The eval command is used to execute the arguments as a shell command on unix or linux system.

Eval command comes in handy when you have a unix or linux command stored in a variable and you want to execute that command stored in the string. The eval command first evaluates the argument and then runs the command stored in the argument.

Example:

eval `ssh-agent`

eval $(ssh-agent)

An agent is a program that keeps your keys in memory so that you only need to unlock them once, instead of every time. ssh-agent does this for SSH keys. eval `ssh-agent` – this runs the agent in background, and sets the apropriate environment variables for the current shell instance.