For this lab, you will write a shell script called nethelper.sh that: 1. Reads in a list of hosts from a host file that is passed in as a parameter 2. Repeatedly, until the user selects quit (q), ask the user if the user wants to ping a host or look up a hosts DNS name 3. Once the user has selected an action, prompts the user for which host and then applies the action. Note that for the ssh action, the script must also ask the user for the user name that will be used to log into the host. Step 1 To accomplish step 1 above (reading in a list of hosts from a file), you will write a function called read_hosts. Functions in bash scripts have the following syntax: function name { # function body goes here } You can put any bash syntax inside the function as the function body. Also, note that the parameters to a function act like the parameters passed in at the command line. In other words, the parameters to the function are place in variable named $1, $2, and so on. So, how do you read the hosts from a file? The file will be formatted as one host per line. Therefore, you can simply use cat to print the file, capture the output, and the iterator over the output using a for loop. However, you will have to put the hosts in an array called hosts_array. Bash array are simple. You simply use the brackets to indicate an index. So, the algorithm for your function will look like the following: function read_hosts 1. set variable hosts to the results of calling cat on $1 (the name of the file passed as a parameter) 2. initialize a count variable to 1 (count will be the index into the array) 3. for each host in hosts do the following: 1. hosts_array[$count]=$host 2. add 1 to count To call the function, your script will simply execute the following code: read_hosts $@ The $@ passes the script parameter (the name of the file containing the hosts) to the function. In the above algorithm, hosts_array is a global variable, so the function's caller will be able to use the global variable to access the host names. Step 2 and 3 To implement step 2, you need a while loop. Before the loop, create a variable called done so the loop knows when to exit. In the body of the loop, print the menu (using echo, of course), then read the user's response. Next, use a case statement to determine which menu item the user chose (either a P, S, T, N, or Q). The case statement should execute the correct command based on the user's choice. For example, if the user chooses P, the script should run the ping command like so: ping -c 1 ${hosts_array[$which_host]} However, before you run ping, you should print the list of hosts, and ask the user to pick the host that the user wishes to include in the command. You will write a function called pick_host that allows the user to select a host. The algorithm for pick_host is as follows: function pick_host 1. set variable count to 1 2. for each host in $1 (where $1 is the list of hosts passed it - not the array) 1. echo "$count) $host" 2. add 1 to count 3. prompt the user to enter a number to select a host 4. read the user's response into the which_host variable 5. make sure that $which_host is greater than or equal to 1 but less than $count (it is a valid host in the array). If it is not, exit with an error message. The algorithm for the rest of steps 2 and 3 are as follows: while done == 0 1. echo P for ping or N for nslookup 2. prompt user for response 3. read response into variable cmd 4. call read_hosts function 5. case $cmd in P|p) pick_host "$hosts" echo "ping -c 1 ${hosts_array[$which_host]}" ping -c 1 ${hosts_array[$which_host]} ;; N|n) pick_host "$hosts" echo "nslookup ${hosts_array[$which_host]}" nslookup ${hosts_array[$which_host]} ;; Q|q) done=1; ;; *) echo "Bad choice"; ;; esac done
For this lab, you will write a shell script called nethelper.sh that:
1. Reads in a list of hosts from a host file that is passed in as a parameter
2. Repeatedly, until the user selects quit (q), ask the user if the user wants to ping a host or look up a hosts DNS name
3. Once the user has selected an action, prompts the user for which host and then applies the action. Note that for the ssh action, the script must also ask the user for the user name that will be used to log into the host.
Step 1
To accomplish step 1 above (reading in a list of hosts from a file), you will write a function called read_hosts. Functions in bash scripts have the following syntax: function name { # function body goes here }
You can put any bash syntax inside the function as the function body. Also, note that the parameters to a function act like the parameters passed in at the command line. In other words, the parameters to the function are place in variable named $1, $2, and so on.
So, how do you read the hosts from a file? The file will be formatted as one host per line. Therefore, you can simply use cat to print the file, capture the output, and the iterator over the output using a for loop. However, you will have to put the hosts in an array called hosts_array. Bash array are simple. You simply use the brackets to indicate an index. So, the
function read_hosts
1. set variable hosts to the results of calling cat on $1 (the name of the file passed as a parameter)
2. initialize a count variable to 1 (count will be the index into the array)
3. for each host in hosts do the following:
1. hosts_array[$count]=$host
2. add 1 to count
To call the function, your script will simply execute the following code:
read_hosts $@
The $@ passes the script parameter (the name of the file containing the hosts) to the function. In the above algorithm, hosts_array is a global variable, so the function's caller will be able to use the global variable to access the host names.
Step 2 and 3
To implement step 2, you need a while loop. Before the loop, create a variable called done so the loop knows when to exit. In the body of the loop, print the menu (using echo, of course), then read the user's response. Next, use a case statement to determine which menu item the user chose (either a P, S, T, N, or Q). The case statement should execute the correct command based on the user's choice. For example, if the user chooses P, the script should run the ping command like so:
ping -c 1 ${hosts_array[$which_host]}
However, before you run ping, you should print the list of hosts, and ask the user to pick the host that the user wishes to include in the command. You will write a function called pick_host that allows the user to select a host. The algorithm for pick_host is as follows:
function pick_host
1. set variable count to 1
2. for each host in $1 (where $1 is the list of hosts passed it - not the array)
1. echo "$count) $host"
2. add 1 to count
3. prompt the user to enter a number to select a host
4. read the user's response into the which_host variable
5. make sure that $which_host is greater than or equal to 1 but less than $count (it is a valid host in the array). If it is not, exit with an error message.
The algorithm for the rest of steps 2 and 3 are as follows:
while done == 0
1. echo P for ping or N for nslookup
2. prompt user for response
3. read response into variable cmd
4. call read_hosts function
5. case $cmd in
P|p)
pick_host "$hosts"
echo "ping -c 1 ${hosts_array[$which_host]}"
ping -c 1 ${hosts_array[$which_host]} ;;
N|n)
pick_host "$hosts"
echo "nslookup ${hosts_array[$which_host]}"
nslookup ${hosts_array[$which_host]} ;;
Q|q)
done=1;
;;
*) echo "Bad choice";
;;
esac
done
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