Hold private keys used for public key authentication. ssh-agent is usually executed at the beginning of an X or login session; then all other windows or programs given as command are run as clients of ssh-agent. When a command is specified, the command and any arguments are executed. The agent dies when the command completes. Use ssh-add to add keys to the agent. Operations that require a private key are performed by the agent, which returns the results to the requestor.
Bind the agent to the socket bind_addr (default is /tmp/ssh-nnnnnnnn/agent, where nnnnnnnn is a generated number).
Write csh commands to standard output. This is the default if the environment variable SHELL looks like a csh-type shell.
Kill the current agent.
Write Bourne shell commands to standard output. This is the default if the environment variable SHELL does not look like a csh-type command.