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Bash : While Loop behavior

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# 1  
Old 02-12-2015
Bash : While Loop behavior
Good Morning

I think there may be something I dont understand fully.

The following code works well, but I dont like the set domen method.

Code:
#!/bin/bash
#
domen="y"
while [ "$domen" == "y" ]
do
echo " M A I N - M E N U"
echo "1. Contents of /etc/passwd"
echo "2. List of users currently logged"
echo "3. Prsent handling directory"
echo "4. Exit"
echo "Please enter option [1-4] : "
read theopt
echo $theopt
case $theopt in
1) echo $opt;;
2) echo $opt;;
3) echo $opt;;
4) exit 0;;
*) echo "Bad opt";;
esac
done


So I looked in one of my books (Written by Chris FA Johnson) and on the web for a second example. The following doesnt work. You'll have to run it to see what I mean. Ill try to explain. As I run through the menu options to test, at one point or another, my option isnt read and the behavior is kind of like a back space. Even when using -n1 for read behavior was odd.


Code:
#!/bin/bash
#
while : 
do
echo " M A I N - M E N U"
echo "1. Contents of /etc/passwd"
echo "2. List of users currently logged"
echo "3. Prsent handling directory"
echo "4. Exit"
echo "Please enter option [1-4] : "
read theopt
echo $theopt
case $theopt in
1) echo $opt;;
2) echo $opt;;
3) echo $opt;;
4) exit 0;;
*) echo "Bad opt";;
esac
done

Chris' example does provide a function to do the reading of the options, but I want to understand whats going on here.

As usual thanks for the help !
Pop
Last edited by popeye; 02-12-2015 at 01:18 PM..
# 2  
Old 02-12-2015
In what way does it not work?


Code:
$ ./oneopt.sh
 M A I N - M E N U
1. Contents of /etc/passwd
2. List of users currently logged
3. Prsent handling directory
4. Exit
Please enter option [1-4] :
1
1

 M A I N - M E N U
1. Contents of /etc/passwd
2. List of users currently logged
3. Prsent handling directory
4. Exit
Please enter option [1-4] :
2
2

 M A I N - M E N U
1. Contents of /etc/passwd
2. List of users currently logged
3. Prsent handling directory
4. Exit
Please enter option [1-4] :
3
3

 M A I N - M E N U
1. Contents of /etc/passwd
2. List of users currently logged
3. Prsent handling directory
4. Exit
Please enter option [1-4] :
4
4

$

I see nothing wrong.
This User Gave Thanks to Corona688 For This Post:
popeye
# 3  
Old 02-12-2015
I can't replicate the error that you report. Did you consider bash's select builtin?
This User Gave Thanks to RudiC For This Post:
popeye
# 4  
Old 02-12-2015
I just realized something. By 'backspace' do you mean 'goes to the beginning of the line'? Your file may have carriage returns in it. What have you been editing it with?
This User Gave Thanks to Corona688 For This Post:
popeye
# 5  
Old 02-12-2015
I'd "double quote" the $variables so the script does not fail for all whitespace in or shell sensitive characters.

You read 'theopt' but echo 'opt', which is never set.

Usually ':' prompts have no linefeed, like: 'echo "Please enter option [1-4] : \c"' or use the 'read -p prompt' option.
This User Gave Thanks to DGPickett For This Post:
popeye
# 6  
Old 02-12-2015
VERY INTERESTING !

Ive tried this on a VM at school, a Ubuntu VM on my latptop and a Centos VM on my laptop.

What happens on all is that as I run through and test each option, at one point it seems that the read doesnt except input. It really behave like a backspace, but what I suspect is happening is that read is executing again. Kind of ignores input.

PS Stumped the instructor too !!!

---------- Post updated at 01:13 PM ---------- Previous update was at 01:05 PM ----------

I just tried to execute it on a work VM ... shhh dont tell the boss. Its running on that vserver. What the heck ? Only difference is that Im using VMPLAYER on my laptop and at school. .... scratching my head. Technical problem between chair and keyboard ??
# 7  
Old 02-12-2015
We will not know exactly what you mean unless you copy-paste the output of it misbehaving.

Also, from earlier:

Quote:
Originally Posted by Corona688
Your file may have carriage returns in it. What have you been editing it with?
This User Gave Thanks to Corona688 For This Post:
popeye
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