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 occurrences. 

Ans: 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.

Ans:

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.

Ans:

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.