Unix Shell Scripting, detecting the enter key

WinterSt · 08-31-2004, 02:13 AM

Hello, this is my first post so hello everyone!

I am writing a script with a menu that will return an error message if the user does not pick one of the valid options, and another if the user just presses the enter key.

Is it possible to use a while loop to detect if the user has only hit the enter key?
Below is a sample of the code I used when try to catch the enter key.

Code:

#!/bin/sh

read userInputTest
while [ "$userInpurtTest" != "[Enter]" ]
do
\t "echo you did not make a selection"
done

Thank you.

jlliagre · 08-31-2004, 03:11 AM

Code:

#!/bin/sh
while read userInputTest
do
   [[ -n "$userInputTest" ]] && break
   echo you did not make a selection
done

WinterSt · 08-31-2004, 04:18 AM

sorry that code does not work for me in the bourne shell I am using.

I get the following error

"tester.sh: [[: not found"

I guess I would like to know if I can catch the enter key by using read, placing it in a variable and then run a check on the variable to see if the user has pressed only the enter key.

Proud · 08-31-2004, 04:29 AM

I think the point is that the enter key isnt something you can explicitely test for, but the lack of any text on the entered line implies it, so test for that instead.

WinterSt · 08-31-2004, 04:48 AM

Thanks for pointing me in the right direction, in the end I used [ -z "$userInputTest" ] checks if $userInputTest is null.

Code:

read userInputTest
if [ -z "$userInputTest" ]; then
	echo "Selection not entered.\nPress Enter to continue \c"; read dummy
else echo "Invalid code!\nPress Enter to continue \c"; read dummy
fi

jlliagre · 08-31-2004, 10:27 AM

Quote:

sorry that code does not work for me in the bourne shell I am using.

OK, just use bash or ksh instead:

Code:

#!/bin/bash
while read userInputTest
do
   [[ -n "$userInputTest" ]] && break
   echo you did not make a selection
done

If you need to use the good old bourne shell, here's the fix:

Code:

#!/bin/sh
while read userInputTest
do
   test -n "$userInputTest" && break
   echo you did not make a selection
done

infernal · 09-01-2004, 06:06 AM

try this. I verified myself and it works:

Code:

#!/bin/sh

while :; do
        read tmp
        if [ -z "$tmp" ]; then
                echo "empty string!!"
        else
                break
        fi
done

WinterSt · 09-01-2004, 08:27 AM

Thanks. The problem has been solved.