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1  The files in the "maint" directory of the PCRE source contain data, scripts,  MAINTENANCE README FOR PCRE
2  and programs that are used for the maintenance of PCRE, but do not form part of  ---------------------------
3  the PCRE distribution tarballs.  
4    The files in the "maint" directory of the PCRE source contain data, scripts,
5  Builducptable   A Perl script that creates the contents of the ucptable.h file  and programs that are used for the maintenance of PCRE, but which do not form
6                  from two Unicode data files, which themselves are downloaded  part of the PCRE distribution tarballs. This document describes these files and
7                  from the Unicode web site. Run this script in the "maint"  also contains some notes for maintainers. Its contents are:
8                  directory.  
9      Files in the maint directory
10  Tech.Notes      Some notes about the internals of the PCRE code.    Updating to a new Unicode release
11      Preparing for a PCRE release
12  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,    Making a PCRE release
13                  were downloaded from the Unicode web site. They contain    Long-term ideas (wish list)
14                  information about Unicode characters and scripts.  
15    
16  ucptest.c       A short C program for testing the Unicode property functions in  Files in the maint directory
17                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the  ----------------------------
18                  Unicode property table. Compile and run this in the "main"  
19                  directory.  ----------------- This file is now OBSOLETE and no longer used ----------------
20    Builducptable    A Perl script that creates the contents of the ucptable.h file
21  ucptestdata     A directory containing two files, testinput1 and testoutput1,                   from two Unicode data files, which themselves are downloaded
22                  to use in conjunction with the ucptest program.                   from the Unicode web site. Run this script in the "maint"
23                     directory.
24  utf8.c          A short, freestanding C program for converting a Unicode code  ----------------- This file is now OBSOLETE and no longer used ----------------
25                  point into a sequence of bytes in the UTF-8 encoding, and vice  
26                  versa. If its argument is a hex number such as 0x1234, it  GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
27                  outputs a list of the equivalent UTF-8 bytes. If its argument                   that contains Unicode script names in a long string with
28                  is sequence of concatenated UTF-8 bytes (e.g. e188b4) it treats                   offsets, which is tedious to maintain by hand.
29                  them as a UTF-8 character and outputs the equivalent code point  
30                  in hex.  ManyConfigTests  A shell script that runs "configure, make, test" a number of
31                     times with different configuration settings.
32  When there is a new release of Unicode, the files in Unicode.tables must be  
33  refreshed from the web site, and the Buildupctable script can then be run to  MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
34  generate a new version of ucptable.h. The ucptest program can be used to check                   Unicode data tables, which are themselves downloaded from the
35  that the resulting table works properly, using the data files in ucptestdata to                   Unicode web site. Run this script in the "maint" directory.
36  check a number of test characters.                   The generated file contains the tables for a 2-stage lookup
37                     of Unicode properties.
38  ****  
39    README           This file.
40    
41    Unicode.tables   The files in this directory, DerivedGeneralCategory.txt,
42                     Scripts.txt and UnicodeData.txt, were downloaded from the
43                     Unicode web site. They contain information about Unicode
44                     characters and scripts.
45    
46    ucptest.c        A short C program for testing the Unicode property macros
47                     that do lookups in the pcre_ucd.c data, mainly useful after
48                     rebuilding the Unicode property table. Compile and run this in
49                     the "maint" directory (see comments at its head).
50    
51    ucptestdata      A directory containing two files, testinput1 and testoutput1,
52                     to use in conjunction with the ucptest program.
53    
54    utf8.c           A short, freestanding C program for converting a Unicode code
55                     point into a sequence of bytes in the UTF-8 encoding, and vice
56                     versa. If its argument is a hex number such as 0x1234, it
57                     outputs a list of the equivalent UTF-8 bytes. If its argument
58                     is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
59                     treats them as a UTF-8 character and outputs the equivalent
60                     code point in hex.
61    
62    
63    Updating to a new Unicode release
64    ---------------------------------
65    
66    When there is a new release of Unicode, the files in Unicode.tables must be
67    refreshed from the web site. If the new version of Unicode adds new character
68    scripts, the source file ucp.h and both the MultiStage2.py and the
69    GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
70    can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
71    run to generate the tricky tables for inclusion in pcre_tables.c.
