My OS is AIX5.1, ksh and DB2 UDB 8.1 for AIX, the following is my screen capture. Why the second echo command print a NULL string?

db2 "select count(*) from spe.reexecutepoint"

1
-----------
2

1 record(s) selected.

$ unset a
$ db2 "select count(*) from spe.reexecutepoint" | sed -n '4s/[[:blank:]]//gp' | read a
$ echo $a
2
$ unset a
$ a=`db2 "select count(*) from spe.reexecutepoint" | sed -n '4s/[[:blank:]]//gp'`
$ echo $a

$ unset a
$ a=`db2 connect to dl>/dev/null;db2 "select count(*) from spe.reexecutepoint" | sed -n '4s/[[:blank:]]//gp'`
$ echo $a
2
$

when you use `command` you are forking a new shell. When you fork a new shell, you need a db2 connect in the new shell.

This is the same as:

db2 connect ...
db2 "select count (*) ...." this command will return a result

now if you type:
sh <return> # start a new shell
db2 "select count(*) ...."

you will get:
SQL1024N A database connection does not exists.

if you type "exit" and get back to previous shell and
db2 "select count(*) ...."

you will get a result.

Thank you for your replay, I know!