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1  The files in the "maintain" 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. There are various file names in the scripts and  
4  programs; they assume that the pcre directory is current.  The files in the "maint" directory of the PCRE source contain data, scripts,
5    and programs that are used for the maintenance of PCRE, but which do not form
6  132html         A Perl script that converts a .1 or .3 man page into HTML.  part of the PCRE distribution tarballs. This document describes these files and
7    also contains some notes for maintainers. Its contents are:
8  Builducptable   A Perl script that creates the contents of the ucptable.h file  
9                  from two Unicode data files, which themselves are downloaded    Files in the maint directory
10                  from the Unicode web site.    Updating to a new Unicode release
11      Preparing for a PCRE release
12  CleanTxt        A Perl script that cleans up the output of "nroff -man" by    Making a PCRE release
13                  removing backspaces and other redundant text so as to produce    Long-term ideas (wish list)
14                  a readable .txt file.  
16  Detrail         A Perl script that removes trailing spaces from files.  Files in the maint directory
17    ============================
18  Index.html      A file that is copied as index.html into the doc/html  
19                  directory. It works like this so that doc/html can be deleted  ---------------- This file is now OBSOLETE and no longer used ----------------
20                  and re-created from scratch.  Builducptable    A Perl script that creates the contents of the ucptable.h file
21                     from two Unicode data files, which themselves are downloaded
22  MakeRelease     My script for creating a new release. It processes the                   from the Unicode web site. Run this script in the "maint"
23                  documentation man pages into .text and HTML formats before                   directory.
24                  creating tarballs.  ---------------- This file is now OBSOLETE and no longer used ----------------
26  Tech.Notes      Some notes about the internals of the PCRE code.  GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
27                     that contains Unicode script names in a long string with
28  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,                   offsets, which is tedious to maintain by hand.
29                  were downloaded from the Unicode web site. They contain  
30                  information about Unicode characters and scripts.  ManyConfigTests  A shell script that runs "configure, make, test" a number of
31                     times with different configuration settings.
32  ucptest.c       A short C program for testing the Unicode property functions in  
33                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the  MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
34                  Unicode property table.                   Unicode data tables, which are themselves downloaded from the
35                     Unicode web site. Run this script in the "maint" directory.
36  ucptestdata     A directory containing two files, testinput1 and testoutput1,                   The generated file contains the tables for a 2-stage lookup
37                  to use in conjunction with the ucptest program.                   of Unicode properties.
39  utf8.c          A short C program for converting a Unicode code point into a  pcre_chartables.c.non-standard
40                  sequence of bytes in the UTF-8 encoding, and vice versa.                   This is a set of character tables that came from a Windows
41                     system. It has characters greater than 128 that are set as
42  When there is a new release of Unicode, the files in Unicode.tables must be                   spaces, amongst other things. I kept it so that it can be
43  refreshed from the web site, and the Buildupctable script can then be run to                   used for testing from time to time.
44  generate a new version of ucptable.h. The ucptest program can be used to check  
45  that the resulting table works properly, using the data files in ucptestdata to  README           This file.
46  check a number of test characters.  
47    Unicode.tables   The files in this directory, DerivedGeneralCategory.txt,
48  ****                   Scripts.txt and UnicodeData.txt, were downloaded from the
49                     Unicode web site. They contain information about Unicode
50                     characters and scripts.
52    ucptest.c        A short C program for testing the Unicode property macros
53                     that do lookups in the pcre_ucd.c data, mainly useful after
54                     rebuilding the Unicode property table. Compile and run this in
55                     the "maint" directory (see comments at its head).
57    ucptestdata      A directory containing two files, testinput1 and testoutput1,
58                     to use in conjunction with the ucptest program.
60    utf8.c           A short, freestanding C program for converting a Unicode code
61                     point into a sequence of bytes in the UTF-8 encoding, and vice
62                     versa. If its argument is a hex number such as 0x1234, it
63                     outputs a list of the equivalent UTF-8 bytes. If its argument
64                     is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
65                     treats them as a UTF-8 character and outputs the equivalent
66                     code point in hex.
69    Updating to a new Unicode release
70    =================================
72    When there is a new release of Unicode, the files in Unicode.tables must be
73    refreshed from the web site. If the new version of Unicode adds new character
74    scripts, the source file ucp.h and both the MultiStage2.py and the
75    GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
76    can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
77    run to generate the tricky tables for inclusion in pcre_tables.c.
79    If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
80    the cause is usually a missing (or misspelt) name in the list of scripts. I
81    couldn't find a straightforward list of scripts on the Unicode site, but
82    there's a useful Wikipedia page that list them, and notes the Unicode version
83    in which they were introduced:
85    http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
87    The ucptest program can be compiled and used to check that the new tables in
88    pcre_ucd.c work properly, using the data files in ucptestdata to check a number
89    of test characters. The source file ucptest.c must be updated whenever new
90    Unicode script names are added.
92    Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
93    of Unicode script names.
