Generate a random filename in unix shell

One command, no pipe, no loop:

hexdump -n 16 -v -e '/1 "%02X"' -e '/16 "\n"' /dev/urandom

If you don't need the newline, for example when you're using it in a variable:

hexdump -n 16 -v -e '/1 "%02X"' /dev/urandom

Using "16" generates 32 hex digits.

Assuming you are on a linux, the following should work:

cat /dev/urandom | tr -cd 'a-f0-9' | head -c 32

This is only pseudo-random if your system runs low on entropy, but is (on linux) guaranteed to terminate. If you require genuinely random data, cat /dev/random instead of /dev/urandom. This change will make your code block until enough entropy is available to produce truly random output, so it might slow down your code. For most uses, the output of /dev/urandom is sufficiently random.

If you on OS X or another BSD, you need to modify it to the following:

cat /dev/urandom | env LC_CTYPE=C tr -cd 'a-f0-9' | head -c 32

why do not use unix mktemp command:

$ TMPFILE=`mktemp tmp.XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX` &&  echo $TMPFILE
tmp.MnxEsPDsNUjrzDIiPhnWZKmlAXAO8983