Solution:

It is impossible to describe all the "." files, but here is a partial list, starting with the one you specifically asked about:

.sh_history
The shell ksh keeps a command history. This allows you to retrieve, edit and re-execute previously entered commands. Pressing the ESC key, followed (usually) by vi like commands allows you to access this function. It is possible to configure the shell to use Emacs like commands to edit the history. The file is used by the shell as a buffer for the shell history. The environment variables HISTFILE and HISTSIZE govern the behavior of this function. They are described in the ksh manual page.

.profile
Your login profile. This is simply a script of shell commands executed each time you login. .kshrc like .profile, this is a script of commands. It is executed each time you start a shell (i.e. even if you "shell escape" within vi). .kshrc is unique to the shell ksh. .profile exists for sh and ksh, while csh uses .login and .cshrc files.

.newsrc
Your news subscription list.

.mailrc
A list of commands executed by mail each time you run it. Useful for entering aliases. This file is NOT used by the ELM mail reader.

.signature
A text file of not more than 4 lines appended to the end of any message posted to news. In general, a number of system programs and other programs make use of "." files as configuration and startup files.

Why "." files? If you notice, ls does not show these files by default - they are somewhat hidden. Other than this, the "." files have no special significance. It is simply convention that programs use them in this manner - rn, for example, could have just as easily use the file name "fred" to keep your subscription list.

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