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