diff --git a/cmd/litestream/main.go b/cmd/litestream/main.go
index c95c5f3..b830014 100644
--- a/cmd/litestream/main.go
+++ b/cmd/litestream/main.go
@@ -138,18 +138,13 @@ func (c *Config) DBConfig(path string) *DBConfig {
 }
 
 // ReadConfigFile unmarshals config from filename. Expands path if needed.
-func ReadConfigFile(filename string) (Config, error) {
+func ReadConfigFile(filename string) (_ Config, err error) {
 	config := DefaultConfig()
 
 	// Expand filename, if necessary.
-	if prefix := "~" + string(os.PathSeparator); strings.HasPrefix(filename, prefix) {
-		u, err := user.Current()
-		if err != nil {
-			return config, err
-		} else if u.HomeDir == "" {
-			return config, fmt.Errorf("home directory unset")
-		}
-		filename = filepath.Join(u.HomeDir, strings.TrimPrefix(filename, prefix))
+	filename, err = expand(filename)
+	if err != nil {
+		return config, err
 	}
 
 	// Read & deserialize configuration.
@@ -174,7 +169,12 @@ type DBConfig struct {
 }
 
 // Normalize expands paths and parses URL-specified replicas.
-func (c *DBConfig) Normalize() error {
+func (c *DBConfig) Normalize() (err error) {
+	c.Path, err = expand(c.Path)
+	if err != nil {
+		return err
+	}
+
 	for i := range c.Replicas {
 		if err := c.Replicas[i].Normalize(); err != nil {
 			return err
@@ -202,27 +202,19 @@ type ReplicaConfig struct {
 
 // Normalize expands paths and parses URL-specified replicas.
 func (c *ReplicaConfig) Normalize() error {
-	// Expand path filename, if necessary.
-	if prefix := "~" + string(os.PathSeparator); strings.HasPrefix(c.Path, prefix) {
-		u, err := user.Current()
-		if err != nil {
-			return err
-		} else if u.HomeDir == "" {
-			return fmt.Errorf("cannot expand replica path, no home directory available")
-		}
-		c.Path = filepath.Join(u.HomeDir, strings.TrimPrefix(c.Path, prefix))
-	}
-
 	// Attempt to parse as URL. Ignore if it is not a URL or if there is no scheme.
 	u, err := url.Parse(c.Path)
 	if err != nil || u.Scheme == "" {
+		if c.Type == "" || c.Type == "file" {
+			c.Path, err = expand(c.Path)
+			return err
+		}
 		return nil
 	}
 
 	switch u.Scheme {
 	case "file":
-		u.Scheme = ""
-		c.Type = u.Scheme
+		c.Type, u.Scheme = u.Scheme, ""
 		c.Path = path.Clean(u.String())
 		return nil
 
@@ -230,10 +222,6 @@ func (c *ReplicaConfig) Normalize() error {
 		c.Type = u.Scheme
 		c.Path = strings.TrimPrefix(path.Clean(u.Path), "/")
 		c.Bucket = u.Host
-		if u := u.User; u != nil {
-			c.AccessKeyID = u.Username()
-			c.SecretAccessKey, _ = u.Password()
-		}
 		return nil
 
 	default:
@@ -322,11 +310,7 @@ func newS3ReplicaFromConfig(db *litestream.DB, c *Config, dbc *DBConfig, rc *Rep
 	}
 
 	// Ensure required settings are set.
-	if accessKeyID == "" {
-		return nil, fmt.Errorf("%s: s3 access key id required", db.Path())
-	} else if secretAccessKey == "" {
-		return nil, fmt.Errorf("%s: s3 secret access key required", db.Path())
-	} else if bucket == "" {
+	if bucket == "" {
 		return nil, fmt.Errorf("%s: s3 bucket required", db.Path())
 	}
 
@@ -352,3 +336,26 @@ func newS3ReplicaFromConfig(db *litestream.DB, c *Config, dbc *DBConfig, rc *Rep
 	}
 	return r, nil
 }
+
+// expand returns an absolute path for s.
+func expand(s string) (string, error) {
+	// Just expand to absolute path if there is no home directory prefix.
+	prefix := "~" + string(os.PathSeparator)
+	if s != "~" && !strings.HasPrefix(s, prefix) {
+		return filepath.Abs(s)
+	}
+
+	// Look up home directory.
+	u, err := user.Current()
+	if err != nil {
+		return "", err
+	} else if u.HomeDir == "" {
+		return "", fmt.Errorf("cannot expand path %s, no home directory available", s)
+	}
+
+	// Return path with tilde replaced by the home directory.
+	if s == "~" {
+		return u.HomeDir, nil
+	}
+	return filepath.Join(u.HomeDir, strings.TrimPrefix(s, prefix)), nil
+}
diff --git a/cmd/litestream/replicate.go b/cmd/litestream/replicate.go
index cfd57d0..6f8e04f 100644
--- a/cmd/litestream/replicate.go
+++ b/cmd/litestream/replicate.go
@@ -36,12 +36,27 @@ func (c *ReplicateCommand) Run(ctx context.Context, args []string) (err error) {
 		return err
 	}
 
