What are the functional differences between .profile .bash_profile and .bashrc
Solution 1:
.bash_profile and .bashrc are specific to bash, whereas .profile is read by many shells in the absence of their own shell-specific config files. (.profile was used by the original Bourne shell.) .bash_profile or .profile is read by login shells, along with .bashrc; subshells read only .bashrc. (Between job control and modern windowing systems, .bashrc by itself doesn't get used much. If you use screen or tmux, screens/windows usually run subshells instead of login shells.)
The idea behind this was that one-time setup was done by .profile (or shell-specific version thereof), and per-shell stuff by .bashrc. For example, you generally only want to load environment variables once per session instead of getting them whacked any time you launch a subshell within a session, whereas you always want your aliases (which aren't propagated automatically like environment variables are).
Other notable shell config files:
/etc/bash_profile (fallback /etc/profile) is read before the user's .profile for system-wide configuration, and likewise /etc/bashrc in subshells (no fallback for this one). Many systems including Ubuntu also use an /etc/profile.d directory containing shell scriptlets, which are . (source)-ed from /etc/profile; the fragments here are per-shell, with *.sh applying to all Bourne/POSIX compatible shells and other extensions applying to that particular shell.
Solution 2:
.profile
.profile is for things that are not specifically related to Bash, like environment variables PATH and friends, and should be available anytime.
For example, .profile should also be loaded when starting a graphical desktop session.
.bashrc
.bashrc is for the configuring the interactive Bash usage, like Bash aliases, setting your favorite editor, setting the Bash prompt, etc.
.bash_profile
.bash_profile is for making sure that both the things in .profile and .bashrc are loaded for login shells.
For example, .bash_profile could be something simple like
. ~/.profile
. ~/.bashrc
If you were to omit .bashrc, only .profile would be loaded.
Solution 3:
According to the bash man page, .bash_profile is executed for login shells, while .bashrc is executed for interactive non-login shells.
So, what is a login or non-login shell?
When you login (type username and password) via console, either sitting at the machine, or remotely via ssh: .bash_profile is executed to configure your shell before the initial command prompt.
But, if you’ve already logged into your machine and open a new terminal window (xterm) inside Gnome or KDE, then .bashrc is executed before the window command prompt. .bashrc is also run when you start a new bash instance by typing /bin/bash in a terminal.
An exception to the terminal window guidelines is Mac OS X’s Terminal.app, which runs a login shell by default for each new terminal window, calling .bash_profile instead of .bashrc. Other GUI terminal emulators may do the same, but most tend not to.
More here.