Linux – What’s the difference between BSD-style and Unix-style command line options

The commands dig and host should be what you're looking for ;)

On *nix systems, you can use this command:

dig -x [address]

Alternatively, you can add +short at the end of the dig command to output only the DNS result.

There's also nslookup on both *nix and Windows systems for reverse DNS requests.

In your login shell's profile files you can set up some things that you will use during your session, and which only need to be done once. Some ideas:

• create a temporary file containing the IP address you connected from, later on you can include it in some scripts setting firewall rules.
• run ssh-agent, ask for your SSH keys, and store the SSH agent environment variables in a file.
• if that is a limited machine, and your co-workers want to be aware of each others logins, write(1) messages informing them of your login.

In a non-login shell's files (.bashrc) you should configure your shell:

• Fancy prompt
• set aliases
• set history options
• define custom shell functions
• export environment variables, (maybe PAGER, EDITOR if system-wide settings suck)
• load ssh-agent variables saved in .bash_profile

Usually, you would include .bashrc from .bash_profile with the following. Then login shell gets all your customizations, and .bash_profile file does not have to duplicate things that are already in .bashrc.

[[ -f ~/.bashrc ]] && . ~/.bashrc