When I do bash scripts I would usually just use && to chain processes that depend on the one before.
I connect my network to an open wireless AP with this simple one liner from bash: 
root@ obarun ~ # ip link set [interface] up && iw dev [interface] connect [SSID] && dhcpcd -b [interface]
How would I make a frontend exec statement out of this? I have tried this before and the chaining doesn't work as expected. I don't want to set up three separate services though. I would like to have a "wireless" service and have that enabled on boot.
[main]
@ type = classic
@ name = wifi
@ description = "bring wireless interface up and connect to open home network"
@ user = ( root )

[start]
@ build = auto
@ execute = ( ip link set wlp4s0 up && iw dev wlp4s0 connect openhome && dhcpcd -b wlp4s0 )
Should I use bash for shebang instead? 
@ build = custom
@ shebang = "/usr/bin/bash"
@ execute = (
    exec 2>&1
    ip link set wlp4s0 up &&
    iw dev wlp4s0 connect openhome &&
    dhcpcd -b wlp4s0
)
when you pick 'auto' at @ build key you ask for execline syntax and so '&&' do not exist on execline scripts
So you can do something like this: 
@ execute=(
if { ip link set wlp4s0 up }
if { iw dev wlp4s0 connect openhome }
dhcpcd -b wlp4s0
)
Also your second proposition should works :).Like you saw, you can use any language that you want, just set the proper interpreter like you did.

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