URL detection

# This regexp (for php preg_replace) should match any URLs in text (beginning with protocol or by www.)
# BUT only if they are not encapsulated by $ ($http://somewhere$ MUST NOT be matched).
#
# At first it is here splited to parts for easier reading
# EDIT: Moved punctuation inside the outer parentheses
#
# ------- this is here for checking the $ sign at the beginning -------#
(?<!\$)(?<!\$http:\/\/)(?<!\$https:\/\/)(?<!\$ftp:\/\/)(?<!\$ftps:\/\/)

#-- detect protocol or www ----#
((((https?|ftps?):\/\/)|(www\.))

# everything except spaces and so - I'm counting with IDN.
# And strip punctuation from the end
(\S+\.\S+)*[^\s,.?!])

# check if the $ is not at the end
(?!\$)

# full regex without splitting
(?<!\$)(?<!\$http:\/\/)(?<!\$https:\/\/)(?<!\$ftp:\/\/)(?<!\$ftps:\/\/)((((https?|ftps?):\/\/)|(www\.))(\S+\.\S+)*[^\s,.?!])(?!\$)