How can i fix my functions in bash - bash

Question

I am new to bash scripting have patience.
I have this code where it scans ports of domains and shows them to the user and it works perfectly by it self but when i added functions to it gives me errors. What am I doing wrong here?
check_parms () {
case $# in
1) ports='1-1023'
host=$1 ;;
2) ports=$1
host=$2 ;;
*) echo 'Usage: portscan [port|range] host'
exit 1 ;;
esac
}
# check port range
check_ports () {
if [ "$(echo $ports | grep '^[1-9][0-9]*-[1-9][0-9]*$')" != "" ]; then
firstport=$(echo $ports | cut -d- -f1)
lastport=$(echo $ports | cut -d- -f2)
elif [ "$(echo $ports | grep '^[1-9][0-9]*$')" != "" ]; then
firstport=$ports
lastport=$ports
else
echo "$ports is an invalid port(s) value"
exit 2
fi
}
# check firstport > lastport
check_order () {
if [ $firstport -gt $lastport ]; then
echo $firstport is larger than $lastport
exit 3
fi
}
# check host value
check_host () {
regex='^([1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])){3}$'
if [ "$(echo $host | grep '[A-Za-z]')" != "" ]; then
response=$(host $host)
if [[ "$response" =~ "timed out" || "$response" =~ "not found" ]]; then
echo host $host not found
exit 4
fi
elif [[ ! $host =~ $regex ]]; then
echo $host is an invalid host address
exit 5
fi
}
# check if host is reachable using ping
check_ping () {
if [[ "$(ping -c 1 -W 2 -n $host)" =~ "0 received" ]]; then
echo $host is unreachable
exit 6
fi
}
# start the scan
do_scan () {
echo -n "Scanning "
for p in $(seq $firstport $lastport)
do
echo -n .
x=$((echo >/dev/tcp/$host/$p) >/dev/null 2>&1 && echo "$p open")
if [ "$x" != "" ]; then
y="${y}
$x"
fi
done
}
# show results of scan
show_results () {
echo -e "\n$y\n"
exit 0
}
check_parms $#
check_ports $ports
check_order $firstport $lastport
check_host $host
check_ping $host
do_scan $host $firstport $lastport
show_results

Answer 1

The way you're passing and using function arguments doesn't make sense. The one I see that's blatantly wrong is the first:
check_parms () {
case $# in
1) ports='1-1023'
host=$1 ;;
2) ports=$1
host=$2 ;;
*) echo 'Usage: portscan [port|range] host'
exit 1 ;;
esac
}
#... then in the main program:
check_parms $#
To understand the problem, suppose the main script is run with two arguments: "5-50" and "10.10.10.10". The line check_parms $# runs check_params and passes the number of arguments (2) as an argument to it. Fine so far. Then in check_params, it runs case $# in, but at this point we're inside check_params, so $# refers to the number of arguments passed to check_params, not the number passed to the main script. check_params was passed only one parameter (the number 2), so $# is 1, and it executes the 1) case, which sets ports to "1-1023" and host to "2". This is not what you wanted at all.
If you want check_params to be able to see the same parameters that were passed to the main script, you have to pass it those same parameters with check_params "$#".
The arguments passed to the other functions simply don't appear to be used; this won't necessarily cause trouble, but it makes for confusing code (and confusing code breeds bugs). Consider, for example the check_order function. You pass it $firstport and $lastport as arguments (meaning that within check_order, $1 is set to the value of $firstport and $2 is set to the value of $lastport), but then you don't use those arguments inside check_order; instead you use $firstport and $lastport directly, ignoring the parameters. Since they're the same thing, it doesn't really matter, but if someone later tried to use it for something else (check_order $currentport 1023) it would check $firstport and $lastport rather than what it looks like it should be checking.
Solution: change the functions to use their arguments rather than accessing global variables directly. (Or use the global variables explicitly and stop pretending to pass them as arguments; but globals are generally bad, so this is the worse option.) Something like this:
check_order () {
if [ $1 -gt $2 ]; then
echo $1 is larger than $2
exit 3
fi
}