diff --git a/parse-extra-vars.sh b/parse-extra-vars.sh
new file mode 100644
index 0000000..312333e
--- /dev/null
+++ b/parse-extra-vars.sh
@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Parse EXTRA_VARS into exported shell variables. Sourced by entrypoint.sh.
+
+_extra_vars_trim() {
+    local s="$1"
+    s="${s#"${s%%[![:space:]]*}"}"
+    s="${s%"${s##*[![:space:]]}"}"
+    printf '%s' "$s"
+}
+
+parse_extra_vars() {
+    [[ -z "${EXTRA_VARS:-}" ]] && return 0
+
+    local normalized line name value
+    local -a _ev_names _ev_values
+
+    normalized="${EXTRA_VARS//;/$'\n'}"
+    normalized="${normalized//,/$'\n'}"
+
+    while IFS= read -r line || [[ -n "$line" ]]; do
+        line="$(_extra_vars_trim "$line")"
+        [[ -z "$line" ]] && continue
+
+        if [[ "$line" != *"="* ]]; then
+            echo "ERROR: malformed EXTRA_VARS entry (no '='): '$line'" >&2
+            return 1
+        fi
+
+        name="${line%%=*}"
+        value="${line#*=}"
+        name="$(_extra_vars_trim "$name")"
+        value="$(_extra_vars_trim "$value")"
+
+        if [[ -z "$name" ]]; then
+            echo "ERROR: malformed EXTRA_VARS entry (empty variable name): '$line'" >&2
+            return 1
+        fi
+
+        if ! [[ "$name" =~ ^[A-Za-z_][A-Za-z0-9_]*$ ]]; then
+            echo "ERROR: malformed EXTRA_VARS entry (invalid variable name): '$name'" >&2
+            return 1
+        fi
+
+        _ev_names+=("$name")
+        _ev_values+=("$value")
+    done <<<"$normalized"
+
+    local i
+    for ((i = 0; i < ${#_ev_names[@]}; i++)); do
+        name="${_ev_names[i]}"
+        value="${_ev_values[i]}"
+        if [[ -v "$name" ]]; then
+            echo "INFO: EXTRA_VARS overwriting existing var '$name'"
+        fi
+        export "${name}=${value}"
+    done
+
+    return 0
+}