Shell script to specify a user is logged into computer - shell

Question

username=$1
freq=$2
checkuser()
{
if who grep "$1"
then
sleep 60
fi
}
if [ -n "$1" ]
then
echo "Enter username"
read username
checkuser
echo -e "$1 is logged on \a"
echo -e "$1 logged in at `date`">>LOG
checkuser
else
echo "User is not logged on"
fi
I need to integrate a second argument into my code which allows for the user to specify after what time should the script check to see who is logged in. I have it set to 60 seconds currently and this needs to be the default frequency. I tried to use another function but to no avail. I thought of something like this...
if [ "$2" -ne 0 ]
then
freq=$2
else
freq=60
Thanks William for that was very helpful!! I changed the code a bit and came up with this. I now need to add a 3rd argument "X" which when selected just sends a message to the LOGFILE and not to the screen. I made an attempt but not doing as intended.
username=$1
freq=${2:-10}
X=$3
checkuser()
{
whoami|grep "$1";
}
while checkuser "$username"
do
echo -e "$1 is logged on \a"
echo "$1 logged in at `date`">>LOGFILE
sleep $freq
exit 0
done
echo "User is not logged in"
if [ "$3" -ne 1 ]
then
echo "$1 logged in at `date`"LOGFILE
fi

Answer 1

username=$1
freq=${2:-60} # Set a default frequency
checkuser(){ who | grep -q "$1"; }
while ! checkuser "$username"; do
echo "User is not logged on"
sleep $freq
done
echo "$1 is logged on"
Also note that you can simplify the setting of username:
username=${1:-$( echo "Enter username: "; read u; echo $u; )}

Answer 2

echo 'Enter id'
read id
res=`who | grep "$id" | wc -l`
if [ $res -eq 0 ]
then
echo 'user is not logged in'
else
echo 'user is logged in'
fi

Answer 3

A simple shell script that takes the username as input and determines whether the user is currently logged in.
if [[ $# -eq 0 ]]; then
echo "Usage: " $0 "username"
exit 1
fi
result="$(who | grep $1 | wc -l)"
if [[ $result -gt 0 ]]; then
echo "$1 is currently logged in"
else
echo "$1 is not logged in"
fi
exit 0