Loop to check if command line arguments are even or odd numbered....HELP!

[IbuntYOU]

I want to write a script to check if the command line has arguments. If it doesn't it will issue an error msg.

If the script is run with an argument say " /home>script.bash 2"
it will then run through a loop to check if the number is even or odd.

If its even it will print a msg and exit. If its odd, it will prompt the user to re-enter an even number.

Here is where I am stuck, once the user enters in a new number I want the script to then check if its even or odd, if it is odd I want it to loop until an even number is entered.

This is what I have so far, for the most part it works. Just the last stage to have the user re-enter a number then loop if its odd... doesn't work

Any help is much appreciated.



#!/bin/bash

if [ $# -le 0 ]; then
echo "USAGE: $0 [number]" >&2
exit 1
fi

for x

do

out=$(( $x % 2 ))
if [ $out -eq 0 ]
then
echo "The EVEN number is: $x"
exit 1
fi



echo "Number is NOT even..."
read -p "Please enter an EVEN numer:" num
echo "The EVEN number is: $num"


done



Thanks.

[WuNMOjTIQanXWBcH]

If the script is run with an argument say " /home>script.bash 2" it will then run through a loop to check if the number is even or odd.

If its even it will print a msg and exit. If its odd, it will prompt the user to re-enter an even number.
[…]
Just the last stage to have the user re-enter a number then loop if its odd... doesn't work
[…]

for x; do
	out=$(( $x % 2 ))
	if [ $out -eq 0 ]; then
		echo "The EVEN number is: $x"
		exit 1
	fi

	echo "Number is NOT even..."
	read -p "Please enter an EVEN numer:" num
	echo "The EVEN number is: $num"

done

Thereʼre a couple of comments I have on this piece of code:

• Please use CODE tags.
  
• Somewhere in this code an actual loop is missing. There really is no loop. The
  

  for x; do
  	[…]
  done

  construct loops through all the CLI arguments of the script, which, in your case of a single parameter, is not a loop. Maybe you wanted to place the loop somehwere in the last echo-read-echo block?
  
• Every variable inside of a "$(( … ))" construct is evaluated once. So "$(( x % 2))" is fine.

[IbuntYOU]

Hey,

Thanks for the reply, but I am still a little lost as to how and where to run the loop. Do I need a while?

How do i set it up so the last section just loops until an even number is re-entered?


thanks.

[WuNMOjTIQanXWBcH]

Do I need a while?

Most certainly.

How do i set it up so the last section just loops until an even number is re-entered?

Well, this would be a solution (though it doesnʼt protect against illegal input like letters or the like):

[…]
	num=1;
	while [ "$((x % 2))" -eq 1 ]; do
		echo "Number is NOT even…";
		read -p "Please enter an EVEN number: " num;
	done
	exit 1;
[…]

[IbuntYOU]

Most certainly.


Well, this would be a solution (though it doesnʼt protect against illegal input like letters or the like):

[…]
	num=1;
	while [ "$((x % 2))" -eq 1 ]; do
		echo "Number is NOT even…";
		read -p "Please enter an EVEN number: " num;
	done
	exit 1;
[…]

Thank you very much for your help! I was able to piece everything to together and get it to work!