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Unformatted text preview: tes the source program in extended language to a standard
language source program by using the preprocessor, and the second pass translates
the standard language source program to executable object code by using the
standard language compiler. But in most cases of preprocessing, the user is given
the feel of one-pass translation through creation of a library of system commands
that, when invoked, runs through the multiple operations in response to a short
sequence of keystrokes or one click of a picking device.
Command statements are used to instruct a computer to do some job. For example,
a "run" or "exec" statement may be used to execute a program and a "copy"
statement may be used to copy a file from one storage device 1 another. Often a
user needs to execute a set of commands to perform a particular task. For example,
to perform task, the user may be required to execute two independent programs,
and after execution of the first program he/she may be required to copy the output
file of the first program on to a device from which the second program expects the
input. So in this case, the user needs to specify two execute commands for
executing the two programs and a copy command before the second execute
command. A scripting language is a programming language that allows
programmers to integrate several such commands into a single command so that
the programmer need not type all the commands every time he/she needs to
perform the intended task. A program written in a scripting language is commonly
referred to as a script. Scripting languages support variables and simple control
structures to allow programmers to write scripts, which can conditionally execute or repeat the execution of certain commands. With these features, scripting
languages may be used to define complex commands execution patterns.
Another common use of scripting languages is in specifying execution
environment setup for applications that are quite complex, yet flexible enough* to
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This document was uploaded on 04/07/2014.
- Spring '14