diff --git a/lib/awful/util.lua b/lib/awful/util.lua
index ab157171..28087899 100644
--- a/lib/awful/util.lua
+++ b/lib/awful/util.lua
@@ -22,6 +22,8 @@ local pairs = pairs
 local string = string
 local lgi = require("lgi")
 local Pango = lgi.Pango
+local Gio = lgi.Gio
+local GLib = lgi.GLib
 local capi =
 {
     awesome = awesome,
@@ -110,6 +112,94 @@ function util.spawn_with_shell(cmd, sn)
     end
 end
 
+--- Spawn a program and asynchronously capture its output line by line.
+-- @tparam string|table cmd The command.
+-- @tparam[opt] function stdout_callback Function that is called with each line of
+--              output on stdout, e.g. `stdout_callback(line)`.
+-- @tparam[opt] function stderr_callback Function that is called with each line of
+--              output on stderr, e.g. `stderr_callback(line)`.
+-- @tparam[opt] function done_callback Function to call when no more output is
+--              produced.
+-- @treturn[1] Integer the PID of the forked process.
+-- @treturn[2] string Error message.
+function util.spawn_with_line_callback(cmd, stdout_callback, stderr_callback, done_callback)
+    local have_stdout, have_stderr = stdout_callback ~= nil, stderr_callback ~= nil
+    local pid, sn_id, stdin, stdout, stderr = capi.awesome.spawn(cmd, false, false, have_stdout, have_stderr)
+    if type(pid) == "string" then
+        -- Error
+        return pid
+    end
+
+    local done_before = false
+    local function step_done()
+        if have_stdout and have_stderr and not done_before then
+            done_before = true
+            return
+        end
+        done_callback()
+    end
+    if have_stdout then
+        util.read_lines(Gio.UnixInputStream.new(stdout, true),
+                stdout_callback, step_done, true)
+    end
+    if have_stderr then
+        util.read_lines(Gio.UnixInputStream.new(stderr, true),
+                stderr_callback, step_done, true)
+    end
+    assert(stdin == nil)
+end
+
+--- Read lines from a Gio input stream
+-- @tparam Gio.InputStream input_stream The input stream to read from.
+-- @tparam function line_callback Function that is called with each line
+--         read, e.g. `line_callback(line_from_stream)`.
+-- @tparam[opt] function done_callback Function that is called when the
+--              operation finishes (e.g. due to end of file).
+-- @tparam[opt=false] boolean close Should the stream be closed after end-of-file?
+function util.read_lines(input_stream, line_callback, done_callback, close)
+    local stream = Gio.DataInputStream.new(input_stream)
+    local function done()
+        if close then
+            stream:close()
+        end
+        if done_callback then
+            xpcall(done_callback, function(err)
+                print(debug.traceback("Error while calling done_callback:"
+                    ..  tostring(err), 2))
+            end)
+        end
+    end
+    local start_read, finish_read
+    start_read = function()
+        stream:read_line_async(GLib.PRIORITY_DEFAULT, nil, finish_read)
+    end
+    finish_read = function(obj, res)
+        local line, length = obj:read_line_finish(res)
+        if type(length) ~= "number" then
+            -- Error
+            print("Error in awful.util.read_lines:", tostring(length))
+            done()
+        elseif #line ~= length then
+            -- End of file
+            done()
+        else
+            -- Read a line
+            xpcall(function()
+                -- This needs tostring() for older lgi versions which returned
+                -- "GLib.Bytes" instead of Lua strings (I guess)
+                line_callback(tostring(line))
+            end, function(err)
+                print(debug.traceback("Error while calling line_callback: "
+                    .. tostring(err), 2))
+            end)
+
+            -- Read the next line
+            start_read()
+        end
+    end
+    start_read()
+end
+
 --- Read a program output and returns its output as a string.
 -- @param cmd The command to run.
 -- @return A string with the program output, or the error if one occured.