Multiple choice technology operating systems

Whats the command to kill the last background job?

  1. kill $!
  2. kill $0
  3. kill $#
  4. kill -9 $1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In Unix/Linux shell scripting, the special variable $! contains the process ID (PID) of the last background job. The command kill $! sends a termination signal to that specific background process. Option B (\$0) refers to the shell script name, option C ($#) gives argument count, and option D incorrectly uses -9 with $1 (first positional parameter).

AI explanation

To answer this question, you need to understand how to kill background jobs in a Unix-like operating system.

The correct command to kill the last background job is option A) kill $!.

Explanation for each option:

Option A) kill $! - This option is correct because $! refers to the PID (Process ID) of the last background job. By using the "kill" command followed by $!, you can terminate the last background job.

Option B) kill \$0 - This option is incorrect because \$0 refers to the PID of the current shell process, not the last background job.

Option C) kill $# - This option is incorrect because $# refers to the number of command-line arguments, not the PID of the last background job.

Option D) kill -9 \$1 - This option is incorrect because \$1 refers to the first command-line argument, not the PID of the last background job. Additionally, using the -9 signal with the kill command is a forceful termination, which may not be necessary or desired.

Therefore, the correct answer is A) kill $!. This option is correct because it correctly references the PID of the last background job, allowing you to terminate it.

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