96    Preparing for a PCRE release
97    ============================
99    This section contains a checklist of things that I consult before building a
100    distribution for a new release.
102    . Ensure that the version number and version date are correct in configure.ac.
104    . Update the library version numbers in configure.ac according to the rules
105      given below.
107    . If new build options have been added, ensure that they are added to the CMake
108      files as well as to the autoconf files. The relevant files are CMakeLists.txt
109      and config-cmake.h.in. After making a release tarball, test it out with CMake
110      if there have been changes here.
112    . Run ./autogen.sh to ensure everything is up-to-date.
114    . Compile and test with many different config options, and combinations of
115      options. Also, test with valgrind by running "RunTest valgrind" and
116      "RunGrepTest valgrind" (which takes quite a long time). The script
117      maint/ManyConfigTests now encapsulates this testing. It runs tests with
118      different configurations, and it also runs some of them with valgrind, all of
119      which can take quite some time.
121    . Run perltest.pl on the test data for tests 1, 4, and 6. The output
122      should match the PCRE test output, apart from the version identification at
123      the start of each test. The other tests are not Perl-compatible (they use
124      various PCRE-specific features or options).
126    . It is possible to test with the emulated memmove() function by undefining
127      HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
128      may see a number of "pcre_memmove defined but not used" warnings for the
129      modules in which there is no call to memmove(). These can be ignored.
131    . Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
132      NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
133      won't need changing, but over the long term things do change.
135    . I used to test new releases myself on a number of different operating
136      systems, using different compilers as well. For example, on Solaris it is
137      helpful to test using Sun's cc compiler as a change from gcc. Adding
138      -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
139      pcretest to increase the stack size for test 2. Since I retired I can no
140      longer do this, but instead I rely on putting out release candidates for
141      folks on the pcre-dev list to test.
144    Updating version info for libtool
145    =================================
147    This set of rules for updating library version information came from a web page
148    whose URL I have forgotten. The version information consists of three parts:
149    (current, revision, age).
151    1. Start with version information of 0:0:0 for each libtool library.
153    2. Update the version information only immediately before a public release of
154       your software. More frequent updates are unnecessary, and only guarantee
155       that the current interface number gets larger faster.
157    3. If the library source code has changed at all since the last update, then
158       increment revision; c:r:a becomes c:r+1:a.
160    4. If any interfaces have been added, removed, or changed since the last
161       update, increment current, and set revision to 0.
163    5. If any interfaces have been added since the last public release, then
164       increment age.
166    6. If any interfaces have been removed or changed since the last public
167       release, then set age to 0.
169    The following explanation may help in understanding the above rules a bit
170    better. Consider that there are three possible kinds of reaction from users to
171    changes in a shared library:
173    1. Programs using the previous version may use the new version as a drop-in
174       replacement, and programs using the new version can also work with the
175       previous one. In other words, no recompiling nor relinking is needed. In
176       this case, increment revision only, don't touch current or age.
178    2. Programs using the previous version may use the new version as a drop-in
179       replacement, but programs using the new version may use APIs not present in
180       the previous one. In other words, a program linking against the new version
181       may fail if linked against the old version at run time. In this case, set
182       revision to 0, increment current and age.
184    3. Programs may need to be changed, recompiled, relinked in order to use the
185       new version. Increment current, set revision and age to 0.
188    Making a PCRE release
189    =====================
191    Run PrepareRelease and commit the files that it changes (by removing trailing
192    spaces). The first thing this script does is to run CheckMan on the man pages;
193    if it finds any markup errors, it reports them and then aborts.
195    Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
196    and the zipball. Double-check with "svn status", then create an SVN tagged
197    copy:
199      svn copy svn://vcs.exim.org/pcre/code/trunk \
200               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
202    Don't forget to update Freshmeat when the new release is out, and to tell
203    webmaster@pcre.org and the mailing list. Also, update the list of version
204    numbers in Bugzilla (edit products).
207    Future ideas (wish list)
208    ========================
210    This section records a list of ideas so that they do not get forgotten. They
211    vary enormously in their usefulness and potential for implementation. Some are
212    very sensible; some are rather wacky. Some have been on this list for years;
213    others are relatively new.
215    . Optimization
217      There are always ideas for new optimizations so as to speed up pattern
218      matching. Most of them try to save work by recognizing a non-match without
219      having to scan all the possibilities. These are some that I've recorded:
221      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
222        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
223        OTOH, this is pathological - the user could easily fix it.
225      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
226        to have little effect, and maybe makes things worse.
