running parts of shell script in background - sql

Question

I have a shell script which asks for user input and depending on the input opens db connection using sqlplus and run some sql querys like drop table /create table/select/update. Is it possible that the sql part be run as background job,so that even if i lose vpn connectivity to the network,all the sql queries gets executed.
Also ,when the sql parts gets completed and user is prompted with another input the shell script comes to foreground and after getting the input again goes to background?
I have found some questions which tell us how to run the script in background,but i want to run ONLY some parts of the same script in background if possible(and come to foreground for user input).Though i can make multiple scripts too handle it(dividing the scripts in parts which needs to be called in background and calling them though another script),i would rather do it in a single script if possible.

Answer 1

You can break your main script up into functions / smaller scripts to achieve the desired behavior of a mix of background processes and foreground processes.
For example, in your main script:
#!/bin/sh
echo "Starting script..."
# do so more stuff here, maybe ask user for input
./run_background_process_1 &
# ask the user for some more input
./run_background_process_2 &
...
Use the & symbol at the end of script calls to denote that they should be run in the background.
(Updated) If you'd like to keep everything in 1 script, use functions to break up / encapsulate the parts of logic that you would like to run in the background. Call these functions by suffixing the call with &, same as above.
You can try the following example to see that it works:
#!/bin/sh
hello() {
condition="yes"
while [[ $condition== "yes" ]]
do
echo "."
sleep 1
done
}
# Script main starts here
echo "Start"
hello &
echo "Finish"
Remove the & after hello and you'll see that it behaves differently.
There are tools which allow you to keep scripts running despite loss of connection. For example, check out http://www.gnu.org/software/screen/ - one of its features is Programs continue to run when their window is currently not visible and even when the whole screen session is detached from the users terminal.

Answer 2

After search on internet i found out i can use three methods to make the script background :
1) using bg: How do I put an already-running process under nohup? .but unfortunately ,this didnt worked for me in ksh shell.
2) using coprocesses
3) using nohup
I decided to go with nohup as it was easier to implement. The sqlplus part which needed to be run in background ,i made another script of it and called it from the main script using nohup
nohup script-name.ksh ${parameter1} ${paramter2} &
This worked for me.