A shell variable is a variable that is available only to the current shell. In contrast, an environment variable is available system wide and can be used by other applications on the system.A shell is the operating system's command interpreter. It processes the commands entered on the command line or read from a shell script file.
Digital subscriber line (DSL) is a technology that transports high-bandwidth data over a simple telephone line that is directly connected to a modem. This allows for file-sharing, and the transmission of pictures and graphics, multimedia data, audio and video conferencing and much more. DSL uses the analog medium, which is reliable and prevents interruptions and heavy packet loss. DSL is fast and provides low user subscription rates.
DSL was originally part of the Integrated Services Digital Network (ISD) specification introduced in 1984. In the beginning, ISDN was being used for point-to-point connections for different kinds of data sharing. With the passage of time and the increasing size of networks, ISDN gave a low data speed because of various issues, from interruptions in telephone lines to natural factors like fog and rain. After the failure of ISDN, DSL emerged and started providing broadband connections over an analog medium with an efficient network environment. DSL mainly uses copper wires and fiber optic cables as its transmission medium.
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