Full list of options:

ls -a list all files including hidden file starting with '.'

ls --color colored list [=always/never/auto]

ls -d list directories - with ' */'

ls -F add one char of */=>@| to enteries

ls -i list file's inode index number

ls -l list with long format - show permissions

ls -la list long format including hidden files

ls -lh list long format with readable file size

ls -ls list with long format with file size

ls -r list in reverse order

ls -R list recursively directory tree

ls -s list file size

ls -S sort by file size

ls -t sort by time & date

ls -X sort by extension name

ls shows files and directories in present working directory. (if no arguments are passed.) (It doesn't show hidden files which starts with . by default.)

user@ubuntu14:/usr$ ls
bin  games  include  lib  lib32  local  sbin  share  src

To see all files (hidden files/folders also). Use ls -a OR ls -all

user@ubuntu14:/usr$ ls -a
.  ..  bin  games  include  lib  lib32  local  sbin  share  src

To differentiate between files and folders and symbolic links and other, use ls -F OR ls --classify

user@ubuntu14:~$ ls -F
bash_profile_course  chat_apps/      Desktop/    Downloads/    foxitsoftware/   
Public/     test/    bin/    ClionProjects/  Documents/    IDE/    Music/
Pictures/  Templates/  Videos/

Here, ending characters are used to distinguish files and folders.

“/” suggest directory.

“*”suggest executables.

“@” suggest symbolic links.

To get more details about the files and directories, use ls -l

user@ubuntu14:~/example$ ls -l
total 6464

-rw-r--r-- 1 dave dave      41 Dec 24 12:19 Z.txt
drwxr-xr-x 2 user group    4096 Dec 24 12:00 a_directory
-rw-r--r-- 1 user group       6 Dec 24 12:01 a_file
lrwxrwxrwx 1 user group       6 Dec 24 12:04 a_link -> a_file
-rw-r--r-- 1 user group       6 Dec 24 12:03 a_newer_file
-rw-r----- 1 user group 6586816 Dec 24 12:07 big.zip

In this example, the total size of the contents is 6460KB.

Then there is an entry for each file/directory in alphabetical order with upper case before lower case.

The first character is the type (e.g. d - directory, l - link).

The next 9 characters show the permissions for the user, group and other.

This is followed by the number of hard links, then the owner's name and group.

The next field is the size in bytes. This can be displayed in a human friendly form by adding the -h option e.g. 6586816 is displayed as 6.3M

There then follows a timestamp (usually the modification time).

The final field is the name. Note: links also show the target of the link.