Question

I need help decoding this regular expression from sprockets. I am not sure what this matches but if someone give give me some hints or starting points.

HEADER_PATTERN = /
\A (
  (?m:\s*) (
   (\/\* (?m:.*?) \*\/) |
   (\#\#\# (?m:.*?) \#\#\#) |
   (\/\/ .* \n?)+ |
   (\# .* \n?)+
  )
 )+
/x

Answer 1

HEADER_PATTERN = /
\A (                             # Start of string
  (?m:\s*) (                     # Match optional whitespace
   (\/\* (?m:.*?) \*\/) |        # Either match /* (any characters, lazily) */
   (\#\#\# (?m:.*?) \#\#\#) |    # or ### (any characters, lazily) ###
   (\/\/ .* \n?)+ |              # or // (any characters except newlines) until optional newline (one or more)
   (\# .* \n?)+                  # or # (any characters except newlines) until optional newline (one or more)
  )
 )+                              # once or more
/x

(?m:...) allows the dot inside this sub-expression also to match newline characters which is usually doesn’t. (This is a Ruby specialty; nearly all other regex flavors use (?s:...) for this)

So it seems this regex matches block comments or line comments at the start of a file/string.