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.
Exception handling is a mechanism in which a programming construct is used to consistently trap, intercept and handle the error occurred during application execution. The Common Language Runtime (CLR) of .NET Framework is designed to use an exception handling model based on exception objects and protected blocks of code.
The features of exception handling mechanism implemented in CLR are as follows:
a) Each language can have its own specification for handling exceptions without any restrictions
b) Exceptions are generated and handled irrespective of the language used and type of code (managed or unmanaged)
c) Exceptions can be thrown across process or machine boundaries
.NET runtime throws exceptions as objects derived from System.Exception class that contain error details, including message and line of code where the error occurred, etc. The construct "try..catch..finally" is used for exception handling. While "try" (where exceptions are anticipated) and “catch” (where exceptions are handled) blocks are mandatory, the "finally" (where code executed in any case) block is optional.
When compared to error handling implemented using traditional methods - like usage of return code as in Component Object Model (COM) and "go to" statements, as in Visual Basic, etc. - the main benefits of exceptions in .NET are trapping of all failures, elimination of process of checking return value and its usage (if invalid) in applications, usage in scenarios where there is no return value such as constructors, increased reliability and better performance.
While Java provides "checked" exceptions that help in preventing incidence of unhandled exceptions during compilation, they cannot be used for errors which are unrecoverable failure. Exception handling in C++ differs from that in .NET by not having the "finally" block for cleaning up resources and without any restriction for the type of exception.
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