Accept filters for listcon, too.

This has been implemented for listproj already, for consistency in use and implementation, the same should be available for listcon, too.

tests/t1310-listcon.sh

@@ -55,6 +55,16 @@ test_todo_session 'listcon e-mail address test' <<EOF
 @con02
 EOF
 
+cat > todo.txt <<EOF
+(B) smell the uppercase Roses +roses @outside +shared
+(C) notice the sunflowers +sunflowers @garden +shared +landscape
+stop
+EOF
+test_todo_session 'listcon with project' <<EOF
+>>> todo.sh listcon +landscape
+@garden
+EOF
+
 cat > todo.txt <<EOF
 @con01 -- Some context 1 task
 EOF

todo.sh

@@ -58,7 +58,7 @@ shorthelp()
 		    list|ls [TERM...]
 		    listall|lsa [TERM...]
 		    listaddons
-		    listcon|lsc
+		    listcon|lsc [TERM...]
 		    listfile|lf [SRC [TERM...]]
 		    listpri|lsp [PRIORITIES] [TERM...]
 		    listproj|lsprj [TERM...]
@@ -223,9 +223,10 @@ help()
 		    listaddons
 		      Lists all added and overridden actions in the actions directory.
 
-		    listcon
-		    lsc
+		    listcon [TERM...]
+		    lsc [TERM...]
 		      Lists all the task contexts that start with the @ sign in todo.txt.
+		      If TERM specified, considers only tasks that contain TERM(s).
 
 		    listfile [SRC [TERM...]]
 		    lf [SRC [TERM...]]
@@ -1135,7 +1136,8 @@ case $action in
 "listcon" | "lsc" )
     FILE=$TODO_FILE
     [ "$TODOTXT_SOURCEVAR" ] && eval "FILE=$TODOTXT_SOURCEVAR"
-    grep -ho '[^ ]*@[^ ]\+' "${FILE[@]}" | grep '^@' | sort -u
+    shift
+    eval "$(filtercommand 'cat "${FILE[@]}"' '' "$@")" | grep -o '[^ ]*@[^ ]\+' | grep '^@' | sort -u
     ;;
 
 "listproj" | "lsprj" )