ssh Bad local forwarding specification when passing port as parameter

[int]$port:localhost:[int]$port

You cannot use casts this way, and they're also not necessary, given that you can only ever pass strings as arguments to external programs (aside from that, $port already is of type [int]).

Instead, use an (implicit) expandable string to compose your argument:

ssh -fNL ${port}:localhost:${port}

• ${port}:localhost:${port} is implicitly treated as if it were enclosed in "...", i.e. as an expandable (interpolating) string .

  • In other words: "${port}:localhost:${port}" works too, and you may prefer it for conceptual clarity and to avoid cases where unquoted arguments aren't implicitly treated as expandable strings.

    • E.g., Write-Output "$baseName.txt" appends literal .txt to the value of $baseName, whereas Write-Output $baseName.txt tries to access a (nonexistent) .txt property on the object stored in $baseName; see this answer for background information.

• Note the need to enclose the variable name, port, in {...} so as to delimit it; without it, the : would be considered part of the variable reference, making $port the a scope or namespace prefix of the following variable reference, which expands to the empty string due to non-existence: $port:localhost.

  • This delimiting isn't strictly necessary in the second ${port} reference, but was chosen for symmetry here.
  • See this answer for background information.