diff command is used for converting one file into another in order to make them identical and comm is used for displaying the common elements in both the files.

Above output indicates that file01 contains 3 lines, 9 words and 45 characters.

Explanation: The chmod (change mode) command is used to change the permissions of files. This command can only be run by the owner of the file or by the super user.

Explanation: ‘:x’ command saves our content and quits the editor simultaneously. This command is invoked in ex-mode.

Explanation: We can escape to the shell without quitting the editor using ‘:sh’ command or ctrl-Z. Sometimes it is necessary to return to shell prompt to execute a UNIX command or compile our program. For this purpose, we use these commands.

Explanation: A non privileged user uses mkdir and rmdir calls for creating and removing directories respectively.

Explanation: There are two special files named /dev/null and /dev/tty which is used in UNIX for special purposes. For example, if we want to check whether the program runs successfully without seeing its output on the screen or may not want to save output in a file either. For this purpose, a special file /dev/null is used. It accepts any stream without growing in size. The second file /dev/tty is the one used for indicating one’s terminal.

Explanation: We can make the command ignorant of its source using the pipeline. Above command is also an example of the same. It will simply display the total size of those files having a .c extension in the current directory.

Explanation: bc command is used for invoking calculator on UNIX system. It comes with a wide library for performing calculations. The power of this tool can be derived from the fact, that it can perform calculations up to and above 900 digits!

Explanation: As we log on to a UNIX system, a process is immediately set up by the kernel. This process represents a UNIX command which may sh (Bourne shell), ksh (Korn shell), csh (C shell) or bash (Bash). This process remains alive until we log out when it is killed by the kernel.

Explanation: ps command is used to show some attributes of a process. This command reads through the kernel’s data structures and process tables to fetch the characteristics of a process. By default, ps command displays the processes owned by the user running the command.

Explanation: A process in UNIX is created using fork() system call. It creates an exact copy of the process that invokes it. Now there will be two processes, one parent process and one child process. The process which invokes the fork system call is called parent process and the new process created is called child process.

Explanation: To create a child shell we can use the sh command. sh is basically the command name of Bourne shell. sh is a command language interpreter that executes commands read from a command line string. To create a child shell, simply invoke sh command without any argument.

Explanation: find is one of the most powerful tools of the UNIX system. It recursively examines a directory tree to look for file matching based on some criteria and then takes some action on the selected files.

Explanation: When we concatenate or merge files, we can encounter the problem of duplicate entries creeping in. UNIX offers a special command (uniq) which can be used to handle these duplicate entries. We can also use the sort -u command for doing the same piece of work.