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<P align=center><I><B><A
href="http://www.cs.ncl.ac.uk/modules/2003-04/csc842/LinuxTut/index.htm">Home</A>
- <A
href="http://www.cs.ncl.ac.uk/modules/2003-04/csc842/LinuxTut/linux1.htm">(1)
Shells</A> - <A
href="http://www.cs.ncl.ac.uk/modules/2003-04/csc842/LinuxTut/linux2.htm">(2)
Files & Directories</A> - <A
href="http://www.cs.ncl.ac.uk/modules/2003-04/csc842/LinuxTut/linux3.htm">(3)
Processes</A> - <A
href="http://www.cs.ncl.ac.uk/modules/2003-04/csc842/LinuxTut/linux4.htm">(4)Shell
scripting</A> - <A
href="http://www.cs.ncl.ac.uk/modules/2003-04/csc842/LinuxTut/linux5.htm">(5)Makefiles</A></B></I></P></TD></TR>
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<TD width=577><FONT face="Times New Roman" size=5>Linux Tutorial - User's
view (4)</FONT>
<P><FONT face="Times New Roman">Subject Summary</FONT></P>
<OL>
<LI><FONT face="Times New Roman">Input & output</FONT>
<LI><FONT face="Times New Roman">Variables</FONT>
<LI><FONT face="Times New Roman">Maths</FONT>
<LI><FONT face="Times New Roman">Loops & if statement</FONT>
</LI></OL>
<P><FONT face="Times New Roman" size=5><B><I>Scripts</I></B></FONT></P>
<P>A term for macro or batch file, a script is a list of commands that can
be executed with or without user interaction. A script language is a
simple programming language with which you can write scripts.</P>
<P>We can write scripts and with the aid of the shell, we can execute
them.</P>
<P><FONT size=4>1. Hello World!</FONT></P>
<P>All scripts should be contained in a file, with this file given
executable privileges (Linux Tutorial - User's view (1) for information on
how to do this. Any text editor will do. <B>Emacs</B> is a popular editor
and should be available on most systems (simply type <B>emacs</B> at the
command line to get the editor). Editors with a graphical interface are
easiest to use for beginners. Ask your system administrator where the
graphical text editor is located. If you think you will become a hardened
computer user then <B>vi</B> can be used.</P>
<UL type=circle>
<LI><B>#!/bin/sh </B>
<LI><B>echo "Hello" </B>
<LI><B>echo "World" </B> </LI></UL>
<P>The above script prints out on the screen (via the echo command) "Hello
Word". Notice that the first line of the script is actually a special line
of code that indicates the shell that is required to parse this script to
execute it successfully. </P>
<P><FONT size=4>2. Variables</FONT></P>
<P>Variables (user defined in the script and environmental) may be used
within scripts. Consider the following script:</P>
<UL type=circle>
<LI><B>#!/bin/sh </B>
<LI><B>echo "Hi there"</B>
<LI><B>echo "Type in your real name Slim Shady?"</B>
<LI><B>read ENM</B>
<LI><B>echo "Hello $ENM"</B> </LI></UL>
<P>Here we have defined a variable called <B>ENM</B> and used it to store
some user input. Notice how the <B>read</B> command is used to gain the
user interaction.</P>
<P><FONT size=4>3. Maths</FONT></P>
<P>Scripts may also carry out simple arithmetic for you. Consider the
following:</P>
<UL type=circle>
<LI><B>#!/bin/sh</B>
<LI><B>if [ "$2" ]</B>
<LI><B>then</B>
<LI><B>answer=`expr $1 + $2`</B>
<LI><B>echo "Answer = $answer"</B>
<LI><B>else</B>
<LI><B>echo "This script needs two arguments"</B>
<LI><B>fi</B>
<LI><B>echo "Finished"</B> </LI></UL>
<P><FONT size=4>4. Loops</FONT></P>
<P>In programming environments it is always useful to enable a programming
structure that allows for a repetition of a task without actually typing
this task out multiple times. Scripts provide this mechanism via looping
structures. The while loop is commonly used in scripts:</P>
<UL type=circle>
<LI><B>#!/bin/sh</B>
<LI><B>dayname=1</B>
<LI><B>while [ $dayname -le 7 ]</B>
<LI><B>do</B>
<LI><B>echo "Day number is $dayname"</B>
<LI><B>dayname=`expr $dayname + 1`</B>
<LI><B>done</B>
<LI><B>echo "Finished"<BR></B></LI></UL>
<P>The dayname=1 creates a variable called <B>dayname</B> and places the
number <B>1</B> into it. The <B>while</B> command executes all the
commands between the <B>do</B> and the <B>done</B> repetitively until the
`` test'' condition is no longer true (i.e until <B>dayname</B> is no
longer less than 7. The <B>-le</B> stands for -less-than-or-equal-to.</P>
<P><FONT size=4>5. If statement</FONT></P>
<P>Sometimes it is required that a choice of execution be made in a script
depending on some influence of the environment (e.g., user choice). The if
statement satisfies this requirements in scripting:</P>
<UL type=circle>
<LI><B>#!/bin/sh </B>
<LI><B>if [ ⌨️ 快捷键说明
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