bash substring of command instead of variable?

No, BASH syntax doesn't allow any kind of nesting. You can do so using external utilities like cut:

date | cut -c 1-10

Wed Jun 13

bash shell variables substring

To replace date:

$ dateWed Jun 13 14:57:38 EEST 2018

you can use printf:

$ printf "%(%a %b %d%n)T"Wed Jun 13

man strftime for more format modifiers.

bash shell variables substring

If you want the output Wed Jun 13 for today's date (which this is), then

$ date +'%a %b %e'Wed Jun 13

See the manual for date and/or for strftime on your system.

CodeHunter