Difference between Unique Constraint and Unique Index

List the file size in the readable format ( B, MB, KB , GB)

List the Files with size in the readable format

 Command -    ls -h

                       h - option to display the files in the readable format like B, KB,MG, GB etc

How to list the directories alone

(1)  List directories Using ls command

      There is no direct switch / option to list the directories alone in the ls command .

      Command    =>  ls -d */     - This command is little tricky one . Refer the below explanation to understand this command   

             

      Usage          =>  -d option  to list the directory names but -d option need an argument. -d just eliminates displaying content of the directory ( ls * will display file and directories contents )  & display the directory name alone. argument here is */.    "*"  indicates the meta character which display all contents ( file, directory , link etc ) .  Forward slash (/) indicates the end of the directory .  Unix internally represents / is for directory in the end of the directory name. so */ means  any directory.  In Summary, when */ passed as argument to -d option, it picks the directories list and ignore the content of directories and display only the directory names

(2)  List the directories using echo command

 Command :  echo */  

 Usage:     Just echo *  will display all content of a directory .  */ display only directory . * indicates 0 or more characters & forward slash ( / ) indicates directory

(3) List directories using ls and grep commands

Command : ls -l | grep "^d"

Usage:      ls -l lists the directories and files. the permission field's ( 1st filed) 1st char denotes the file (f) / directory (d).  the grep command uses the regular expression carrot ( ^) which read the 1st character and then "d" denote first directory.  so ^d indicates search the first character which has 'd' and get its list.  If you want to display the files alone instead of directory, ls -l | grep "^-"

 (4) List directories using ls -F

Command: ls -F | grep "/$"

Usage:     -F option will differentiate adding forward slash (/) at the end of the directory name. grep command searches last character as "/" and list only those lines which are directories names

How to sort the files and directories size wise

   1 . Command -  Using ls command

     
     Command              ->   ls -lS     

                                              l  - Long Listing  which lists permission, links, user, group, size ,

                                                  modified/created date, file name             

                                             S  - Sort the files by Size in Descending order by default. 

                                                    Note -S is a capital letter  

     Command Usage   ->  List the files and directories file size wise ( default descending order) 

   2 . Command -  Using ls & sort commands

     Command              ->    ls -l | sort -k 5 -r   

                                             k - indicates the key and 5 indicates 5th key ( size)

                                             r - reverse in descending order size wise

                             

     Command Usage   ->  This command list the file in long format and pass the output into

                                            sort  command. Sort command takes the 5th key ( size ) and order

                                            by size in descending order.  

  

  Note                             ->   pipe symbol (|) is to pass the output of 

                                              command to next command.