A logger configured via an environment variable.
See the documentation for the log crate for more information about its API.
Log levels are controlled on a per-module basis, and by default all logging
is disabled except for
error!. Logging is controlled via the
environment variable. The value of this environment variable is a
comma-separated list of logging directives. A logging directive is of the
The path to the module is rooted in the name of the crate it was compiled
for, so if your program is contained in a file
hello.rs, for example, to
turn on logging for this file you would use a value of
Furthermore, this path is a prefix-search, so all modules nested in the
specified module will also have logging enabled.
log_level is optional to specify. If omitted, all logging will
be enabled. If specified, it must be one of the strings
As the log level for a module is optional, the module to enable logging for
is also optional. If only a
log_level is provided, then the global log
level for all modules is set to this value.
Some examples of valid values of
helloturns on all logging for the 'hello' module
infoturns on all info logging
hello=debugturns on debug logging for 'hello'
hello,std::optionturns on hello, and std's option logging
error,hello=warnturn on global error logging and also warn for hello
A RUST_LOG directive may include a regex filter. The syntax is to append
followed by a regex. Each message is checked against the regex, and is only
logged if it matches. Note that the matching is done after formatting the
log string but before adding any logging meta-data. There is a single filter
for all modules.
hello/footurns on all logging for the 'hello' module where the log message includes 'foo'.
info/f.oturns on all info logging where the log message includes 'foo', 'f1o', 'fao', etc.
hello=debug/foo*footurns on debug logging for 'hello' where the log message includes 'foofoo' or 'fofoo' or 'fooooooofoo', etc.
error,hello=warn/[0-9] scopesturn on global error logging and also warn for hello. In both cases the log message must include a single digit number followed by 'scopes'.
LogBuilder acts as builder for initializing the EnvLogger. It can be used change the enviromental variable used to provide the logging directives and also set the default log level filter.
Use a default