diff --git a/libdoc.sh b/libdoc.sh
index 31b05d9f..c055822c 100755
--- a/libdoc.sh
+++ b/libdoc.sh
@@ -57,7 +57,7 @@ fi
 
 if command -v git >/dev/null && git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   commit_id=$(git rev-parse HEAD)
-  commit_id=$(expr substr "$commit_id" $(expr length "$commit_id" - 7) 8)
+  commit_id=$(expr substr "$commit_id" 1 7)
 else
   commit_id=""
 fi
diff --git a/sitedoc.sh b/sitedoc.sh
index 0a4ad329..a1e67745 100755
--- a/sitedoc.sh
+++ b/sitedoc.sh
@@ -52,7 +52,7 @@ fi
 
 if command -v git >/dev/null && git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   commit_id=$(git rev-parse HEAD)
-  commit_id=$(expr substr "$commit_id" $(expr length "$commit_id" - 7) 8)
+  commit_id=$(expr substr "$commit_id" 1 7)
 else
   commit_id=""
 fi