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.
An embedded system is a dedicated computer system designed for one or two specific functions. This system is embedded as a part of a complete device system that includes hardware, such as electrical and mechanical components. The embedded system is unlike the general-purpose computer, which is engineered to manage a wide range of processing tasks. Because an embedded system is engineered to perform certain tasks only, design engineers may optimize size, cost, power consumption, reliability and performance. Embedded systems are typically produced on broad scales and share functionalities across a variety of environments and applications.
Embedded systems are managed by single or multiple processing cores in the form of microcontrollers or digital signal processors (DSP), field-programmable gate arrays (FPGA), application-specific integrated circuits (ASIC) and gate arrays. These processing components are integrated with components dedicated to handling electric and/or mechanical interfacing. An embedded system's key feature is dedication to specific functions that typically require strong general-purpose processors. For example, router and switch systems are embedded systems, whereas a general-purpose computer uses a proper OS for routing functionality. However, embedded routers function more efficiently than OS-based computers for routing functionalities. Commercial embedded systems range from digital watches and MP3 players to giant routers and switches. Complexities vary from single processor chips to advanced units with multiple processing chips.
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