org-any-link-re

org-any-link-re is a variable defined in `org.el'.
Its value is

"\\(\\[\\[\\([^][]+\\)\\]\\(\\[\\([^][]+\\)\\]\\)?\\]\\)\\|\\(<\\(doi\\|elisp\\|f\\(?:ile\\(?:\\+\\(?:\\(?:emac\\|sy\\)s\\)\\)?\\|tp\\)\\|https?\\|m\\(?:ailto\\|essage\\)\\|news\\|shell\\):\\([^]	\n
<> ][^]	\n
<>]*\\)>\\)\\|\\(\\<\\(doi\\|elisp\\|f\\(?:ile\\(?:\\+\\(?:\\(?:emac\\|sy\\)s\\)\\)?\\|tp\\)\\|https?\\|m\\(?:ailto\\|essage\\)\\|news\\|shell\\):\\([^ 	\n()<>]+\\(?:([[:word:]0-9_]+)\\|\\([^[:punct:] 	\n]\\|/\\)\\)\\)\\)"

Documentation:
Regular expression matching any link.