String Substitutions

The following table describes the string substitutions that are commonly used with the GROUP, MODE, NAME, OWNER, PROGRAM, RUN, and SYMLINK keys.

String Substitution	Description
`$attr{file}` or `%s{file}`	Specifies the value of a device attribute from a file under `/sys`, such as `ENV{MATCHADDR}="$attr{address}"`.
`$devpath` or `%p`	The device path of the device in the `sysfs` file system under `/sys`, such as `RUN+="keyboard-force-release.sh $devpath common-volume-keys"`.
`$env{key}` or `%E{key}`	Specifies the value of a device property, such as `SYMLINK+="disk/by-id/md-name-$env{MD_NAME}-part%n"`.
`$kernel` or `%k`	Specifies the kernel name for the device.
`$major` or `%M`	Specifies the major number of a device, such as `IMPORT{program}="udisks-dm-export %M %m"`.
`$minor` or `%m`	Specifies the minor number of a device, such as `RUN+="$env{LVM_SBIN_PATH}/lvm pvscan --cache --major $major --minor $minor"`.
`$name`	Specifies the device file of the current device, such as `TEST=="/lib/udev/devices/$name"`.

udev expands the strings specified for RUN immediately before its program is run, which is after udev has finished processing all other rules for the device. For the other keys, udev expands the strings while it's processing the rules.