72    
73    If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
74    the cause is usually a missing (or misspelt) name in the list of scripts. I
75    couldn't find a straightforward list of scripts on the Unicode site, but
76    there's a useful Wikipedia page that list them, and notes the Unicode version
77    in which they were introduced:
78    
79    http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
80    
81    The ucptest program can be compiled and used to check that the new tables in
82    pcre_ucd.c work properly, using the data files in ucptestdata to check a number
83    of test characters. The source file ucptest.c must be updated whenever new
84    Unicode script names are added.
85    
86    Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
87    of Unicode script names.
88    
89    
90    Preparing for a PCRE release
91    ----------------------------
92    
93    This section contains a checklist of things that I consult before building a
94    distribution for a new release.
95    
96    . Ensure that the version number and version date are correct in configure.ac.
97    
98    . If new build options have been added, ensure that they are added to the CMake
99      files as well as to the autoconf files.
100    
101    . Run ./autogen.sh to ensure everything is up-to-date.
102    
103    . Compile and test with many different config options, and combinations of
104      options. The maint/ManyConfigTests script now encapsulates this testing.
105    
106    . Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
107      be run with Perl 5.8 or 5.10; the last two require Perl 5.10. The output
108      should match the PCRE test output, apart from the version identification at
109      the start of each test. The other tests are not Perl-compatible (they use
110      various PCRE-specific features or options).
111    
112    . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
113      valgrind", though that takes quite a long time.
114    
115    . It may also useful to test with Electric Fence, though the fact that it
116      grumbles for missing free() calls can be a nuisance. (A missing free() in
117      pcretest is hardly a big problem.) To build with EF, use:
118    
119        LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
120    
121      Then all normal runs use it to check for buffer overflow. Also run everything
122      with:
123    
124        EF_PROTECT_BELOW=1 <whatever>
125    
126      because there have been problems with lookbehinds that looked too far.
127    
128    . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
129      HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
130      used" warnings for the modules in which there is no call to memmove(). These
131      can be ignored.
132    
133    . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
134      INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
135      Many of these won't need changing, but over the long term things do change.
136    
137    . Man pages: Check all man pages for \ not followed by e or f or " because
138      that indicates a markup error.
139    
140    . When the release is built, test it on a number of different operating
141      systems if possible, and using different compilers as well. For example,
142      on Solaris it is helpful to test using Sun's cc compiler as a change from
143      gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
144      needs -S 64 for pcretest to increase the stack size for test 2.
145    
146    
147    Making a PCRE release
148    ---------------------
149    
150    Run PrepareRelease and commit the files that it changes (by removing trailing
151    spaces). Then run "make distcheck" to create the tarballs and the zipball.
152    Double-check with "svn status", then create an SVN tagged copy:
153    
154      svn copy svn://vcs.exim.org/pcre/code/trunk \
155               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
156    
157    Don't forget to update Freshmeat when the new release is out, and to tell
158    webmaster@pcre.org and the mailing list.
159    
160    
161    Future ideas (wish list)
162    ------------------------
163    
164    This section records a list of ideas so that they do not get forgotten. They
165    vary enormously in their usefulness and potential for implementation. Some are
166    very sensible; some are rather wacky. Some have been on this list for years;
167    others are relatively new.
168    
169    . Optimization
170    
171      There are always ideas for new optimizations so as to speed up pattern
172      matching. Most of them try to save work by recognizing a non-match without
173      having to scan all the possibilities. These are some that I've recorded:
174    
175      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
176        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
177        OTOH, this is pathological - the user could easily fix it.
178    
179      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
180        to have little effect, and maybe makes things worse.
181    
182      * "Ends with literal string" - note that a single character doesn't gain much
183        over the existing "required byte" (reqbyte) feature that just remembers one
184        byte.
185    
186      * These probably need to go in study():
187    
188        o Remember an initial string rather than just 1 char?
189    
190        o A required byte from alternatives - not just the last char, but an
191          earlier one if common to all alternatives.
192    
193        o Friedl contains other ideas.
194    
195    . If Perl gets to a consistent state over the settings of capturing sub-
196      patterns inside repeats, see if we can match it. One example of the
197      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
198      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
199      because I think it needs much more state to be remembered.
200    
201    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
202    
203    . Unicode
204    
205      * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
206        character classes. For the moment, I've chosen not to support this for
207        backward compatibility, for speed, and because it would be messy to
208        implement.