-	// Load configuration.
-	if c.ConfigPath == "" {
-		return errors.New("-config required")
+	// Load configuration or use CLI args to build db/replica.
+	var config Config
+	if fs.NArg() == 1 {
+		return fmt.Errorf("must specify at least one replica URL for %s", fs.Arg(0))
+	} else if fs.NArg() > 1 {
+		dbConfig := &DBConfig{Path: fs.Arg(0)}
+		for _, u := range fs.Args()[1:] {
+			dbConfig.Replicas = append(dbConfig.Replicas, &ReplicaConfig{Path: u})
+		}
+		config.DBs = []*DBConfig{dbConfig}
+	} else if c.ConfigPath != "" {
+		config, err = ReadConfigFile(c.ConfigPath)
+		if err != nil {
+			return err
+		}
+	} else {
+		return errors.New("-config flag or database/replica arguments required")
 	}
-	config, err := ReadConfigFile(c.ConfigPath)
-	if err != nil {
+
+	// Normalize configuration paths.
+	if err := config.Normalize(); err != nil {
 		return err
 	}
 
@@ -132,13 +147,17 @@ func (c *ReplicateCommand) Close() (err error) {
 // Usage prints the help screen to STDOUT.
 func (c *ReplicateCommand) Usage() {
 	fmt.Printf(`
-The replicate command starts a server to monitor & replicate databases 
-specified in your configuration file.
+The replicate command starts a server to monitor & replicate databases. 
+You can specify your database & replicas in a configuration file or you can
+replicate a single database file by specifying its path and its replicas in the
+command line arguments.
 
 Usage:
 
 	litestream replicate [arguments]
 
+	litestream replicate [arguments] DB_PATH REPLICA_URL [REPLICA_URL...]
+
 Arguments:
 
 	-config PATH
diff --git a/cmd/litestream/restore.go b/cmd/litestream/restore.go
index 7c2365c..68cc6a5 100644
--- a/cmd/litestream/restore.go
+++ b/cmd/litestream/restore.go
@@ -33,7 +33,7 @@ func (c *RestoreCommand) Run(ctx context.Context, args []string) (err error) {
 	if err := fs.Parse(args); err != nil {
 		return err
 	} else if fs.NArg() == 0 || fs.Arg(0) == "" {
-		return fmt.Errorf("database path required")
+		return fmt.Errorf("database path or replica URL required")
 	} else if fs.NArg() > 1 {
 		return fmt.Errorf("too many arguments")
 	}
@@ -90,7 +90,9 @@ The restore command recovers a database from a previous snapshot and WAL.
 
 Usage:
 
-	litestream restore [arguments] DB
+	litestream restore [arguments] DB_PATH
+
+	litestream restore [arguments] REPLICA_URL
 
 Arguments:
 
diff --git a/s3/s3.go b/s3/s3.go
index fc41b2f..c373f02 100644
--- a/s3/s3.go
+++ b/s3/s3.go
@@ -14,6 +14,7 @@ import (
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/aws/defaults"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/aws/aws-sdk-go/service/s3/s3manager"
@@ -647,10 +648,9 @@ func (r *Replica) Init(ctx context.Context) (err error) {
 	}
 
 	// Create new AWS session.
-	sess, err := session.NewSession(&aws.Config{
-		Credentials: credentials.NewStaticCredentials(r.AccessKeyID, r.SecretAccessKey, ""),
-		Region:      aws.String(region),
-	})
+	config := r.config()
+	config.Region = aws.String(region)
+	sess, err := session.NewSession(config)
 	if err != nil {
 		return fmt.Errorf("cannot create aws session: %w", err)
 	}
@@ -659,12 +659,21 @@ func (r *Replica) Init(ctx context.Context) (err error) {
 	return nil
 }
 
+// config returns the AWS configuration. Uses the default credential chain
+// unless a key/secret are explicitly set.
+func (r *Replica) config() *aws.Config {
+	config := defaults.Get().Config
+	if r.AccessKeyID != "" || r.SecretAccessKey != "" {
+		config.Credentials = credentials.NewStaticCredentials(r.AccessKeyID, r.SecretAccessKey, "")
+	}
+	return config
+}
+
 func (r *Replica) findBucketRegion(ctx context.Context, bucket string) (string, error) {
 	// Connect to US standard region to fetch info.
-	sess, err := session.NewSession(&aws.Config{
-		Credentials: credentials.NewStaticCredentials(r.AccessKeyID, r.SecretAccessKey, ""),
-		Region:      aws.String("us-east-1"),
-	})
+	config := r.config()
+	config.Region = aws.String("us-east-1")
+	sess, err := session.NewSession(config)
 	if err != nil {
 		return "", err
 	}