Generate a random UUID in bash

uuid.sh

#!/usr/bin/env bash

# Generate a pseudo UUID
uuid()
{
	local N B C='89ab'

	for (( N=0; N < 16; ++N ))
	do
		B=$(( $RANDOM%256 ))

		case $N in
			6)
				printf '4%x' $(( B%16 ))
				;;
			8)
				printf '%c%x' ${C:$RANDOM%${#C}:1} $(( B%16 ))
				;;
			3 | 5 | 7 | 9)
				printf '%02x-' $B
				;;
			*)
				printf '%02x' $B
				;;
		esac
	done

	echo
}

if [ "$BASH_SOURCE" == "$0" ]
then
	uuid
fi

The T variable can be eliminated and the for T loop can be changed to:

    case $N in
        3 | 5 | 7 | 9)
            printf '-';;
    esac

Here is the whole thing restructured using only a case block (no ifs):

uuid()
{
    local N B C='89ab'

    for (( N=0; N < 16; ++N ))
    do
        B=$(( $RANDOM%256 ))

        case $N in
            6)
                printf '4%x' $(( B%16 ))
                ;;
            8)
                printf '%c%x' ${C:$RANDOM%${#C}:1} $(( B%16 ))
                ;;
            3 | 5 | 7 | 9)
                printf '%02x-' $B
                ;;
            *)
                printf '%02x' $B
                ;;
        esac
    done

    echo
}

Note that substring expansion introduces an arithmetic context so it's not necessary to use $(()) inside it. I moved the assignment of C outside the loop. Also, the values for the modulus operations are incorrect (15 should be 16 and 255 should be 256).

Sorry for the late reaction; didn't see your comment until now.

You're right! Updated the gist to your implementation. Thanks a lot!

if you need a crypto secure version using urandom:
https://github.com/lowerpower/UUID-with-bash

Hello. fyi, this can be much much simpler. RANDOM gives 16 bits of randomness, looping over %256 is wasting so much potential. Just:

        HAS_SRANDOM=$(( (BASH_VERSINFO[0] << 16 | BASH_VERSINFO[1] << 8 | BASH_VERSINFO[2]) >= 0x050100 ))
	if ((HAS_SRANDOM)); then
		printf -v L_v "%08x%08x%08x%08x" \
			"$SRANDOM" "$(( SRANDOM & 0x3FFFFFFF | 0x40000000 ))" "$SRANDOM" "$SRANDOM"
	else
		printf -v L_v "%04x%04x%04x%04x""%04x%04x%04x%04x" \
			"$RANDOM" "$RANDOM" "$(( RANDOM & 0x3FFF | 0x4000 ))" "$RANDOM" \
			"$RANDOM" "$RANDOM" "$RANDOM" "$RANDOM"
	fi
	L_v=${L_v::8}-${L_v:8:4}-4${L_v:13:3}-${L_v:16:4}-${L_v:20}
        echo "$L_v"

Hello. fyi, this can be much much simpler. RANDOM gives 16 bits of randomness, looping over %256 is wasting so much potential. Just:

Sorry, but RANDOM is only 15 bits.