How to view unallocated free space on a hard disk through terminal [closed]

Use GNU parted and print free command:

root@sandbox:~# parted
GNU Parted 2.3
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print free
Model: VMware Virtual disk (scsi)
Disk /dev/sda: 64.4GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type      File system  Flags
        32.3kB  1049kB  1016kB            Free Space
 1      1049kB  256MB   255MB   primary   ext2         boot
        256MB   257MB   1048kB            Free Space
 2      257MB   64.4GB  64.2GB  extended
 5      257MB   64.4GB  64.2GB  logical                lvm
        64.4GB  64.4GB  1049kB            Free Space