Considering the following number: 145478
I want to replace these numbers with random letters from a to z.
My attempt so far: sed -r 's/[0-9]/[a-z]/g'
It does not change the pattern to another pattern but exactly whatever I typed in the second place.
The result I got is: [a-z][a-z][a-z][a-z][a-z][a-z]
How do I make it into an actual pattern? In other words, how do I turn these numbers into random letter?