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Useful Linux Commands - III

Here are some useful linux commands...
  1. whoami - This command gives you the userid you are logged in as
  2. pwd - print working directory. When you type in this command it tells you which folder you are in and along with printing the path of the folder
  3. ls - listing. This command will list out all the files and directories under the current directory sorted alphabetically
  4. ls -F - This command lists all the files and directories with directories displayed with a trailing slash and executables have a * at the end of the executable name
  5. ls -s - lists file sizes - displays in disk blocks
  6. ls -s -h lists file sizes with human readable file sizes
  7. wc - word count displays lines, words, characters for a particular file
  8. wc -c 
  9. wc -w
  10. wc -l
  11. cat - concatenate - prints the file contents one after another
  12. sort - sorts the output 
  13. head - - gets the topN results from a file
  14. mv - move - moves a file
  15. cp - copy - copies a file
  16. rm - removes a file
  17. rmdir - removes a directory
  18. cd - change directory: users can change the directory or rather navigate 
  19. .. - special file - goes to the parent directory
  20. ls -a - show all - lists the hidden files too
  21. . - special file - gets the current directory
  22. mkdir - make directory. Creates a new directory under the current directory
  23. split - splits a given file according to the argument provided
    1. If no argument given to this command it creates a new file with the same contents in the current directory
    2. split -l 1 - splits the given file with one line of the file in a separate file thus if the given file has 3 lines after using above command there will be three separate files
  24. Permission x on a file means the file is an executable but then x on a directory means that the directory can be TRAVERSED - which means we can look at the contents of the directory
  25. chmod - change mode
    1. chmod u=rwx - user gets read, write, execute permissions
    2. chmod g=rwx - group gets read, write, execute permissions 
    3. chmod a=rwx - all get read, write, execute permissions
    4. chmod a= - all get no permissions on the file - removes all the permissions on the file
  26. You can combine two commands and run them as one using semi colon. For Ex: chmod u=r ; ls -l - this will change the user permissions for the file name given to read and then display the list of files/directories under the current directory


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