diff --git a/pages/common/expr.md b/pages/common/expr.md
index 14912e9ee..02081aebd 100644
--- a/pages/common/expr.md
+++ b/pages/common/expr.md
@@ -1,6 +1,7 @@
 # expr
 
 > Evaluate expressions and manipulate strings.
+> More information: <https://www.gnu.org/software/coreutils/manual/html_node/expr-invocation.html>.
 
 - Get string length: