Ans: Each file in UNIX has a unique number called as an inode. Using this number the file information like user, group, ownership and access mode information can be found. A files inode number can be found using the following command:
Ls –i
If the inode number is known, the following command can be used to get details of the file:
Ls –l

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Sed command in UNIX is commonly used for processing of files. Sed stands for Stream Editor which parses text files and used for making textual transformations to a file. The command specified to Sed, is applied on the file line by line.
Example:
To replace all matching occurrences of some text to another.
sed -e 's/old data/new data/g' input Filename > output Filename
Here, g is global which replaces ALL occurrence

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Process states in Linux:
Running: Process is either running or ready to run
Interruptible: a Blocked state of a process and waiting for an event or signal from another process
Uninterruptible:- a blocked state. Process waits for a hardware condition and cannot handle any signal
Stopped: Process is stopped or halted and can be restarted by some other process
Zombie: process terminated, but information is still there in the process table.

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A directory in UNIX is a special file that the kernel maintains. Only the kernel modifies the directory while the processes read them. A directory in UNIX is a association between file names and I node and hence the directory content is nothing but a list of filename and inode number pairs. When a directory is created by the kernel, two entries are made; '.' referring to the directory itself) and '..' referring to parent directory.

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Devices in UNIX are represented by files. These are special files located in the) dev directory. Hence in UNIX, every piece of hardware is a file. This device file allows us to access the hardware. For instance, the following command.
Less –f /dev/hda is not a file in the ‘real’ sense. When read, it is actually reading directly from the first physical hard disk of your machine.

  Write a shell script that requests the user’s age and then echoes it, along with some suitable comment? Ans:  Echo Hello! What\’s your age\? Read age echo $age! I\’ll be obsolete by that age! ...