What is the difference between Multi-tasking and Multi-user environment?

In a Multi-tasking environment, same user can submit more than one tasks and operating system will execute them at the same time.

In a Multi-user environment, more than one user can interact with the operating system at the same time.

  1. What is Command Substitution in Unix?
    Command substitution is a mechanism by which Shell passes the output of a command as an argument to another command. We can even use it to set a variable or use an argument list in a for loop.

E.g. rm cat files_to_delete
In this example files_to_delete is a file containing the list of files to be deleted. cat command outputs this file and gives the output to rm command. rm command deletes the files.

In general Command Substitution is represented by back quotes `.

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