You're slightly wrong in your assumptions. Block special files are things like hard drive partition, memory devices. For instance, the main partition of my hard-drive is /dev/sda1. The test's (aka [) -b flag will work for that, but it won't work for a picture file, which is considered a regular file.

$ test -b ./Pictures/NOTEBOOKS/8.jpg && echo "It's a block device" || echo "Not a block device" Not a block device $ test -b /dev/sda1 && echo "It's a block device" || echo "Not a block device" It's a block device 

Character devices are things like tty and serial consoles. For instance:

$ test -c /dev/tty1 && echo "It's a character device" || echo "Not a character dev" It's a character device 

And stat can tell you pretty much this same information, just in text form instead of exit status like test does:

$ stat --printf "%n\t%F\n" /dev/tty1 /dev/sda1 ./mytext.txt ./Pictures/NOTEBOOKS/8.jpg /dev/tty1 character special file /dev/sda1 block special file ./mytext.txt regular file ./Pictures/NOTEBOOKS/8.jpg regular file 

What you should be doing is using file command, and checking its output:

$ file ./Pictures/NOTEBOOKS/8.jpg ./Pictures/NOTEBOOKS/8.jpg: JPEG image data, JFIF standard 1.02, aspect ratio, density 100x100, segment length 16, baseline, precision 8, 750x750, frames 3 $ file /dev/sda1 /dev/sda1: block special (8/1) $ file mytext.txt mytext.txt: ASCII text 

What you also could do is filter output of hexdump of thefirst several bytes to get the file signature.

$ hexdump -C -n 16 ./Pictures/NOTEBOOKS/8.jpg 00000000 ff d8 ff e0 00 10 4a 46 49 46 00 01 02 00 00 64 |......JFIF.....d| 00000010