# When prompted, enter a letter instead of a number. What happens?<br><br>Does the shell script allow you to enter an invalid grade like 200 or -6?<br><br>Let's add an additional error-checking loop to force the user to enter a number between 0 and 100.<br><br># Use a text editor like vi or nano to edit the text file called '''if-5.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi if-5.bash</span>)<br><br># Add the following lines in your shell script <u>AFTER</u> the read statement to prompt the user for a mark:<br><span style="font-family:courier;"><br>while [ $mark -lt 0 ] || [ $mark -gt 100 ]<br>do<br> &nbsp;&nbsp;&nbsp;read -p "Invalid number range. Enter a mark (0-100): " mark<br>done</span><br><br># Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br># Run your shell script by issuing:<br><span style="color:blue;font-weight:bold;font-family:courier;">./if-5.bash</span># When prompted, enter a letter instead of a number. What happens?<br>Does the shell script allow you to enter an invalid grade like 200 or -6?<br><br>

      :In the next investigation, you will ..learn to create and test-out start-up files to customize your shell.