PHP how to count the length of each word in the text file

i need some help. how to count the length of each word in the text file using PHP.

for example. there is the test.txt. and the contain is " hello everyone, i need some help." how to output the text and then count the length of each word，like:

array

hello => 5
everyone => 8
i => 1
need  => 4
some => 4
help => 4

i just start to learn php. so please explain the detail about the code what you write.

many thanks