Execute ProxyCommand in a shell

[joshheinrichs-shopify]

The ProxyCommand in my ssh config looks something like

ProxyCommand foo --bar\=baz

The backslash ahead of = is definitely weird, but the ssh config gets generated by a Ruby script, and that's how Ruby's Shellwords.escape escapes tokens. This config works with ssh, but not open-remote-ssh because the backslash ends up in the argument passed to foo.

According to man ssh_config, "[ProxyCommand] is executed using the user's shell 'exec' directive to avoid a lingering shell process," so I guess ssh just substitutes the tokens in the string and executes the command in a shell, and the shell processes the backslash.

We can see that ssh doesn't try escaping tokens by running

$ ssh -o ProxyCommand='printf "%%q\n" %h 1>&2' "foo bar"
foo
bar

Despite "foo bar" being one token, it gets passsed to printf as two arguments, so I guess if we want to match ssh's behaviour we should do the same? I'm not sure what's up with Windows, so I left it alone for now.

[joshheinrichs-shopify]

Ideally the ssh config parsing library wouldn't attempt to split ProxyCommand since it strips quotes that could theoretically matter for environment variables. If we changed that in your fork (maybe as a parser option so we can contribute it back?), it looks like we might be able to have the same handling across windows and unix?