209    
210      * A different approach to Unicode might be to use a typedef to do everything
211        in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
212        new typedef to distinguish data from bits of compiled pattern that are in
213        bytes, I think. There would need to be conversion functions in and out. I
214        don't think this is particularly trivial - and anyway, Unicode now has
215        characters that need more than 16 bits, so is this at all sensible?
216    
217      * There has been a request for direct support of 16-bit characters and
218        UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
219        is this worth it at all? One possible way of handling 16-bit characters
220        would be to "load" them in the same way that UTF-8 characters are loaded.
221    
222    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
223    
224    . Line endings:
225    
226      * Option to use NUL as a line terminator in subject strings. This could now
227        be done relatively easily since the extension to support LF, CR, and CRLF.
228        If it is done, a suitable option for pcregrep is also required.
229    
230    . Option to provide the pattern with a length instead of with a NUL terminator.
231      This affects quite a few places in the code and is not trivial.
232    
233    . Catch SIGSEGV for stack overflows?
234    
235    . A feature to suspend a match via a callout was once requested.
236    
237    . Option to convert results into character offsets and character lengths.
238    
239    . Option for pcregrep to scan only the start of a file. I am not keen - this is
240      the job of "head".
241    
242    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
243      preceded by a blank line, instead of adding it to every matched line, and (b)
244      support --outputfile=name.
245    
246    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
247    
248    . Add a user pointer to pcre_malloc/free functions -- some option would be
249      needed to retain backward compatibility.
250    
251    . Define a union for the results from pcre_fullinfo().
252    
253    . Provide a "random access to the subject" facility so that the way in which it
254      is stored is independent of PCRE. For efficiency, it probably isn't possible
255      to switch this dynamically. It would have to be specified when PCRE was
256      compiled. PCRE would then call a function every time it wanted a character.
257    
258    . Wild thought: the ability to compile from PCRE's internal byte code to a real
259      FSM and a very fast (third) matcher to process the result. There would be
260      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
261    
262    . Should pcretest have some private locale data, to avoid relying on the
263      available locales for the test data, since different OS have different ideas?
264      This won't be as thorough a test, but perhaps that doesn't really matter.
265    
266    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
267      them will of course slow it down.
268    
269    . Someone suggested --disable-callout to save code space when callouts are
270      never wanted. This seems rather marginal.
271    
272    . Check names that consist entirely of digits: PCRE allows, but do Perl and
273      Python, etc?
274    
275    . A user suggested a parameter to limit the length of string matched, for
276      example if the parameter is N, the current match should fail if the matched
277      substring exceeds N. This could apply to both match functions. The value
278      could be a new field in the extra block.
279    
280    . Callouts with arguments: (?Cn:ARG) for instance.
281    
282    . A user is going to supply a patch to generalize the API for user-specific
283      memory allocation so that it is more flexible in threaded environments. Thiw
284      was promised a long time ago, and never appeared...
285    
286    . Write a function that generates random matching strings for a compiled regex.
287    
288    . Write a wrapper to maintain a structure with specified runtime parameters,
289      such as recurse limit, and pass these to PCRE each time it is called. Also
290      maybe malloc and free. A user sent a prototype.
291    
292    . Pcregrep: an option to specify the output line separator, either as a string
293      or select from a fixed list. This is not dead easy, because at the moment it
294      outputs whatever is in the input file.
295    
296    . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
297      non-thread-safe patch showed that this can help performance for patterns
298      where there are many alternatives. However, a simple thread-safe
299      implementation that I tried made things worse in many simple cases, so this
300      is not an obviously good thing.
301    
302    . Make the longest lookbehind available via pcre_fullinfo(). This is not
303      straightforward because lookbehinds can be nested inside lookbehinds. This
304      case will have to be identified, and the amounts added. This should then give
305      the maximum possible lookbehind length. The reason for wanting this is to
306      help when implementing multi-segment matching using pcre_exec() with partial
307      matching and overlapping segments.
308    
309    . PCRE cannot at present distinguish between subpatterns with different names,
310      but the same number (created by the use of ?|). In order to do so, a way of
311      remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
312    
313    Philip Hazel
314    Email local part: ph10
315    Email domain: cam.ac.uk
316    Last updated: 26 September 2009

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