RegEx for matching a character in a string only if it isn't escaped

Question

How can I find and operate on a character in a string only if it isn\'t escaped (ie proceeded by an odd number of another character)?

Example:

Desired character:

Answer 1

Use a negative a lookbehind to define a boundary:

(?<!\\)(?:\\\\)*\|

See live demo here

Taking care of backslashes in Java, above regex would be:

(?<!\\\\)(?:\\\\\\\\)*\\|