Generate Cryptographically Secure Random Passwords

#!/bin/bash

# --- Configuration ---
LENGTH=${1:-16} # Default password length is 16, or use the first argument
# Define the character set to use for the password. Avoid ambiguous chars if possible.
# Alphanumeric + common symbols
CHAR_SET='A-Za-z0-9!@#$%^&*()_+-='
# ---------------------

# Check for required commands and /dev/urandom
if ! command -v head &> /dev/null || ! command -v tr &> /dev/null || [ ! -c /dev/urandom ]; then
    echo "Error: Required commands (head, tr) or /dev/urandom not found." >&2
    echo "Please ensure core utilities are installed and /dev/urandom exists." >&2
    exit 1
fi

# Validate LENGTH is a positive integer
if ! [[ "$LENGTH" =~ ^[1-9][0-9]*$ ]]; then
    echo "Error: Invalid password length specified. Must be a positive integer." >&2
    echo "Usage: $0 [length]" >&2
    exit 1
fi

# Generate a random string using /dev/urandom
# 1. head /dev/urandom: Reads random bytes from the kernel's entropy pool.
# 2. tr -dc '$CHAR_SET': Deletes (d) all characters NOT (c) in the defined character set.
# 3. head -c "$LENGTH": Takes exactly the specified number of characters from the filtered stream.
PASSWORD=$(head /dev/urandom | tr -dc "$CHAR_SET" | head -c "$LENGTH")

if [ -z "$PASSWORD" ]; then
    echo "Error: Failed to generate password. Output was empty." >&2
    exit 1
fi

echo "Generated Password: $PASSWORD"

exit 0