stdlog

Overview ¶

Package stdlog provides simple and fast logging to the standard output (stdout) and is optimized for programs launched via a shell or cron. It can also be used to log to a file by redirecting the standard output to a file. This package is thread-safe.

Basic examples:

logger := stdlog.GetFromFlags()
logger.Info("Connecting to the server...")
logger.Errorf("Connection failed: %q", err)

Will output:

2014-04-02 18:09:15.862 INFO Connecting to the API...
2014-04-02 18:10:14.347 ERROR Connection failed (Server is unavailable).

Log*() functions can be used to avoid evaluating arguments when it is expensive and unnecessary:

logger.Debug("Memory usage: %s", getMemoryUsage())
if LogDebug() { logger.Debug("Memory usage: %s", getMemoryUsage()) }

If debug logging is off the getMemoryUsage() will be executed on the first line while it will not be executed on the second line.

List of command-line arguments:

-log=info
    Log events at or above this level are logged.
-stderr=false
    Logs are written to standard error (stderr) instead of standard
    output.
-flushlog=none
    Until this level is reached nothing is output and logs are stored
    in the memory. Once a log event is at or above this level, it
    outputs all logs in memory as well as the future log events. This
    feature should not be used with long-running processes.

The available levels are the eight ones described in RFC 5424 (debug, info, notice, warning, error, critical, alert, emergency) and none.

Some use cases:

• By default, all logs except debug ones are output to the stdout. Which is useful to follow the execution of a program launched via a shell.
• A program launched by a crontab where the variable `MAILTO` is set with `-debug -flushlog=error` will send all logs generated by the program only if an error happens. When there is no error the email will not be sent.
• `my_program > /var/log/my_program/my_program-$(date+%Y-%m-%d-%H%M%S).log` will create a log file in /var/log/my_program each time it is run.