How to set 4 space tab in bash

That’s not a property of your shell (or php or cat). It’s your terminal that manages the output.

Use the tabs command to change the behavior:

$ tabs 4

$ echo -e "a\tb"      
a   b
$ tabs 12

$ echo -e "a\tb" 
a           b

(tabs is specified in POSIX, and output above is “faked”: it’s still a tab character between the two letters.)