How does dmenu_run work?

My system is

9.4

which uses

kernel 4.9.0-8-amd64

and

$SHELL

on my system gives

/bin/bash

and

/bin/sh

is a link to

/bin/dash

. I was curious why every time I run an application with

from

there is an additional

/bin/bash

process that runs as the parent, so I dug further into the script of

: #!/bin/sh dmenu_path | dmenu "$@" | ${SHELL:-"/bin/sh"} & I can't understand why my computer has

/bin/bash

instead of

/bin/sh

. I also read the correspond source code in

. It shows that it just simply

and

. There is no reason for

/bin/bash

to run instead of

/bin/sh

.