What is a shell?

Shells are interactive programs that provide a ``glue'' that fastens other programs together. They perform the following tasks:

• Execute the commands typed at the shell prompt.

• Find and execute other programs on command.

• Interpret the wildcard characters in filename specifications.

• Interpret complex regular expressions.

• Permit redirection of input and output.

• Construct pipelines containing several programs operating in sequence on the same data stream.

• Process shell scripts (a collection of shell commands that can control execution of other programs).

• Perform some basic tests on data and files.

Your work takes the form of a dialogue with your shell, which acts as the interface between you and the rest of the system. Like all good interfaces, your shell allows you to customize it to make life easier.