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# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br>
# Set execute permissions for this shell script and run your shell script by issuing: <span style="color:blue;font-weight:bold;font-family:courier;">./for-6.bash</span><br><br>What do you notice? You should have noticed an '''error message'''.<br><br>
# To demonstrate what went wrong, <u>issue</u> the following '''commands''':<br><br><span style="color:blue;font-weight:bold;font-family:courier;">num1=5;num2=10<br>result=$num1+$num2<br>echo $result<br><br></span>Notice that the user-defined variable stores the text "'''10+5'''" which is <u>NOT</u> the expected result of adding the number 10 and 5.<br><br>As you may recall in class, we need to convert a number stored as text into a '''binary number''' for calculations (in this case, advance the value by 1 for each loop). We can accomplish this by either using the expr command, or by surrounding our math operation within a set of two round brackets.construct '''(( ))'''<br><br># To demonstrate, <u>issue</u> the following set of '''commands''':<br><br><span style="color:blue;font-weight:bold;font-family:courier;">num1=5;num2=10<br>sum=$(expr ($num1+$num2))<br>echo $sum<br><br>((product=$num1*$num2))<br>echo $product</span><br><br>Let's correct our '''for-6.bash''' shell script to correctly use math operations.<br><br>
# Use a text editor like vi or nano to edit the text file called '''for-6.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi for-6.bash</span>)<br>If you are using the nano text editor, refer to notes on text editing in a previous week in the course schedule.<br><br>
# Edit '''line 6''' and change to the following:<br><span style="font-family:courier;font-weight:bold;">((value=value+1))</span><br><br>'''Note:''' For those familiar with other programming languages, you can achieve the same results by using: '''((value++))'''<br><br>
