Inputing variables to awk script - shell

Question

I am working on a script that detects CDP information from the network card. The script currently works on my computer, but i would like to make it available for other people. The script currently runs because in the code it has the name of my network card. I would like to make it ask for the network card name (perhaps list the ones available) before running the script. My code is:
#!/usr/bin/awk -f
function red(s) {
printf "\033[1;31m" s "\033[0m "
}
function green(s) {
printf "\033[1;32m" s "\033[0m "
}
function blue(s) {
printf "\033[1;34m" s "\033[0m "
}
BEGIN{
cmd = "tcpdump -nvi enp0s25 -s 1500 ether dst 01:00:0c:cc:cc:cc -c 1"
while ((cmd | getline) > 0) {
str="Device-ID:Cisco IOS Software:Port-ID:VTP:Address:VLAN:Duplex:VoIP:"
split(str,s,":")
for(i=1;i<=length(s);i++){
if ($0 ~ s[i] && s[i]){
if (i==1){
print "\n";
print red("Device Name: ") green($7);
}
else if (i==2){
print red("Software Version: ") green($0) ;
}
else if (i==3){ /*Port*/
print red($1 ": ") green($7);
}
else if (i==4){
print red($1 " " $2 " " $3 ": ") green($9);
}
else if (i==5){
print red("IP Address: ") green($9);
}
else if (i==6){
print red("VLAN: ") green($9);
}
else if (i==7){
print red("DUPLEX: ") green($7);
}
else if (i==8){
print red("Voice VLAN: ") green($13);
}
else{
s[i]=0;print " "}
}
}
}
}
As you can see, it runs the command with my NIC which is enp0s25. I need to make this a variable, that is entered by the user (maybe only once). the best approach would be to enumerate the cards and have the user pick the card he wants using a number. I have NO IDEA how to do this.

Answer 1

You're making life harder for youself by trying to use awk as a shell by encoding the call to tcpdump inside awk. Think about that - you're writing a shell script to call awk to call shell to call tcpdump instead of just having shell call tcpdump and pipe the output to awk.
Just write your shell script as:
tcpdump ... enp0s25 ... | awk 'script'
and then you can tweak it in the obvious way:
echo "enter a nic: "
IFS= read -r nic
tcpdump ... "$nic" ... | awk 'script'

Answer 2

#!/usr/bin/awk -f
function red(s) {
printf "\033[1;31m" s "\033[0m "
}
function green(s) {
printf "\033[1;32m" s "\033[0m "
}
function blue(s) {
printf "\033[1;34m" s "\033[0m "
}
function detectNic( ) {
printf "Enter the Ethernet card to listen or press enter to listen
to Default:";getline nic<"/dev/tty"
if (nic == ""){
command = "cat /var/defaultnic"
nic = command | getline
print "Default network card to listen: " $nic
return $nic
}
else{
return nic
}
}
BEGIN{
nic = detectNic();
cmd = "tcpdump -nv -s 1500 ether dst 01:00:0c:cc:cc:cc -c 1 -i"
while ((cmd nic | getline) > 0) {
str="Device-ID:Cisco IOS Software:Port-ID:VTP:Address:VLAN:Duplex:VoIP:"
split(str,s,":")
for(i=1;i<=length(s);i++){
if ($0 ~ s[i] && s[i]){
#DEVICE ID
if (i==1){
print "\n";
print red("Device Name: ") green($7);
}
#SOFTWARE VERSION
else if (i==2){
print red("Software Version: ") green($0) ;
}
#PORT
else if (i==3){
print red($1 ": ") green($7);
}
#VTP DOMAIN
else if (i==4){
print red($1 " " $2 " " $3 ": ") green($9);
}
#IP ADDRESS
else if (i==5){
print red("IP Address: ") green($9);
}
#CURRENT VLAN
else if (i==6){
print red("VLAN: ") green($9);
}
#DUPLEX
else if (i==7){
print red("DUPLEX: ") green($7);
}
#VOICE VLAN
else if (i==8){
print red("Voice VLAN: ") green($13);
}
else{
s[i]=0;print " "}
}
}
}
}