1 files changed, 63 insertions, 0 deletions
diff --git a/util/bin/magic b/util/bin/magic
new file mode 100755
index 00000000..a404c0c3
--- /dev/null
+++ b/util/bin/magic
@@ -0,0 +1,63 @@
+#! /bin/sh
+set -euf
+
+bs="# begin krebs magic <$2>"
+es="# end krebs magic <$2>"
+
+has() {
+  grep -q "^$bs$" $3 && grep -q "^$es$" $3
+}
+
+create() {
+  destroy "$@"
+  cat>>$3<<EOF
+$bs
+`cat`
+$es
+EOF
+}
+
+retrieve() {
+  sed -n "/^$bs$/,/^$es$/p" $3 | sed '1d;$d'
+}
+
+update() {
+  ! has "$@" || create "$@"
+}
+
+destroy() {
+  if has "$@"; then
+    cache="`cat $3`"
+    echo "$cache" | sed "/^$bs$/,/^$es$/d" >$3
+  fi
+}
+help() {
+cat <<EOF
+Usage: $0 FUNCTION DELIMITER_NAME FILE
+$0 creates,updates or destroys magic inside a file.
+It can be used to reliably add or remove custom lines.
+For example add own lines in /etc/rc.local to auto-load 
+scripts.
+
+FUNCTION:
+  create -- creates new magic in file, takes stdin as content in magic
+  update -- updates already existing magic with text from stdin
+  destroy -- destroys magic boundary
+  retrieve -- retrieve the content of magic and writes to stdout
+  
+Not yet implemented is the handling of magic not starting with the 
+shell comment symbol "#".
+
+EOF
+
+}
+case $1 in
+  (create) create "$@" ;;
+  (retrieve) retrieve "$@" ;;
+  (update) update "$@" ;;
+  (destroy) destroy "$@" ;;
+  (*)
+    help >&2
+    echo 'Error 1: You are made of stupid!' >&2
+    exit 23
+esac