simple bash script for generating random bytes

random

#!/usr/bin/env bash

read -r -d '' usage <<EOF
Usage:
    random [options] bytes
    random -h|--help

Generate random bytes from /dev/random.

Options:
    -h, --help
        print help
EOF

error() {
    printf >&2 "Error: %s\n\n%s\n" "$*" "$usage"
}

main() {
    if (($# != 1)); then
        error "Incorrect number of argument"
    elif [[ $1 =~ (-h|--help) ]]; then
        printf "%s\n" "$usage"
    elif [[ $1 =~ ^[0-9]+$ ]]; then
        local bytes=""
        while ((${#bytes} < $1)); do
            bytes+=$(head --bytes $(($1 - ${#bytes})) /dev/random |
                tr --complement --delete 'a-zA-Z0-9~!@#$%^&*_-')
        done
        printf "%s" "${bytes:0:$1}"
    else
        error "'bytes' must be a non-negative integral value"
    fi
}

main "$@"

PSA

Not cryptographically secure. But if I had to tell you that, then you're most certainly in the wrong place