4 if [ $?

A penetration tester wants to use the following Bash script to identify active servers on a network:

1 network_addr="192.168.1"

2 for h in {1..254}; do

3 ping -c 1 -W 1 $network_addr.$h > /dev/null

4 if [ $? -eq 0 ]; then

5 echo "Host $h is up"

6 else

7 echo "Host $h is down"

8 fi

9 done

Which of the following should the tester do to modify the script?
A . Change the condition on line 4.
B . Add 2>&1 at the end of line 3.
C . Use seq on the loop on line 2.
D . Replace $h with ${h} on line 3.

View Answer

Answer: C

Explanation:

The provided Bash script is used to ping a range of IP addresses to identify active hosts in a network.

Here’s a detailed breakdown of the script and the necessary modification:

Original Script:

1 network_addr="192.168.1"

2 for h in {1..254}; do

3 ping -c 1 -W 1 $network_addr.$h > /dev/null

4 if [ $? -eq 0 ]; then

5 echo "Host $h is up"

6 else

7 echo "Host $h is down"

8 fi

9 done

Analysis:

Line 2: The loop uses {1..254} to iterate over the range of host addresses. However, this notation might not work in all shell environments, especially if not using bash directly or if the script runs in a different shell.

Using seq for Better Compatibility:

The seq command is a more compatible way to generate a sequence of numbers. It ensures the loop

works in any POSIX-compliant shell.

Modified Line 2:

for h in $(seq 1 254); do

This change ensures broader compatibility and reliability of the script.

Modified Script:

1 network_addr="192.168.1"

2 for h in $(seq 1 254); do

3 ping -c 1 -W 1 $network_addr.$h > /dev/null

4 if [ $? -eq 0 ]; then

5 echo "Host $h is up"

6 else

7 echo "Host $h is down"

8 fi

9 done