postgresql: fill up or truncate the string to length

pad.sql

rpad(string text, length int [, fill text]) 
fill is space by default

select rpad('hello', 10, 'w') -- hellowwwww
select lpad('hello', 10, 'p') -- ppppphello
select lpad('hello', 10)      -- '     hello'
select rpad('hello', 4)       -- hell