if-else to check whether sd card or usb disk.?

Question

How can I set this up so that it itself checks if there is an sd or usb, so it makes a backup depending on whether I have an sd card or usb disk attached?

dd if=/dev/mmcblk0 of=${BACKUP_PATH}/${HOSTNAME}${ARCHITECTURE}bits-${BACKUP_DATO}.img bs=1MB status=progress
echo "Backup Image from SD-Kort"
dd if=/dev/sda of=${BACKUP_PATH}/${HOSTNAME}${ARCHITECTURE}bits-${BACKUP_DATO}.img bs=1MB status=progress
echo "Backup Image from USB"

I suggest you man bash and test to see if the file exists. — joan, Jun 01 '22 at 14:46
Ugh! Why use dd with all of its flaws as a backup solution? Try image-backup instead - the "how to" is in another answer here on SE — Seamus, Jun 01 '22 at 21:08

Bodo · Accepted Answer · 2022-06-01T16:40:49.923

1

If exactly one of /dev/mmcblk0 and /dev/sda exists and shall be saved, you could use something like

if [ -e /dev/mmcblk0 ]
then
    dd if=/dev/mmcblk0 of=${BACKUP_PATH}/${HOSTNAME}${ARCHITECTURE}bits-${BACKUP_DATO}.img bs=1MB status=progress
    echo "Backup Image from SD-Kort"
else
    dd if=/dev/sda of=${BACKUP_PATH}/${HOSTNAME}${ARCHITECTURE}bits-${BACKUP_DATO}.img bs=1MB status=progress
    echo "Backup Image from USB"
fi

or

if [ -b /dev/mmcblk0 ]
...

-e checks the existence of any file system object, -b checks for the existence of a block device, -f checks for a regular file (which does not match here).

Depending on your needs you could also check what device is mounted as /, e.g. by parsing the output of mount.

edited Jun 01 '22 at 16:40

answered Jun 01 '22 at 15:06

Bodo

253
1
7

@Bobo
if [ -f /dev/mmcblk0 ]
then

i get it to work with :

if [ -b /dev/mmcblk0 ]; then

what is the difference. ?
– Assassins Jun 01 '22 at 15:25
@Assassins You are right. It must be -e or -b, not -f; see updated answer. – Bodo Jun 01 '22 at 16:41
@Bobo Thanks for the answer, you help and time :-) – Assassins Jun 01 '22 at 19:09

if-else to check whether sd card or usb disk.?

1 Answers1