freebsd-src/bin/ed

ed is an 8-bit-clean, POSIX-compliant line editor.  It should work with
any regular expression package that conforms to the POSIX interface
standard, such as GNU regex(3).

If reliable signals are supported (e.g., POSIX sigaction(2)), it should
compile with little trouble.  Otherwise, the macros SPL1() and SPL0()
should be redefined to disable interrupts.

The following compiler directives are recognized:
NO_REALLOC_NULL	- if realloc(3) does not accept a NULL pointer
BACKWARDS	- for backwards compatibility
NEED_INSQUE	- if insque(3) is missing

The file `POSIX' describes extensions to and deviations from the POSIX
standard.

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 Plauger's book
"Software Tools in Pascal," Addison-Wesley, 1981.