1

What am I not understanding?

I run ssh-agent and it appears to set some environment variables but when I echo them, I don't get back what I expect.

❯ ssh-agent
SSH_AUTH_SOCK=/var/folders/pn/b_2jl_j55kl504pvctj2jw2c0000gn/T//ssh-SGC2u3LSE0Gu/agent.6521; export SSH_AUTH_SOCK;
SSH_AGENT_PID=6522; export SSH_AGENT_PID;
echo Agent pid 6522;

~
❯ echo $SSH_AGENT_PID


~
❯ echo $SSH_AUTH_SOCK
/private/tmp/com.apple.launchd.lfH6wkqh4H/Listeners
skube
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    Note despite the fact you did not manage to set the variables, the process with PID 6522 is running and listening on the socket. You may want to kill it manually. – Kamil Maciorowski Aug 01 '22 at 17:05

1 Answers1

4

ssh-agent is a separate executable. It can neither set nor change variables and the environment of your shell. Without a debugger, only the shell itself can do this (compare this answer).

Therefore ssh-agent generates shell code for a shell to evaluate. You actually saw the code printed to your console, but not evaluated. The right way to start a new ssh-agent and set variables is:

eval "$(ssh-agent)"

Notes:

  • Manuals and how-tos usually use

     eval `ssh-agent`

    because it's a universal syntax that should work in many shells, no matter if sh-like or csh-like. The command with "$(…)" follows modern good practices in sh-like shells and your zsh is sh-like in this context.

  • ssh-agent tries to tell if your shell is sh-like or csh-like, and generates shell code accordingly. In other words it behaves like ssh-agent -s or ssh-agent -c, depending on what it "thinks" about your shell. If you know your shell is zsh then you may prefer eval "$(ssh-agent -s)" in case the tool guesses wrong for some reason. Usually this is not needed though.

  • Almost always you should avoid eval, in general it's hard to use it safely, some say "eval is evil". With ssh-agent it's OK though, because ssh-agent is deliberately designed to be used with eval, it generates fully controlled shell code that stays away from areas and pitfalls that make eval "evil".

Kamil Maciorowski
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