Returning value from postgresql command on shell script

-A -t

-A
--no-align

Switches to unaligned output mode. (The default output mode is otherwise aligned.)

-t
--tuples-only

Turn off printing of column names and result row count footers, etc. This is equivalent to the \t command.

psql -A -t -c "SELECT 1"

Reference: http://www.postgresql.org/docs/9.0/static/app-psql.html