New to bash scripting; making script to change laptop CPU governor

Question

I've got an old laptop and I like to be able to change the governor between performance and ondemand depending on whether or not I've got the laptop plugged in. I'd really like to be able to do this from a shortcut on the desktop, so I decided to try making a bash script that used Zenity dialogs to accomplish this.
I think it turned out pretty much how I'd like, however the error handling on getting the root password authenticated is pretty broken. I'm not sure how exactly I should go about it.. I think that the long timeout that occurs when you enter a wrong password for su is causing problems. Is there a better way of doing this? I don't use sudo, and I'd really prefer to avoid it and stick to using su if at all possible.
#!/bin/bash
#This script will supply a Zenity dialog with the option to change the laptop's governor.
#It will use a Zenity dialog to acquire the root password from user for autorization to change the governor.
#Set up some variables we will use.
optionPerformance="FALSE"
optionOndemand="FALSE"
#Read the current state of the governor.
currentGovernor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
#Change the variables we previously set up to reflect current state of governor. This will be used to determine which option is pre-selected in the Zenity dialog we will create.
if [ $currentGovernor = 'performance' ]
then optionPerformance="TRUE"
fi
if [ $currentGovernor = 'ondemand' ]
then opitonOndemand="TRUE"
fi
#Set up Zenity dialog which allows user to select the governor they want active. The currently active governor will be selected by default.
#User's input will go to the wantedGovernor variable for future use.
wantedGovernor=$(zenity --list --text "Select which governor you want to make active:" --radiolist --column "" --column "Options" $optionPerformance "performance" $optionOndemand "ondemand")
#Check to see if user clicked Cancel button.
if [ $? = 1 ]
then exit 0
fi
#Did user select the already active profile? If so, simply report that and exit.
if [ $wantedGovernor = $currentGovernor ]
then
newGovernor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
zenity --info --text "Governor is already set to $newGovernor.\n\nNo changes were made."
exit 0
fi
#Now that we know what the user wants, let's do it.
#We will use cpupower to change the governor. This will require root privileges, so we will use Zenity to get the root password from user and pipe it into su. (Is this the best way?)
zenity --title "Password for root:" --password | su -c "cpupower frequency-set -g $wantedGovernor"
#Check to see if user clicked Cancel button.
if [ ${PIPESTATUS[0]} = 1 ]
then exit 0
fi
#Check to see if user entered incorrect root password.
if [ ${PIPESTATUS[1]} = 1 ]
then
zenity --error --text "Incorrect root password.";
exit 1
fi
#Now that we've made the change, let's check the current state of the governor again so that we can report it to the user and they can verify success.
newGovernor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
zenity --info --text "Governor is now set to $newGovernor."
Last edited by gilmoreja (2015-01-26 21:49:19)

Answer 1

Thanks for the advice, Awebb. I looked into gksu but I didn't like how it offered to save the root password in gnome-keyring. I found an alternative, ktsuss, and decided to go with that instead.
I'll post the finished script here, for anyone who is ever interested in such a thing:
#!/bin/bash
#This script will supply a Zenity dialog with the option to change the laptop's governor.
#It will use a Zenity dialog to acquire the root password from user for autorization to change the governor.
#Set up some variables we will use.
optionPerformance="FALSE"
optionOndemand="FALSE"
#Read the current state of the governor.
currentGovernor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
#Change the variables we previously set up to reflect current state of governor. This will be used to determine which option is pre-selected in the Zenity dialog we will create.
if [ $currentGovernor = 'performance' ]
then
optionPerformance="TRUE"
fi
if [ $currentGovernor = 'ondemand' ]
then optionOndemand="TRUE"
fi
#Set up Zenity dialog which allows user to select the governor they want active. The currently active governor will be selected by default.
#User's input will go to the wantedGovernor variable for future use.
wantedGovernor=$(zenity --list --text "Select which governor you want to make active:" --radiolist --column "" --column "Options" $optionPerformance "performance" $optionOndemand "ondemand")
#Check to see if user clicked Cancel button.
if [ $? = 1 ]
then exit 0
fi
#Did user select the already active profile? If so, simply report that and exit.
if [ $wantedGovernor = $currentGovernor ]
then
newGovernor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
zenity --info --text "Governor is already set to $newGovernor.\n\nNo changes were made."
exit 0
fi
#Now that we know what the user wants, let's do it.
#We will use cpupower to change the governor. This will require root privileges, so we will use ktsuss to get that.
ktsuss cpupower frequency-set -g $wantedGovernor
#Now that we've made the change, let's check the current state of the governor again so that we can report it to the user and they can verify success.
newGovernor=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
zenity --info --text "Governor is now set to $newGovernor."