How to get octal/character form of permissions?

Question

linux

Hello!
There is a task:

Write an ls2oct function that translates a set of permissions from the character form output from the ls -l command (for example, "rwxr-xr--") to the equivalent octal value. Then write the inverse function oct2ls.

How can I write ls -l to an array or variable?
Are there any ready-made functions, or do you need to write a character value parser yourself and translate everything into octal values?
To write a reverse translation, I need permissions to be written in octal.
How can this be achieved?
Maybe some literature? In textbooks I found only a table of octal values.

Answer 1

Everything is simple here, you need to split a string of 9 characters into 3 octets
1 = rwx
2 = rx
3 = r--
Then replace and sum the characters in each octet

r = 4
w = 2
x = 1
- = 0

the output will be 754