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mqtt-grep-color

mqtt-grep-color subscribes to a MQTT topic using mosquitto_sub, adds a time stamp in front of each line, optionally greps for an expression plus colors the output. These features ease MQTT debugging on the command line quite a bit as you can see from the followinf screenshots.

sample output from mqtt-grep-color -o

Usage

  mqtt-grep-color -e <grepexpr> -h <brokerhost> -p <port> -W <no> -R -c -P -d -C <maxcount> -t <MQTT topic 1> -t <MQTT topic 2> -T <MQTT topic 3> -s -n -o

Notes

  1. Non-printable characters are removed from the mosquitto_sub output before further processing.
  2. Coloring is optional - use option -n to avoid it.
  3. Wellknown binary data (e.g. JPG, PNG) is replaced by an appropiate marker.
  4. mqtt-grep-color relies heavily on the output coloring feature of GNU grep. However, the BusyBox version of grep does not support coloring, so the script cannot color the output on BusyBox.
  5. If you happen to have a BusyBox grep that doesn't support line buffering, try to install the command stdbuf (e.g. from package "coreutils-stdbuf" on OpenWrt).
    Otherwise, ugly, bulky, delayed output might be the consequence.... (the script might warn about this)
  6. If you prefer a time stamp instead of the wallclock time, use option -s.
  7. To optimize JSON messages, use the option -o:
    This will expand abbreviated keys in Home Assistant MQTT discovery announcements and also eliminate a redundant "Time" attribute.
  8. Several options, such as -t ttt , -T ttt, -W nnn, -R, -C nnn and -c, are passed on to mosquitto_sub.
  9. Instead of live reading from mosquitto_sub, a playback file may be used with the -f with -f - for reading from stdin: mosquitto_sub -t \# -v | mqtt-grep-color -f - -o
  10. This script might be considered less useful and also would be more simply for newer versions of mosquitto_sub, since newer versions support the option -F for formatting the output, e.g. as JSON...

Examples

Example 1

# connect to the default (=localhost) broker and use standard coloring for *all* messages from the broker
mqtt-grep-color

Example 2

# connect to the default (=localhost) broker and show colored JSON messages, e.g. related to MQTT home automation
mqtt-grep-color -o

This command results in output like this:

sample output from mqtt-grep-color -o

Example 3

This command show the usage with optional parameters such as the the grep-expression, the MQTT topic and and the MQTT broker:

# follow any BBC subtitle stream, grep for lines with the's only and highlight them (dosn't make much sense but shows the capabilities)
mqtt-grep-color -e the -t "bbc/#"  -h test.mosquitto.org

This results in output like this (assuning the BBC newsfeed is still running):

Sample output from mqtt-grep-color with a grep option

Example 4

# follow BBC News 24 compacted subtitle stream for max 50 lines
mqtt-grep-color  -t "bbc/subtitles/bbc_news24/compacted"  -h test.mosquitto.org -C 50

This command results in output like this (assuning the BBC newsfeed is still running):

Another sample output from mqtt-grep-color

Additional stuff

  1. As a shortcut, if you supply "test" as the broker host, it will be interpreted as test.mosquitto.org automatically. (Same for "mqtt.eclipseprojects.io", "broker.hivemq.com", "broker.emqx.io", as well as "broker.mqttdashboard.com")
  2. In a topic: If you omit a # after a trailing /, the # will be added by default:
# So the example from above could also be entered as:
mqtt-grep-color -e e -t bbc/  -h test -C 50

Issues

  1. IMHO, the assumptions made regarding the coloring of the topic string should be based on the following reasonable best practices. However, they are not enforced yet:
    Never use a leading forward slash.
    Never use spaces in a topic.
    Use only ASCII characters, avoid non printable characters.

  2. Unfortunately, multi-line messages (containaing a line-feed char) from mosquitto_sub are hard to process, because the topic can hardly be differentiated from the message body on subsequent lines. The ugly hack introducing a unique string XXshouldbetopicXX mitigates that to a certain extent, but maybe there is less imperfect solution...

  3. If you have a firewall rule on outgoing connections such as on an OpenWrt router, a rule for the MQTT port needs to be added to /etc/config/firewall maybe followed by a reboot :

config rule 'local_client_mqtt'
        option dest_port '1883'
        option src 'local_client'
        option name 'local_client_mqtt'
        option target 'ACCEPT'
        option proto 'tcp'