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TerminalLoggers.jl

TerminalLoggers provides a logger type TerminalLogger which can format your log messages in a richer way than the default ConsoleLogger which comes with the julia standard Logging library.

Installation and setup

pkg> add TerminalLoggers

To use TerminalLogger in all your REPL sessions by default, you may add a snippet such as the following to your startup file (in .julia/config/startup.jl)

atreplinit() do repl
    try
        @eval begin
            using Logging: global_logger
            using TerminalLoggers: TerminalLogger
            global_logger(TerminalLogger())
        end
    catch
    end
end

Markdown

TerminalLogger interprets all AbstractString log messages as markdown so you can use markdown formatting to display readable formatted messages. For example,

@info """
    # A heading

    About to do the following

    * A list
    * Of actions
    * To take
    """

Progress bars

TerminalLogger displays progress logging as a set of progress bars which are cleanly separated from the rest of the program output at the bottom of the terminal.

For robust progress logging, TerminalLoggers recognizes the Progress type from the ProgressLogging package. For easy to use progress reporting you can therefore use the @progress macro:

global_logger(TerminalLogger(right_justify=120))
using ProgressLogging

@progress for i=1:100
    if i == 50
        @info "Middle of computation" i
    elseif i == 70
        println("Normal output does not interfere with progress bars")
    end
    sleep(0.01)
end
@info "Done"
Note

Rendering progress bars separately doesn't yet work on windows due to limitations of the windows console and its interaction with libuv. We expect this will eventually be solved with some combination of libuv updates and the new windows terminal.

You can also use the older progress logging API with the progress=fraction key value pair. This is simpler but has some downsides such as not interacting correctly with exceptions.

API Reference

TerminalLoggers.TerminalLogger — Type
TerminalLogger(stream=stderr, min_level=LogLevel(-1); meta_formatter=default_metafmt,
               show_limited=true, right_justify=0)

Logger with formatting optimized for interactive readability in a text console (for example, the Julia REPL). This is an enhanced version of the terminal logger Logging.ConsoleLogger which comes installed with Julia by default.

Log levels less than min_level are filtered out.

Message formatting can be controlled by setting keyword arguments:

  • meta_formatter is a function which takes the log event metadata (level, _module, group, id, file, line) and returns a color (as would be passed to printstyled), prefix and suffix for the log message. The default is to prefix with the log level and a suffix containing the module, file and line location.
  • show_limited limits the printing of large data structures to something which can fit on the screen by setting the :limit IOContext key during formatting.
  • right_justify is the integer column which log metadata is right justified at. The default is zero (metadata goes on its own line).
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