format a date in to the format month day, year hour:minute:second.fff am/pm in ruby

You can use strftime method of DateTime or Time class to format a date in Ruby:

main.rb
time = Time.now
puts time.strftime("%B %d, %Y %I:%M:%S.%L %p")
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Output:

main.rb
November 20, 2021 11:30:45.953 AM
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2 lines

Explanation:

• %B: full month name (e.g. November)
• %d: day of the month, zero-padded (e.g. 01)
• %Y: year with century (e.g. 2021)
• %I: hour in 12-hour clock (e.g. 05)
• %M: minute of the hour (e.g. 27)
• %S: second of the minute (e.g. 59)
• %L: millisecond of the second (e.g. 567)
• %p: either "AM" or "PM"

You can replace Time.now with your own DateTime or Time object.