Unix Operating System

Regular file, Directory file and Device files are three types of files of Unix. The regular file is also called as ordinary file. Directory file is used for directories files and diectory. The device file is used for peripheral devices and other devices operations.

• is a wild card character. It matches 0 or more occurrences of the preceding regular expression.

The $# command(shell variable) provides the number of arguments supplied to a script .

If one can replace any single character by using this command.

Man is a powerful tool that gives one complete online access to the UNIX manuals.

 sin(n) , log(n) , int() all these are awk built in functions just like in c language.

Shift + ctrl + a will generate a shell signal.

The exec() is used to execute new process in Unix.

All of the above are state of processes from run to ready like waiting for user response, waiting for disk read occurs and time slices occurs. RUNNING, READ, WAITING OR BLOCKED are states.

Cp is used to copy files and it copies the inode number to other files also.

 ^saurabh is used to search line beginning with saurabh, ^ is a wild character used for searching one instance of the string or line.

 We cannot find the file or directory name from inode. We can see the file type not file or directory name in inode attributes, so it is not a part of inode.

The awk is a multipurpose tool which has pattern scanning and processing language. It is an editor having multipurpose functionalities.

Trap is used. Trapping signals is quite easy, and the trap command has the following syntax -$ trap commands signals.

Run level 0 is used to HALT the system or system shutdown.

All users are not authorized to access tar, only admin or authorized personnel have rights to use tar command.

 The expr is to convert value in integer because unix takes by default all values in string or character , and * a strike is a wild card which has two meanings in following arithmetic formula(aritmetic formula is for product is x * y ), so back slash is used to terminate the meaning of * as wild card, because we want multiply the x and y. Therefore, the above code is correct.

The gzip, gunzip and zcat are used for compressing and expanding the files in unix. For example: gzip myflie. compress is used to compress the files in unix.

The df reports free disk space. The available space in a hard disk is determined by du command.

 Xhost is used to access remote program.

 -eq checks relation between two operands . Checks if the value of two operands are equal or not, if yes then condition becomes true. Example - [ $a -eq $b ] is not true. if a=10 and b=20.

 The startX command is used to start X server manually in unix system.

 PATH is used to search the order of the command.

The super block contains information about the entire disk and the I-node list -a list of inodes. The super block also contains an array to represent free inodes.

 <ctrl> g -  to know the line number at any instant, we use ctrl g .