Linux Shell (repost)

What is a shell and what does it do?
Research the internet for different shells and give a brief description of two that we have not worked with yet.

The shell is a program which takes your commands that you type on the keyboard and gives them to the operating system to execute. The shell interprets your commands (keystrokes) and runs the utilities or programs that you requested. The most common Linux shells are bash, sh, csh, and ksh. Linux is a multitasking operating system, so more than one shell can be running at a time. Each shell keeps its work isolated from the other shells that are running.

It appears that anyone with the knowledge can write a new shell. There are some compatibility issues to contend with. The main one seems to be POSIX which statnds for "Portable Operating System Interface". This is the open operating interface standard accepted world-wide. It is produced by IEEE and recognized by ISO and ANSI. POSIX support assures code portability between systems and is increasingly mandated for commercial applications and government contracts. ISO is the International Organization for Standardization and ANSI is the American National Standards Institute.

Two of the most interesting shells that we have not used yet are "resh" and "sash". The resh shell is a restricted version of the sh shell and is equivalent to sh -r. This allows users to copy files without having access to a shell on the server. There are many security risks when users are allowed access to another system, this is an attempt to secure ftp servers. The sash is a stand alone shell that was designed for recovering from a system failure. It is designed to be simple and robust, for people who need to do emergency repair work on a system.