Data commit

Task/ISBN13-check-digit/UNIX-Shell/isbn13-check-digit.sh

@@ -0,0 +1,18 @@
+check_isbn13 () {
+    local i n t
+    n=${1//[^0-9]/}
+    t=0
+    for ((i=0; i<${#n}; ++i )); do
+      (( t += ${n:i:1}*(1 + ((i&1)<<1)) ))
+    done
+    (( 0 == t % 10 ))
+}
+
+for isbn in 978-1734314502 978-1734314509 978-1788399081 978-1788399083; do
+  printf '%s: ' "$isbn"
+  if check_isbn13 "$isbn"; then
+    printf '%s\n' OK
+  else
+    printf '%s\n' 'NOT OK'
+  fi
+done