What is the OR operator in emacs regexps?

Question

The manual says to use \'\\|\', as in a\\|b matches a or b. But when I use it with regexp builder or align-regexp e.g. with, \"True\\|False\", it doesn\'t recognize \"True\" or

Answer 1

For further details, see the discussion of '\' and strings in the elisp manual section 34.3.1.1 "Special Characters in Regular Expressions"

M-: (info "(elisp) Regexp Special") RET

Answer 2

Use double escape: \\|

A Few Additional Notes:

Emacs has 2 escaping styles, one in EmacsLisp the other when used in commands,
ie. from the M-x prompt (rgrep, occur, …)

In EmacsLisp, use the double backslash \\|

…

From M-x … use a single backslash \|

… As a side note, when writing embedded EmacsLisp, for example in yasnippet dynamic expansions, you have to use a quadruple backslash: \\\\| (to escape the double backslashes.)

Always avoid this (if possible), for example in yasnippet you can provide mode related emacslisp, without the additional escaping, via a .yas-setup.el