228      * "Ends with literal string" - note that a single character doesn't gain much
229        over the existing "required byte" (reqbyte) feature that just remembers one
230        data unit.
232      * These probably need to go in pcre_study():
234        o Remember an initial string rather than just 1 char?
236        o A required data unit from alternatives - not just the last unit, but an
237          earlier one if common to all alternatives.
239        o Friedl contains other ideas.
241      * pcre_study() does not set initial byte flags for Unicode property types
242        such as \p; I don't know how much benefit there would be for, for example,
243        setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
244        \p{N}.
246      * There is scope for more "auto-possessifying" in connection with \p and \P.
248    . If Perl gets to a consistent state over the settings of capturing sub-
249      patterns inside repeats, see if we can match it. One example of the
250      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
251      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
252      because I think it needs much more state to be remembered.
254    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
256    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
258    . Line endings:
260      * Option to use NUL as a line terminator in subject strings. This could now
261        be done relatively easily since the extension to support LF, CR, and CRLF.
262        If it is done, a suitable option for pcregrep is also required.
264    . Option to provide the pattern with a length instead of with a NUL terminator.
265      This affects quite a few places in the code and is not trivial.
267    . Catch SIGSEGV for stack overflows?
269    . A feature to suspend a match via a callout was once requested.
271    . Option to convert results into character offsets and character lengths.
273    . Option for pcregrep to scan only the start of a file. I am not keen - this is
274      the job of "head".
276    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
277      preceded by a blank line, instead of adding it to every matched line, and (b)
278      support --outputfile=name.
280    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
281      (And now presumably UTF-16 and UCP for the 16-bit library.)
283    . Add a user pointer to pcre_malloc/free functions -- some option would be
284      needed to retain backward compatibility.
286    . Define a union for the results from pcre_fullinfo().
288    . Provide a "random access to the subject" facility so that the way in which it
289      is stored is independent of PCRE. For efficiency, it probably isn't possible
290      to switch this dynamically. It would have to be specified when PCRE was
291      compiled. PCRE would then call a function every time it wanted a character.
293    . Wild thought: the ability to compile from PCRE's internal byte code to a real
294      FSM and a very fast (third) matcher to process the result. There would be
295      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
296      This is probably obsolete now that we have the JIT support.
298    . Should pcretest have some private locale data, to avoid relying on the
299      available locales for the test data, since different OS have different ideas?
300      This won't be as thorough a test, but perhaps that doesn't really matter.
302    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
303      them will of course slow it down.
305    . Someone suggested --disable-callout to save code space when callouts are
306      never wanted. This seems rather marginal.
308    . Check names that consist entirely of digits: PCRE allows, but do Perl and
309      Python, etc?
311    . A user suggested a parameter to limit the length of string matched, for
312      example if the parameter is N, the current match should fail if the matched
313      substring exceeds N. This could apply to both match functions. The value
314      could be a new field in the extra block.
316    . Callouts with arguments: (?Cn:ARG) for instance.
318    . A user is going to supply a patch to generalize the API for user-specific
319      memory allocation so that it is more flexible in threaded environments. This
320      was promised a long time ago, and never appeared. However, this is a live
321      issue not only for threaded environments, but for libraries that use PCRE and
322      want not to be beholden to their caller's memory allocation.
324    . Write a wrapper to maintain a structure with specified runtime parameters,
325      such as recurse limit, and pass these to PCRE each time it is called. Also
326      maybe malloc and free. A user sent a prototype. This relates the the previous
327      item.
329    . Write a function that generates random matching strings for a compiled regex.
331    . Pcregrep: an option to specify the output line separator, either as a string
332      or select from a fixed list. This is not dead easy, because at the moment it
333      outputs whatever is in the input file.
335    . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
336      non-thread-safe patch showed that this can help performance for patterns
337      where there are many alternatives. However, a simple thread-safe
338      implementation that I tried made things worse in many simple cases, so this
339      is not an obviously good thing.
341    . Make the longest lookbehind available via pcre_fullinfo(). This is not
342      straightforward because lookbehinds can be nested inside lookbehinds. This
343      case will have to be identified, and the amounts added. This should then give
344      the maximum possible lookbehind length. The reason for wanting this is to
345      help when implementing multi-segment matching using pcre_exec() with partial
346      matching and overlapping segments.
348    . PCRE cannot at present distinguish between subpatterns with different names,
349      but the same number (created by the use of ?|). In order to do so, a way of
350      remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
351      Now that (*MARK) has been implemented, it can perhaps be used as a way round
352      this problem.
354    . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
355      "something" and the the #ifdef appears only in one place, in "something".
357    Philip Hazel
358    Email local part: ph10
359    Email domain: cam.ac.uk
360    Last updated: 18 June 2012

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