Noob needs brief help with shell scripting. *shows shame*

[AreonEpta]

My script doesn't work. I'm trying to find out why by reading tutes and FAQs but to no avail. I'm trying to make it so that I can turn on and off power saves tunes when I want to. The script keeps returning errors.

My shell script, saved as "powermanage" and then chmod 755'd:

#/bin/bash
clear
if /sys/devices/system/cpu/sched_mc_power_savings=0 ; then
echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
elif /sys/devices/system/cpu/sched_mc_power_savings=1
echo 0 > /sys/devices/system/cpu/sched_mc_power_savings
fiMy error:

~/Desktop$ ./powermanage
./powermanage: line 5: syntax error near unexpected token `else'
./powermanage: line 5: `else'
HALP!

[mcai8sh4]

Not sure if this helps, but I'm sure someone in the know will sort this for you.
Have you tried adding " ; then" to the end of you 'elif' line?

eg : elif /sys/devices/system/cpu/sched_mc_power_savings=1; then

Regards

Steve

edit : this has helped me alot in the past could of weeks
http://www.tldp.org/LDP/abs/abs-guide.pdf

[AreonEpta]

That fixed that. Now I'm getting:

~/Desktop$ ./powermanage
./powermanage: line 3: /sys/devices/system/cpu/sched_mc_power_savings=0: No such file or directory
./powermanage: line 5: /sys/devices/system/cpu/sched_mc_power_savings=1: No such file or directory

[mcai8sh4]

when you change dir to "/sys/devices/system/cpu/" are those files there?
Surely having a filename with '=0' or '=1' at the end is wrong.

I'm only guessing but I think your confused as to what your script is trying to do.
The way I see it you are writing '0' into a file (with '=0' at the end of the file name). For this to work the file would have to exist. But It sounds wrong to me.

Sorry If I've misunderstood, but I don't really know what your trying to do.

edit : have a look at this - might assist you...
http://ubuntuforums.org/showthread.php?t=908264

-s

[AreonEpta]

I'm trying to check if the file = 1, if so then write 0 into the file. If not then write 1 into the file.

[mcai8sh4]

ok I see what you're trying to do.
As mentioned in my edit http://ubuntuforums.org/showthread.php?t=908264 might point you in the right direction.

I not great with scripts, I usually have to rewrite mine a few times before I get them right, but if I can help you, I may learn somthing as well :)

For your If statement I would imagine youd have to compare the contents of the file - something along the lines of


if [ "$(cat /sys/devices/system/cpu/sched_mc_power_savings" = "0" ]; then

the speech marks may be wrong, I always confuse between handling number or strings, but the line above compares the CONTENTS of the file with the value (char?) 0

[mssever]

For your If statement I would imagine youd have to compare the contents of the file - something along the lines ofCorrection:


if [[ "$(cat /sys/devices/system/cpu/sched_mc_power_savings)" = 0 ]]; then

[AreonEpta]

Thank you both so much. It's working great now. I really appreciate the help. I'd love it if you could point me towards a place where I could learn to understand some of the syntax you both used. I've yet to check out that link in your edit, but I'm about to; that may be just what I need.

THANKS AGAIN!

[mssever]

I'd love it if you could point me towards a place where I could learn to understand some of the syntax you both used.
http://tldp.org/LDP/abs/html/

Don't let the name fool you. It includes the basics, as well as the advanced stuff.

[AreonEpta]

Thanks mssever. That'll do it.

[AreonEpta]

Okay. So more troubles...


#/bin/bash
if [[ "$(cat /sys/devices/system/cpu/sched_mc_power_savings)" = 0 ]]; then
sudo echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
echo "***Powersave Mode active***"
elif [[ "$(cat /sys/devices/system/cpu/sched_mc_power_savings)" = 1 ]]; then
sudo echo 0 > /sys/devices/system/cpu/sched_mc_power_savings
echo "***Performance Mode active***"
fireturns...


./powermanage: line 3: /sys/devices/system/cpu/sched_mc_power_savings: Permission denied


Also, when I go to enter it in Terminal, I get a bash error...

bash: /sys/devices/system/cpu/sched_mc_power_savings: Permission denied

And then when I go to open it in Text Editor I get...

Could not open the file /sys/devices/system/cpu/sched_mc_power_savings.
Unexpected error: No such device

Any ideas?

[mcai8sh4]

glad you're moving on (and thanks to mssever for correcting me - I'm always getting my syntax wrong).

Not sure on the best way to give you permission (run the script as root? maybe)
If I think of anything I'll let yuo know.

[AreonEpta]

glad you're moving on (and thanks to mssever for correcting me - I'm always getting my syntax wrong).

Not sure on the best way to give you permission (run the script as root? maybe)
If I think of anything I'll let yuo know.

So, then...?

~$ sudo ./powermanage

Like that? I'm at work now, and obviously enough, we use winders here. I'll check and see if that does it when I get home.

[mssever]

#/bin/bash
if [[ "$(cat /sys/devices/system/cpu/sched_mc_power_savings)" = 0 ]]; then
sudo echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
echo "***Powersave Mode active***"
elif [[ "$(cat /sys/devices/system/cpu/sched_mc_power_savings)" = 1 ]]; then
sudo echo 0 > /sys/devices/system/cpu/sched_mc_power_savings
echo "***Performance Mode active***"
fireturns...


./powermanage: line 3: /sys/devices/system/cpu/sched_mc_power_savings: Permission denied

A quirk of sudo is that it only applies to a single process, so redirection loses its privileges. So, something like this would work:
echo 1 | sudo tee /sys/devices/system/cpu/sched_mc_power_savings

So, then...?

~$ sudo ./powermanageLike that?
That will work as well. Of course, it'll mean that your entire script will run as root (and you won't need to use sudo at all within the script).

As to which approach is better, it's a bit of a tossup. On the one hand, it's best to have as little as possible running as root, which would favor the first solution. On the other hand, calling the entire script with sudo serves to alert the user that the script uses root privileges, which wouldn't always happen otherwise (for example, if sudo didn't need to prompt for a password). So you'll have to decide which you think is best.

[AreonEpta]

Thanks. I'll give that a try when I get off work.