su (switching to other user)

bjagadeesh · #1 (**permalink**) 05-20-2008

Hi,

what is the use of the double quotes and !! in the following code segment:

su - user1 << ""!! > /dev/null 2>&1
echo "welcome user1"
EOF
!!

also what is the difference between below:

su - user1 << ""!! > /dev/null 2>&1 and
su - $USER << ""!!!> /dev/null 2>&1.

Note: $USER = user2

Jagadeesh.

jim mcnamara · #2 (**permalink**) 05-20-2008

The !! marks the boundaries of a here document. Why the EOF is there I have no idea.
the "" (empty string ) forces the shell to "see" the !! probably because of an older shell.
It will work in a modern shell, like ksh, without the "". Either way works. The "" seems just to add confusion for me.

You can use !!! or any other nonsense (nonsense to the shell) combination of letters to set up a here doc. The only requirement is that they be indentical. like EEE and EEE

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