Why does this Powershell subexpression operator command not work?

Question

I am trying to understand why a Powershell one liner I want to use to setup a port proxy to a WSL instance seemingly does not work, but running it without the grouping/substitution does work. Steps:

Get the IP address of WSL instance:

wsl hostname -I

> 172.18.108.185

Try one liner with the previous command as subexpression:

netsh interface portproxy add v4tov4 listenport=3443 `
listenaddress=0.0.0.0 connectport=3443 `
connectaddress=$(wsl hostname -I)

That seems to work because listing port proxies shows it:

netsh interface portproxy show v4tov4

> Listen on ipv4:             Connect to ipv4:
> 
> Address         Port        Address         Port
> --------------- ----------  --------------- ----------
> 0.0.0.0         3443        172.18.108.185  3443

(I have also tried it without the $.)

However, the proxy forwarding does not actually work.

If I then do the same command without the substitution:

netsh interface portproxy add v4tov4 listenport=3443 `
listenaddress=0.0.0.0 connectport=3443 `
connectaddress=172.18.108.185

The output looks exactly the same:

netsh interface portproxy show v4tov4

> Listen on ipv4:             Connect to ipv4:
> 
> Address         Port        Address         Port
> --------------- ----------  --------------- ----------
> 0.0.0.0         3443        172.18.108.185  3443

However, this time it works.

What is different between these two executions such that one works, one doesn't, and yet the results look exactly the same?

Answer 1

Abraham Zinala provided the crucial pointer:

The output from wsl hostname -I - surprisingly - has a trailing space, which must be trimmed in order for the IP address represented by the output to be used as an argument passed to netsh:

netsh interface portproxy add v4tov4 listenport=3443 `
  listenaddress=0.0.0.0 connectport=3443 `
  connectaddress=$((wsl hostname -I).Trim())