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      1 #	$NetBSD: README,v 1.2 1998/01/09 04:12:00 perry Exp $
      2 
      3 This is a nearly-public-domain reimplementation of the V8 regexp(3) package.
      4 It gives C programs the ability to use egrep-style regular expressions, and
      5 does it in a much cleaner fashion than the analogous routines in SysV.
      6 
      7 	Copyright (c) 1986 by University of Toronto.
      8 	Written by Henry Spencer.  Not derived from licensed software.
      9 
     10 	Permission is granted to anyone to use this software for any
     11 	purpose on any computer system, and to redistribute it freely,
     12 	subject to the following restrictions:
     13 
     14 	1. The author is not responsible for the consequences of use of
     15 		this software, no matter how awful, even if they arise
     16 		from defects in it.
     17 
     18 	2. The origin of this software must not be misrepresented, either
     19 		by explicit claim or by omission.
     20 
     21 	3. Altered versions must be plainly marked as such, and must not
     22 		be misrepresented as being the original software.
     23 
     24 Barring a couple of small items in the BUGS list, this implementation is
     25 believed 100% compatible with V8.  It should even be binary-compatible,
     26 sort of, since the only fields in a "struct regexp" that other people have
     27 any business touching are declared in exactly the same way at the same
     28 location in the struct (the beginning).
     29 
     30 This implementation is *NOT* AT&T/Bell code, and is not derived from licensed
     31 software.  Even though U of T is a V8 licensee.  This software is based on
     32 a V8 manual page sent to me by Dennis Ritchie (the manual page enclosed
     33 here is a complete rewrite and hence is not covered by AT&T copyright).
     34 The software was nearly complete at the time of arrival of our V8 tape.
     35 I haven't even looked at V8 yet, although a friend elsewhere at U of T has
     36 been kind enough to run a few test programs using the V8 regexp(3) to resolve
     37 a few fine points.  I admit to some familiarity with regular-expression
     38 implementations of the past, but the only one that this code traces any
     39 ancestry to is the one published in Kernighan & Plauger (from which this
     40 one draws ideas but not code).
     41 
     42 Simplistically:  put this stuff into a source directory, copy regexp.h into
     43 /usr/include, inspect Makefile for compilation options that need changing
     44 to suit your local environment, and then do "make r".  This compiles the
     45 regexp(3) functions, compiles a test program, and runs a large set of
     46 regression tests.  If there are no complaints, then put regexp.o, regsub.o,
     47 and regerror.o into your C library, and regexp.3 into your manual-pages
     48 directory.
     49 
     50 Note that if you don't put regexp.h into /usr/include *before* compiling,
     51 you'll have to add "-I." to CFLAGS before compiling.
     52 
     53 The files are:
     54 
     55 Makefile	instructions to make everything
     56 regexp.3	manual page
     57 regexp.h	header file, for /usr/include
     58 regexp.c	source for regcomp() and regexec()
     59 regsub.c	source for regsub()
     60 regerror.c	source for default regerror()
     61 regmagic.h	internal header file
     62 try.c		source for test program
     63 timer.c		source for timing program
     64 tests		test list for try and timer
     65 
     66 This implementation uses nondeterministic automata rather than the
     67 deterministic ones found in some other implementations, which makes it
     68 simpler, smaller, and faster at compiling regular expressions, but slower
     69 at executing them.  In theory, anyway.  This implementation does employ
     70 some special-case optimizations to make the simpler cases (which do make
     71 up the bulk of regular expressions actually used) run quickly.  In general,
     72 if you want blazing speed you're in the wrong place.  Replacing the insides
     73 of egrep with this stuff is probably a mistake; if you want your own egrep
     74 you're going to have to do a lot more work.  But if you want to use regular
     75 expressions a little bit in something else, you're in luck.  Note that many
     76 existing text editors use nondeterministic regular-expression implementations,
     77 so you're in good company.
     78 
     79 This stuff should be pretty portable, given appropriate option settings.
     80 If your chars have less than 8 bits, you're going to have to change the
     81 internal representation of the automaton, although knowledge of the details
     82 of this is fairly localized.  There are no "reserved" char values except for
     83 NUL, and no special significance is attached to the top bit of chars.
     84 The string(3) functions are used a fair bit, on the grounds that they are
     85 probably faster than coding the operations in line.  Some attempts at code
     86 tuning have been made, but this is invariably a bit machine-specific.
     87