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Title       : 	Bash Bits: Debug Logging
Author      : 	Remy van Elst
Date        : 	15-09-2013
URL         : 	https://raymii.org/s/snippets/Bash_Bits_Debug_Logging.html
Format      : 	Markdown/HTML
Bash Bits are small examples and tips for Bash Scripts. This bash bit shows you
how to add debug logging to a bash script.

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Debug logging can be very usefull when scripts or programs don't do what you
want. I use it in most of my scripts.
First we create a simple one line function named `debug`:
    function debug() { ((DEBUG_LOG)) && echo "### $*"; }
As you can see, very simple. If the variable `DEBUG_LOG` is set, then it prints
all the text given to the function. If the variable is not set, it does nothing.
Now if we want to debug log something, we place the following line in our
    debug "This is debug output".
When we want to see the debug logging, before we run the script, we set the
variable `DEBUG_LOG` to 1:
    export DEBUG_LOG=1
    # or just for this script run:
    DEBUG_LOG=1 ./script.sh
Example with debug logging:
    [10:52:51] [remy@gateway] [ ~/conf (master) ]
    $ export DEBUG_LOG=1
    [10:52:56] [remy@gateway] [ ~/conf (master) ]
    $ ./setup.sh
    ### vimrc done
    ### screenrc done
    ### bash done
Example without debug logging:
    [10:53:11] [remy@gateway] [ ~/conf (master) ]
    $ unset DEBUG_LOG
    [10:53:11] [remy@gateway] [ ~/conf (master) ]
    $ ./setup.sh
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