#!/bin/sh
#
# 6/7/2017
#
echo "Chapter 9 - Script 3"

if [ $# -ne 1 ] ; then
 echo "Usage: script3 parameter"
 exit 255
fi

parm=$1
echo "parm: $parm"

if [ "$parm" = "home" ] ; then
 echo "parm is home."
elif if [ "$parm" = "cls" ] ; then
 echo "parm is cls."
elif [ "$parm" = "end" ] ; then
 echo "parm is end."
else
 echo "Unknown parameter: $parm"
fi

echo "End of script3"
exit 0

Here's the output:

Did you find my mistake? When I code an if...elif...else statement, I tend to copy and paste the first if statement. I then prepend elif to the next statement but forget to remove the if. This gets me almost every time.

Look at how I ran this script. I started first with just the name of the script to invoke the Usage clause. You may find it interesting that the syntax error was not reported by the interpreter. That's because it never got down to that line. This can be a real problem with scripts, as it may run for days, weeks, or even years before running a part of code that has a syntax error in it and then failing. Keep this in mind when writing and testing your scripts.

Here is another quick example of a classic syntax error (classic in the sense that I just now made it again):

for i in *.txt
 echo "i: $i"
done

When run it outputs this:

./script-bad: line 8: syntax error near unexpected token `echo'
./script-bad: line 8: ` echo "i: $i"'

Can you find my mistake? If not look again. I forgot the do statement after the for statement. Bad Jim!

One of the easiest things to do wrong in a script is to forget the $ in front of a variable. This is particularly so if you code in other languages such as C or Java, because you don't prepend a $ to variables in those languages. The only real advice I can give here is if your script just doesn't seem to be doing anything right check all of your variables for the $. But be careful you don't go too far and start adding them where they don't belong!