
begin
  p.Executable := 'program_x';
  p.Parameters.Add('a');
  p.Parameters.Add('b');
  p.Execute;
end.

• C

int system("x a b");

• C#

string[] args = { "a", "b"};
Process.Start(x, string.Join(" ", args));

• D

spawnProcess([x, "a", "b"]);

• Fortran

program p
   integer :: i

   call execute_command_line("x a b", exitstat=i)
   print *, "Exit status of x was ", i

   call execute_command_line("x a b", wait=.false.)
   print *, "running x in the background"
end program p 

• Go

err := exec.Command("x", "a", "b").Run()

• Haskell

spawnProcess x ["a","b"]

• JS

exec(`${x} a b`);

• Java

Runtime.getRuntime().exec(new String[]{"x", "a", "b"});

• Java

var b = new ProcessBuilder(of("x", "a", "b"));
try {
    b.start().waitFor();
} catch (Exception e) {
    throw new RuntimeException(e);
}

• Lisp

(sb-ext:run-program '("a" "b") "/path/to/x")

• Lua

os.execute(x .. 'a b')

• PHP

exec($x . " a b");

• Perl

system $x, 'a', 'b';

• Python

subprocess.call(['x', 'a', 'b'])

• Ruby

`x a b`

• Rust

let output = Command::new("x")
    .args(&["a", "b"])
    .spawn()
    .expect("failed to execute process");

• Rust

let output = Command::new("x")
        .args(&["a", "b"])
        .output()
        .expect("failed to execute process");

• Rust

let output = Command::new("x")
        .args(&["a", "b"])
        .status()
        .expect("failed to execute process");