EECS 1012 Lecture Notes - Lecture 21: Bourne Shell, Shell Script
13 Jun 2018
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EECS 1012 Lecture 21 Notes
Introduction
The Elements of a Command Language
• In addition to the usual commands, the UNIX and Linux shells contain a set of powerful
utility commands and other features that allow the creation of very sophisticated
command programs.
• In UNIX and Linux, shell scripts are a fundamental way of getting work done.
• Shell scripts can be executed just as if they were programs
• In fact, due to the power of the shell script language, it is frequently possible to avoid
writing a normal program by using a shell script instead.
• You’e alread see a eaple of a Windows command language script that assists the
user in performing a routine computer task.
• Many Linux operating system operations are, in fact, shell scripts.
• Shell scripts often can be used in place of a conventional program, as well.
• The example shown 9 is a UNIX Bourne shell program that determines the nearest major
airport to an arbitrary city entered by the user.
• Scripting languages are expanded forms of command languages, often encompassing
features well beyond those found in a standard command language.
• Some scripting languages even provide portability between different operating systems.
• Perl, JavaScript, PHP, and Python are examples of portable scripting languages.
• Like any programming language, there are certain elements in a command language
that affect the usefulness of the language.
• The choice of commands and utilities is an important consideration, but it is not the only
consideration.
• There are other features that enhance the value of a language.
• These are some of the most important features of a command language
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