public/subjects/devops/in-back-ground

in-back-ground

Instructions

Create a script in-back-ground.sh which will execute a job in the background that will do the following:

• Run the command cat on the file facts which will read the contents of the file and print it to stdout.
• The output of the cat command will be piped to the grep command, which will search for the string "moon" in the file.
• If the grep command succeeds (if it finds the string "moon"):
  • You will print "The moon fact was found!" to the output.txt file. If it fails the file output.txt is not created.
  • You should also print the line which contains the string to the stdout.

You must do all these steps running only one job and using the command nohup!

Expected output:

$ ls
facts in-back-ground.sh
$ ./in-back-ground.sh
nohup: redirecting stderr to stdout
- Australia is wider than the moon. The moon sits at 3400km in diameter, while Australia's diameter from east to west is almost 4000km.
$ ls
facts in-back-ground.sh output.txt
$ cat output.txt
The moon fact was found!
$

$ ./in-back-ground.sh   # If the string isn't found
nohup: redirecting stderr to stdout
$ ls
facts in-back-ground.sh
$ cat output.txt
cat: output.txt: No such file or directory
$

In order to test your solution, you need to create your own facts file. This file must not be submitted!

Hints

The nohup command is used to run a command in the background, even if you close the terminal or log out of the system. When a command is run with nohup, it ignores the "SIGHUP" signal, which is sent to processes when the terminal they are running in is closed.

For example, to run the ls command in the background with nohup, you can use the following command:

$ nohup ls &

This will run the "ls" command in the background, and ignore the "SIGHUP" signal. The "&" symbol puts the "ls" command in the background, allowing the terminal to continue accepting input while the "ls" command is running.

In a Unix-like shell, stdin, stdout, and stderr are three standard streams that are used to communicate with a program or process.

• stdin (standard input) is a stream of data that a program or process reads from. By default, stdin is the keyboard, but it can be redirected to read from a file or the output of another command.

• stdout (standard output) is a stream of data that a program or process writes to. It can be redirected to write to a file or to the input of another command using the > operator.

• stderr (standard error) is a stream of data that a program or process writes to for error messages and other diagnostic output. It can also be redirected to write to a file or to the input of another command using the 2> operator.

You have to use Man or Google to know more about commands flags, in order to solve this exercise! Google and Man will be your friends!