handle non-zero exit codes, newlines, empty strings in stdout

README.md

@@ -319,6 +319,19 @@ The options for the `time` segment are:
 
 - `format`: Format string as used by strftime function, e.g. `%H:%M`.
 
+The options for the `stdout` segment are:
+- `command`: A list of arguments determining the command to run.
+- `fg_color`: The foreground color of the segment when the command succeeded.
+- `bg_color`: The background color of the segment when the command succeeded.
+- `error_fg_color`: The foreground color of the segment when the command
+  returned a non-zero exit code.
+- `error_bg_color`: The background color of the segment when the command
+  returned a non-zero exit code.
+- `allow_error`: If true, the segment will be shown when the command returns a
+  non-zero exit code.
+- `hide_empty`: If true, the segment will not be shown when the command outputs
+  an empty string or only whitespace.
+
 ### Contributing new types of segments
 
 The `powerline_shell/segments` directory contains python scripts which are

powerline_shell/segments/stdout.py

@@ -1,17 +1,50 @@
 import subprocess
-from ..utils import ThreadedSegment
+from ..utils import ThreadedSegment, warn
 
 
 class Segment(ThreadedSegment):
     def run(self):
-        cmd = self.segment_def["command"]
-        self.output = subprocess.check_output(cmd).decode("utf-8").strip()
-        # TODO handle OSError
-        # TODO handle no command defined or malformed
+        cmd = self.segment_def.get("command", [])
+
+        if len(cmd) == 0:
+            warn("no command specified")
+            self.output = None
+            return
+
+        try:
+            self.output = subprocess.check_output(cmd).decode("utf-8").strip()
+            self.success = True
+        except subprocess.CalledProcessError as ex:
+            if self.segment_def.get("allow_error", True):
+                self.output = ex.output.decode("utf-8").strip()
+            else:
+                self.output = None
+
+            self.success = False
+
+        # TODO handle malformed command
 
     def add_to_powerline(self):
         self.join()
-        self.powerline.append(
-            " %s " % self.output,
-            self.segment_def.get("fg_color", self.powerline.theme.PATH_FG),
-            self.segment_def.get("bg_color", self.powerline.theme.PATH_BG))
+
+        if self.output is None:
+            return
+
+        if self.success:
+            fg_color = self.segment_def.get("fg_color", self.powerline.theme.PATH_FG)
+            bg_color = self.segment_def.get("bg_color", self.powerline.theme.PATH_BG)
+        else:
+            fg_color = self.segment_def.get("error_fg_color", self.powerline.theme.CMD_FAILED_FG)
+            bg_color = self.segment_def.get("error_bg_color", self.powerline.theme.CMD_FAILED_BG)
+
+        for i, line in enumerate(self.output.split("\n")):
+            line = line.strip()
+            if len(line) == 0 and self.segment_def.get("hide_empty", False):
+                continue
+
+            if i > 0:
+                self.powerline.append("\n",
+                    self.powerline.theme.RESET,
+                    self.powerline.theme.RESET,
+                    separator="")
+            self.powerline.append(" %s " % line, fg_color, bg_color)