What is the meaning for $! in shell or shell scripting? I am trying to understand a script which has the something like the following.
local@usr> a=1
local@usr> echo $a
1
local@usr> echo $!a
a
It is printing the variable back. Is it all for that? What are the other $x options we have? Few I know are $$, $*, $?. If anyone can point me to a good source, it will be helpful. BTW, This is in Sun OS 5.8, KSH.
From the ksh man page on my system:
${!vname}
Expands to the name of the variable referred to by vname. This
will be vname except when vname is a name reference.
The various $… variables are described in Bash manual. According to the manual $! expands to the PID of the last process launched in background. See:
$ echo "Foo"
Foo
$ echo $!
$ true&
[1] 67064
$ echo $!
67064
[1]+ Done true
In ksh it seems to do the same.
It gives the Process id of last backgroundjob or background function Please go through this link below
http://www.well.ox.ac.uk/~johnb/comp/unix/ksh.html#specvar
! is a reference operator in unix, though it is not called with that name.
It always refers to a mother process. Try typing :! in vi, it takes you to command prompt and you can execute commands as usual until exit command.
! in SQLPLUS also executes the command from the command prompt. try this in sqlplus
SQL> !ls --- this gives the list of files inthe current dir.
$! - obviously gives the process id of the current/latest process.