update the SSH agent snippet

[amtoine]

i did a logout on my machine and noticed the SSH agent i took from the book stopped working 😮
i fixed it and thought it would be great to update the book 😇

description

• uses snake_case which is i think the convention with Nushell
• uses do --env to avoid leaking internal definitions to the REPL main scope
• defines the SSH agent path in a cross-platform way
• when the SSH agent file is there
  • if the process is running => load the environment and early return
  • if the process is not there, e.g. after a logout without reboot => remove the SSH agent file
• create the agent by default

[fdncred]

@amtoine i'm assuming you forgot about this PR. is it ready to land?

[amtoine]

@fdncred
aah yeah, it looks like i forgot 😮

as it looks exactly the same as the one i use everyday, i guess it's ready to land 😉

[fdncred]

lol. Thanks!

[wanesty]

@amtoine i'm assuming you wrote $env.USER? | default $env.USERNAME for cross-platform compatibility but $env.USERNAME doesn't exists on linux, so i think both $env user variables would need a ? and thus maybe a check