Questions Nobody Asked..

Python-style Logging in Bash

08 Jan 2020

One of the great sins in programming is trying to write code in one language like code from another language.

Having said that, I’m a shell scripting newbie. So when I had cause to write some bash, I found myself reaching for some python ‘home comforts’.

Okay, so what I actually did wasn’t so bad

function log() {
    echo "log: $@" >&2
}

I think this is a fairly common approach to ‘logging’ in bash.

But around the same time, I was reading about arrays in bash, and that gave me an idea for how you could implement python-style logging, with variable logging levels.

Code

#!/usr/bin/env bash

_LEVELS=(DEBUG INFO WARNING ERROR CRITICAL)

export DEBUG=10
export INFO=20
export WARNING=30
export ERROR=40
export CRITICAL=50


function log() {
    # Write a message to logging at the given level
    #
    # Usage: log <level> <message>

    local effective=${LOGLEVEL:-$WARNING};

    local level=$1;
    local levelname=${_LEVELS[$((level/10-1))]};

    shift;

    if [[ $level -ge $effective ]]; then
        printf "%s:%s: %s\n" "$levelname" "$0" "$@" >&2;
    fi
}

function setLevel() {
    # Set the logging level
    #
    # Usage: setLevel <level>

    export LOGLEVEL=$1
}

# convenience functions
alias debug='log $DEBUG'
alias info='log $INFO'
alias warning='log $WARNING'
alias warn=warning
alias error='log $ERROR'
alias critical='log $CRITICAL'

Example Usage

If you want to make use of this, just save the script somewhere locally and source it

$ source logging.sh

$ setLevel $INFO

$ log $INFO "hello world"
INFO:bash: hello world

$ log $DEBUG "can't see me"

$ setLevel $DEBUG

$ debug "now you see me"
DEBUG:bash: now you see me

Better yet, throw your bash script in the trash, and re-write it in python :p

Chris.

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