Ruby:
Writing to standard error

How to:

Ruby’s standard library provides a straightforward way to write to stderr using $stderr or STDERR. You don’t need third-party libraries for this basic operation.

Writing a simple message to stderr:

$stderr.puts "Error: File not found."
# Or equivalently
STDERR.puts "Error: File not found."

Sample output (to stderr):

Error: File not found.

Redirecting stderr to a file:

File.open('error.log', 'w') do |file|
  STDERR.reopen(file)
  STDERR.puts "Failed to open configuration."
end

This code snippet redirects stderr to a file named error.log, and all subsequent written errors will be outputted there until the program resets the stderr redirection or terminates.

Using stderr with exception handling:

begin
  # Simulating an operation that could fail, eg., opening a file
  File.open('nonexistent_file.txt')
rescue Exception => e
  STDERR.puts "Exception occurred: #{e.message}"
end

Sample output (to stderr):

Exception occurred: No such file or directory @ rb_sysopen - nonexistent_file.txt

While Ruby’s built-in methods for writing to stderr suffice for many applications, for more complex logging needs, you might consider the logger standard library or external gems like Log4r. These provide configurable logging mechanisms, including severity levels, formatting, and the ability to write to various outputs, including files, email, and more.