How to remember user input in a shell script? - bash

Question

I have user settings in my shell script. How can I ask user for input and remember it? In example i have in code:
ALTERNATEMEMORY="false"
I need to ask user for input (when running script in 'configure' mode):
echo "Use alternate memory?"
select yn in "true" "false"; do
case $yn in
Yes ) [permament save ALTERNATEMEMORY as "true"];;
No ) [permament save ALTERNATEMEMORY as "false"];;
esac
done
Script should ask user as above, read his input, and depending of choice set ALTERNATEMEMORY to corresponding state. Next time when running script (not configuring, just running) it should remember that setting. What should I put in these square brackets?
If I'm making mistakes when posting question, please forgive me - this is first time when I'm using stackoverflow.

Answer 1

The standard way to remember a setting from one run to the next, even after reboots, is to use a configuration file. For system-wide settings, these configuration files are usually in /etc and could be named, for example, /etc/myprog.conf. For user-specific settings, the file is usually in the home directory with a name that starts with ., such as $HOME/.myprog.conf. Pick one of those paths and create the configuration file:
echo "ALTERNATEMEMORY=false" >path/myprog.conf
Now, have the configuration section of your script update that file as desired:
echo "Use alternate memory?"
select yn in "true" "false"; do
case "$yn" in
true)
sed -i '/ALTERNATEMEMORY/ s/.*/ALTERNATEMEMORY=true/' path/myprog.conf
break
;;
false)
sed -i '/ALTERNATEMEMORY/ s/.*/ALTERNATEMEMORY=false/' path/myprog.conf
break
;;
esac
done
In the above, we used sed -i to update the file in-place. This works on linux. If you are on a BSD system (OSX), then you will need to add two quotes to that command like sed -i "" ...
Doing substitutions with an arbitrary string
If we want to set ALTERNATEMEMORY to have the value $sel where sel is a shell variable containing arbitrary characters, then we need to escape them before doing the substitution. This can be done as follows (assuming the shell is bash):
escaped_sel=$(sed 's/[&/\]/\\&/g' <<< "$sel")
sed -i "/ALTERNATEMEMORY/ s/.*/ALTERNATEMEMORY=$escaped_sel/" path/myprog.conf

Answer 2

Have a mem.conf file with the below lines
UNSET
TRUE
First line can be SET/UNSET which is to check if user has already configured and second line can be TRUE/FALSE which is to check whether to use alternate memory.
Initially the first line should be set to UNSET.
Then write the script configure.sh like below :
is_set=`head -n1 mem.conf`
if [[ $is_set == "SET" ]]
then
{
echo "Your have already configured the settings."
}
else
{
echo "Use Alternate memory?"
options=("TRUE" "FALSE" "QUIT")
select opt in "${options[#]}"
do
case $opt in
"TRUE")
echo "SET" > mem.conf
echo "TRUE" >> mem.conf
echo "Configuration Saved !!"
break;
;;
"FALSE")
echo "SET" > mem.conf
echo "FALSE" >> mem.conf
echo "Configuration Saved !!"
break;
;;
"QUIT")
echo "Seems like you have not made up your mind yet !"
echo "Please come back later."
break;
;;
*) echo "invalid option"
;;
esac
done
}
fi
echo "Configuration File : "`pwd`"/mem.conf"
The advantage here is that you could force edit mem.conf to start from scratch.