On 2022-06-10 at 11:25, rhkramer@gmail.com wrote: > In my (seemingly unending) quest to understand ssh, I've come across a > document that calls for running =eval 'ssh-agent'= from a command line. Note that here you have 'ssh-agent', with single-quotes AKA apostrophes... > I wondered why, as I thought I would get the same result from just running > =ssh-agent=, but the results are different -- see below: > > $ eval `ssh-agent` ...but here you have `ssh-agent`, with backticks. Backticks are an older syntax for "run this command in a subshell, and put the output of that command in this place on the command line, before running the rest of this command". The newer syntax for the same thing is $(). > Agent pid 23929 > > $ ssh-agent > SSH_AUTH_SOCK=/tmp/ssh-uLqQ9VWX0RL7/agent.23932; export SSH_AUTH_SOCK; > SSH_AGENT_PID=23933; export SSH_AGENT_PID; > echo Agent pid 23933; > > Can anybody on here explain what is going on / why? Because of the subshell effect, what this effectively does is run the commands that got printed by running ssh-agent, as Loïc Grenié already indicated. (There's also considerations involving the semicolons and the fact that eval explicitly combines its arguments into one string before treating them as commands to be run by the shell, but I don't have my head fully around those yet, so I'm not going to try to explain them. It seems to produce intuitive and useful behavior, in any case.) -- The Wanderer The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. -- George Bernard Shaw
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