diff --git a/README.md b/README.md
index 4f1fad9..9680e76 100644
--- a/README.md
+++ b/README.md
@@ -53,3 +53,5 @@ _ocat_ is a CLI driver for _recorder_: it prints data stored by the _recorder_ i
 The following environment variables control _ocat_'s behaviour:
 
 * `OCAT_FORMAT` can be set to the preferred output format. If unset, JSON is used. The `--format` option overrides this setting.
+* `OCAT_USERNAME` can be set to the preferred username. The `--user` option overrides this environment variable.
+* `OCAT_DEVICE` can be set to the preferred device name. The `--device` option overrides this environment variable.
diff --git a/ocat.c b/ocat.c
index a865493..c4f4bf3 100644
--- a/ocat.c
+++ b/ocat.c
@@ -103,6 +103,13 @@ int main(int argc, char **argv)
 	time_t now, s_lo, s_hi;
 	output_type otype = JSON;
 
+	if ((p = getenv("OCAT_USERNAME")) != NULL) {
+		username = strdup(p);
+	}
+	if ((p = getenv("OCAT_DEVICE")) != NULL) {
+		device = strdup(p);
+	}
+
 	if ((p = getenv("OCAT_FORMAT")) != NULL) {
 		switch (tolower(*p)) {
 			case 'j': otype = JSON; break;