bee-cache: New command 'grep [grep-options] [pattern]'

Allows to grep in INVENTORY file and just print matching/non-matching lines
dependent on grep options.

Calls system grep and takes all options the system grep handles.

If no search pattern is given, undefined behavior occurs.

src/bee-cache.sh.in

@@ -71,6 +71,11 @@ function cache_update_pkg() {
     return 0
 }
 
+function cache_grep() {
+    ${BEEFLOCK} --shared ${BEECACHE_INVENTORY} \
+        grep "${@}" ${BEECACHE_INVENTORY}
+}
+
 function print_conflicts() {
     local pkg=${1}
 
@@ -239,6 +244,9 @@ cache_verify
 tmpinstall_to_filenames
 
 case "${cmd}" in
+    grep)
+        cache_grep "${@}" | cut -d ' ' -f${FIELDS}
+        ;;
     update)
         cache_update "${@}"
         ;;