Bash script string comparison error, can't figure out

Question

I fixed the code below so it works:

#!/bin/bash
out="$(cat /proc/acpi/bbswitch)"
if [[ "$out" == *OFF* ]];
then
    tee /proc/acpi/bbswitch <<<ON
    echo "Nvidia card activated."
else
    tee /proc/acpi/bbswitch <<<OFF
    echo "Nvidia card disabled."
fi

This is made for activating or disabling my optimus card. I get an error on line 4:

./.bb: line 4: [0000:01:00.0 OFF: command not found
OFF
Nvidia card disabled.

I can read from it that it tries to execute the $out variable. Why?

You've made several changes to the question. Does the error still occur? — glenn jackman
– glenn jackman, Commented Nov 12, 2012 at 22:16

sampson-chen · Accepted Answer · 2012-11-12 21:22:54Z

4

You need to ensure that there is at least 1 space between the brackets [ / ] and the actual variables; i.e.: change your code from

if ["$out" == "$is"];

to:

if [ "$out" == "$is" ];

And it should work.

The reason is that [ is actually the "test" command in bash. Try on your prompt:

which [

and you should see something like:

/usr/bin/[

Also, man [ to read more about syntax

(Note, since arguments are delimited by spaces, there needs to be a space between your 2nd variable and ] as well. Test uses ] as the terminating sentinel)

edited Nov 12, 2012 at 21:22

answered Nov 12, 2012 at 21:16

sampson-chen

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3 Comments

Tristan Šneider Over a year ago

hmm.. I fixed it now, but there is a problem with the if statement. It never executes the ON part, only the OFF part.

rg88 Over a year ago

I tried your command, Tristan, with sampson-chen's change and it works. Perhaps you are not getting the value you expect for one of your variables? Try adding this, set -x, right below your #!/bin/bash You can debug the output this way.

Tristan Šneider Over a year ago

[[ 0000:01:00.0 OFF == \O\F\F ]] what is that supposed to mean, the \O\F\F

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