du

du 
    -a    # display entery for each file.
    -c    # display a grand total.
    -d    # depth
    -s    # display entry for ea file specified. = -d 0
    -h    # human readable (gb, mg, kb)
    -H    # only symbolic links are followed in cli.
    -L    # all symbolic links are followed.
    -P    # no symbolic links followed (default).
    
# highly used example
du -sch

# list all jpg files in any subdir of current dir
du -ch */*.jpg