diff --git a/backup-if-change.sh b/backup-if-change.sh
new file mode 100644
index 0000000..32a6138
--- /dev/null
+++ b/backup-if-change.sh
@@ -0,0 +1,99 @@
+#!/usr/bin/env bash
+
+set -o errexit
+set -o errtrace
+set -o nounset
+
+function trap_err()
+{
+    echo Exiting because error occurred in script.
+}
+trap trap_err ERR
+
+
+HASH_TOOL="sha256sum"
+INTERNEL=32
+TARGET_DIR=""
+FILE=""
+
+
+function show_usage()
+{
+    echo "$0 usage:"
+    echo "  --target-dir    Directory to store the backup files"
+    echo "  --file          The file to monitor"
+    echo "  --hash-tool     Tools to calculate hash of file, default sha256sum"
+    echo "  --internel      Seconds between checking file, default 32s"
+}
+
+function my_log()
+{
+    echo "$(date --iso-8601=ns) -- $*"
+}
+
+function backup_the_file()
+{
+    local the_file=$1
+    local target="${the_file}_$(date --iso-8601=seconds --reference $the_file)"
+    my_log "backuping the file to $target"
+    
+    if [ -f "$TARGET_DIR/$target" ]
+    then
+        my_log "$target already exists, skipped."
+    else
+        cp --no-target-directory $the_file $TARGET_DIR/$target
+    fi
+}
+
+
+function main()
+{
+    while [ "$#" -gt 1 ]
+    do
+        case "$1" in
+            "--target-dir")
+                TARGET_DIR=$2
+                shift
+                ;;
+            "--file")
+                FILE=$2
+                shift
+                ;;
+            "--hash-tool")
+                HASH_TOOL=$2
+                shift
+                ;;
+            "--internel")
+                INTERNEL=$2
+                shift
+                ;;
+            *)
+                echo unknown option: $1
+                show_usage
+                exit 1
+                ;;
+        esac
+        shift
+    done
+
+    if [ -z "$FILE" -o -z "$TARGET_DIR" ]
+    then
+        echo "option(s) --file or --target-dir is unspecified."
+        exit 1
+    fi
+    hash_prev=""
+    while [ "true" ]
+    do
+        hash_curr=$(eval "$HASH_TOOL $FILE")
+        if [ "$hash_prev" != "$hash_curr" ]
+        then
+            my_log "the hash now: $hash_curr"
+            backup_the_file $FILE
+            hash_prev=$hash_curr
+        fi
+
+        sleep "$INTERNEL"
+    done
+}
+
+main "$@"