根据目录中的现有文件运行linux命令

Question

In /dev/usb directory sometimes I have lp0 and sometimes lp1 . How can I change the following command to change the --name based on the content of /dev/usb ? Ie if I have lp0 in the /dev/usb directory I get:

TEST=`udevadm info --attribute-walk --name=/dev/usb/lp0 | grep "serial}==\"VL" | sed -n -e 's/^.*serial}==\"VL//p' | sed 's/\"//g'`

and if there is lp1 in /dev/usb/ directory:

TEST=`udevadm info --attribute-walk --name=/dev/usb/lp1 | grep "serial}==\"VL" | sed -n -e 's/^.*serial}==\"VL//p' | sed 's/\"//g'`

How can I save the content of /dev/usb in a variable (lp0 or lp1) and then use it in the above command?

Answer 1

You can test for readability of the lpX devices as follows:

 if test -r /dev/usb/lp0; then
    NAME=/dev/usb/lp0
 elif test -r /dev/usb/lp1; then
    NAME=/dev/usb/lp1
 else
    printf '%s\n' "could not find lp0 or lp1" >&2
    exit 1
 fi
 TEST=$(udevadm info --attribute-walk --name=$NAME ...)

Answer 2

You could write:

lp=( /dev/usb/lp? )
TEST=$( udevadm info --attribute-walk --name=${f[0]} ... )

the ? wildcard matches any 1 character.