Inputing variables to awk script

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.

Why are you bypassing awks normal mode of operation (e.g. tcpdump args | awk 'script') and hard-coding a getline loop instead? — Ed Morton
– Ed Morton, Commented Jul 20, 2017 at 12:52
I'll come back to your actual question later, but you're using printf wrong: if the string contains % sequences, you'll get an error. You need to keep the parameter out of the format string. I would do function colorize(s, n) { printf "\033[1;%dm%s\033[0m ", n, s } then function red(s) {colorize(s, 31)}, etc — glenn jackman
– glenn jackman, Commented Jul 20, 2017 at 13:03

Ed Morton · Accepted Answer · 2017-07-20 12:56:32Z

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'

answered Jul 20, 2017 at 12:56

Ed Morton

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yurividal · Accepted Answer · 2017-07-20 11:53:00Z

0

#!/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 "   "}
                }  
            }
        }
}

answered Jul 20, 2017 at 11:53

yurividal

1779 bronze badges

1 Comment

Ed Morton Over a year ago

nic = command | getline; return $nic sets nic to the result status of (i.e. NOT the value detected by) the getline call (-1, 0, or 1) and then returns the field or record at that position ($-1, or $0, or $1). Probably not what you're trying to do. And catting the file to a pipe to getline instead of just reading the file with getline like you did a couple of lines earlier (getline nic<"/dev/tty") doesn't make sense. Check for errors on the getline calls to avoid obscure, silent failures. See awk.freeshell.org/AllAboutGetline. Finally - don't do it this way at all, awk is not shell

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