Popen getting pid of newly run process

Question

I want to run some application in background and later kill it by pid.

pipe = IO.popen(\"firefox \'some_url\' 2>&1 &\")
pipe.pid

Answer 1

Since you are running it in the background (command &), you get the interpreter's PID:

>> pipe = IO.popen("xcalc &")
>> pipe.pid 
=> 11204

$ ps awx | grep "pts/8"
11204 pts/8    Z+     0:00 [sh] 
11205 pts/8    S+     0:00 xcalc

Drop the &:

>> pipe = IO.popen("xcalc")
>> pipe.pid
=> 11206

$ ps awx | grep "pts/8"
11206 pts/8    S      0:00 xcalc

For the additional issue with the redirection, see @kares' answer