Set a default keypair via USER_KEY and USER_PUKBEY variables.
Usage
my_key()
my_pubkey()
Arguments
Details
The my_key() function checks environment variable USER_KEY for a
path to a private keyfile. If unset it defaults to "~/.ssh/id_rsa".
The my_pubkey() function first tries USER_PUBKEY and if unset
it checks for USER_KEY to derive the corresponding pubkey. If both are
unset it defaults to "~/.ssh/id_rsa.pub".