Question

I read this line of script in book [linux device drivers]. What does it do?

major=$(awk "\\$2=  =\"$module\" {print \\$1}" /proc/devices)

as in context:

#!/bin/sh
module="scull"   
device="scull"  
mode="664"

# invoke insmod with all arguments we got  
# and use a pathname, as newer modutils don't look in . by default

/sbin/insmod ./$module.ko $* || exit 1


# remove stale nodes  
rm -f /dev/${device}[0-3]   

major=$(awk "\\$2=  =\"$module\" {print \\$1}" /proc/devices)

mknod /dev/${device}0 c $major 0
....

Answer 1

I read this too but that line was not working for me. I had to modify it to

major=$(awk "\$2 == \"$module\" {print \$1}" /proc/devices)

The first part \$2 == \"$module\" is the pattern. When this is satisfied, that is, the second column is equal to “scull”, the command print \$1 is executed which prints the first column. This value is stored in the variable major.
The $ needs to be escaped as they need to be passed as it is to awk.