ed is a POSIX-compliant line editor. It should work with any regular expression package that conforms to the POSIX interface standard, such as GNU regex(3). The following compiler directives are recognized: GNU_REGEX - use with GNU regex(3) DES - use to add encryption support (requires crypt(3)) NO_REALLOC_NULL - use if realloc(3) does not accept a NULL pointer The file `ed-1003.2' in the ./doc directory describes POSIX ed. Extensions to the POSIX standard are described in the file `extensions.' The ./test directory contains regression tests for ed. The README file in that directory explains how to run these. For a description of the ed algorithm, see Kernighan and Pike's book "Software Tools in Pascal," Addison-Wesley, 1981.