eval - construct command by concatenating arguments

1) foo=10 x=foo
2) y='$'$x
3) echo $y
4) $foo
5) eval y='$'$x
6) echo $y
7) 10

eval [arg ...]
    The  args  are read and concatenated together into a single com-
    mand.  This command is then read and executed by the shell,  and
    its  exit status is returned as the value of eval.  If there are
    no args, or only null arguments, eval returns 0.

andcoz@...:~> $( echo VAR=value )
bash: VAR=value: command not found

andcoz@...:~> eval $( echo VAR=value )
andcoz@...:~> echo $VAR
value

eval [arg ...]
    The args are read and concatenated together into a single command.
    This command is then  read  and executed by the shell, and its exit
    status is returned as the value of eval.  If there are no args, or only
    null arguments, eval returns 0

eval: eval [arg ...]
    Execute arguments as a shell command.

    Combine ARGs into a single string, use the result as input to the shell,
    and execute the resulting commands.

    Exit Status:
    Returns exit status of command or success if command is null.

/home/user1 > a="ls | more"
/home/user1 > $a
bash: command not found: ls | more
/home/user1 > # Above command didn't work as ls tried to list file with name pipe (|) and more. But these files are not there
/home/user1 > eval $a
file.txt
mailids
remote_cmd.sh
sample.txt
tmp
/home/user1 >