Alfred 3 Tip: Use stderr to output to the debug console

[sxalexander]

I love Alfred but I struggled at first to troubleshoot my workflow scripts due to difficulty finding a way to debug.  I've seen posts mentioning writing logs to an external file but that seemed hack-y, especially since Alfred includes a debug console.  If you'd like to use the console to debug your scripts, I found the following very useful.  It would be great if there were a mention of this in the docs:

 

To show script output in the debug console, print (or echo or put, etc) the output to stderr instead of stdout.

 

In a Bash script:

>&2 echo "Log this output to the console"

 

In a Python script:

import sys

sys.stderr.write("Log this to the console")

 

For other languages, look for an equivalent method that allows you to log to stderr.

Edited June 27, 2016 by sxalexander

[deanishe]

If you're going to use sys.stderr.write() in Python, don't forget to add the trailing newline: 

sys.stderr.write('Message\n')

 
For simple scripts, I normally use this log() function: 

# Needed to use print this way
from __future__ import print_function
 
def log(s, *args):
    if args:
        s = s % args
    print(s, file=sys.stderr)
 
# Usage 
log('var1=%r, var2=%r', var1, var2)

Edited June 27, 2016 by deanishe

[nk9]

Sorry to necropost, but I just ran into this and wanted to provide another solution. I was getting "JSON error: JSON text did not start with array or object and option to allow fragments not set." The problem was of course that I was printing debugging strings to stdout before my JSON. In modern Python, the solution is very clean:

import logging
import json

out = { "items": [{"title": "Result!"}]}
logging.warning(f"{out=}")

json.dumps(out)

 

Prints:

WARNING:root:out={"items": [{"title": "Result!"}]}