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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    pcre_chartables.c.non-standard
40                     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                     spaces, amongst other things. I kept it so that it can be
43                     used for testing from time to time.
44    
45    README           This file.
46    
47    Unicode.tables   The files in this directory (CaseFolding.txt,
48                     DerivedGeneralCategory.txt, GraphemeBreakProperty.txt,
49                     Scripts.txt and UnicodeData.txt) were downloaded from the
50                     Unicode web site. They contain information about Unicode
51                     characters and scripts.
52    
53    ucptest.c        A short C program for testing the Unicode property macros
54                     that do lookups in the pcre_ucd.c data, mainly useful after
55                     rebuilding the Unicode property table. Compile and run this in
56                     the "maint" directory (see comments at its head).
57    
58    ucptestdata      A directory containing two files, testinput1 and testoutput1,
59                     to use in conjunction with the ucptest program.
60    
61    utf8.c           A short, freestanding C program for converting a Unicode code
62                     point into a sequence of bytes in the UTF-8 encoding, and vice
63                     versa. If its argument is a hex number such as 0x1234, it
64                     outputs a list of the equivalent UTF-8 bytes. If its argument
65                     is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
66                     treats them as a UTF-8 character and outputs the equivalent
67                     code point in hex.
68    
69    
70    Updating to a new Unicode release
71    =================================
72    
73    When there is a new release of Unicode, the files in Unicode.tables must be
74    refreshed from the web site. If the new version of Unicode adds new character
75    scripts, the source file ucp.h and both the MultiStage2.py and the
76    GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
77    can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
78    run to generate the tricky tables for inclusion in pcre_tables.c.
79    
80    If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
81    the cause is usually a missing (or misspelt) name in the list of scripts. I
82    couldn't find a straightforward list of scripts on the Unicode site, but
83    there's a useful Wikipedia page that list them, and notes the Unicode version
84    in which they were introduced:
85    
86    http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
87    
88    The ucptest program can be compiled and used to check that the new tables in
89    pcre_ucd.c work properly, using the data files in ucptestdata to check a number
90    of test characters. The source file ucptest.c must be updated whenever new
91    Unicode script names are added.
92    
93    Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
94    of Unicode script names.
95    
96    
97    Preparing for a PCRE release
98    ============================
99    
100    This section contains a checklist of things that I consult before building a
101    distribution for a new release.
102    
103    . Ensure that the version number and version date are correct in configure.ac.
104    
105    . Update the library version numbers in configure.ac according to the rules
106      given below.
107    
108    . If new build options have been added, ensure that they are added to the CMake
109      files as well as to the autoconf files. The relevant files are CMakeLists.txt
110      and config-cmake.h.in. After making a release tarball, test it out with CMake
111      if there have been changes here.
112    
113    . Run ./autogen.sh to ensure everything is up-to-date.
114    
115    . Compile and test with many different config options, and combinations of
116      options. Also, test with valgrind by running "RunTest valgrind" and
117      "RunGrepTest valgrind" (which takes quite a long time). The script
118      maint/ManyConfigTests now encapsulates this testing. It runs tests with
119      different configurations, and it also runs some of them with valgrind, all of
120      which can take quite some time.
121    
122    . Run perltest.pl on the test data for tests 1, 4, and 6. The output
123      should match the PCRE test output, apart from the version identification at
124      the start of each test. The other tests are not Perl-compatible (they use
125      various PCRE-specific features or options).
126    
127    . It is possible to test with the emulated memmove() function by undefining
128      HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
129      may see a number of "pcre_memmove defined but not used" warnings for the
130      modules in which there is no call to memmove(). These can be ignored.
131    
132    . Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
133      NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
134      won't need changing, but over the long term things do change.
135    
136    . I used to test new releases myself on a number of different operating
137      systems, using different compilers as well. For example, on Solaris it is
138      helpful to test using Sun's cc compiler as a change from gcc. Adding
139      -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
140      pcretest to increase the stack size for test 2. Since I retired I can no
141      longer do this, but instead I rely on putting out release candidates for
142      folks on the pcre-dev list to test.
143    
144    
145    Updating version info for libtool
146    =================================
147    
148    This set of rules for updating library version information came from a web page
149    whose URL I have forgotten. The version information consists of three parts:
150    (current, revision, age).
151    
152    1. Start with version information of 0:0:0 for each libtool library.
153    
154    2. Update the version information only immediately before a public release of
155       your software. More frequent updates are unnecessary, and only guarantee
156       that the current interface number gets larger faster.
157    
158    3. If the library source code has changed at all since the last update, then
159       increment revision; c:r:a becomes c:r+1:a.
160    
161    4. If any interfaces have been added, removed, or changed since the last
162       update, increment current, and set revision to 0.
163    
164    5. If any interfaces have been added since the last public release, then
165       increment age.
166    
167    6. If any interfaces have been removed or changed since the last public
168       release, then set age to 0.
169    
170    The following explanation may help in understanding the above rules a bit
171    better. Consider that there are three possible kinds of reaction from users to
172    changes in a shared library:
173    
174    1. Programs using the previous version may use the new version as a drop-in
175       replacement, and programs using the new version can also work with the
176       previous one. In other words, no recompiling nor relinking is needed. In
177       this case, increment revision only, don't touch current or age.
178    
179    2. Programs using the previous version may use the new version as a drop-in
180       replacement, but programs using the new version may use APIs not present in
181       the previous one. In other words, a program linking against the new version
182       may fail if linked against the old version at run time. In this case, set
183       revision to 0, increment current and age.
184    
185    3. Programs may need to be changed, recompiled, relinked in order to use the
186       new version. Increment current, set revision and age to 0.
187    
188    
189    Making a PCRE release
190    =====================
191    
192    Run PrepareRelease and commit the files that it changes (by removing trailing
193    spaces). The first thing this script does is to run CheckMan on the man pages;
194    if it finds any markup errors, it reports them and then aborts.
195    
196    Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
197    and the zipball. Double-check with "svn status", then create an SVN tagged
198    copy:
199    
200      svn copy svn://vcs.exim.org/pcre/code/trunk \
201               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
202    
203    Don't forget to update Freshmeat when the new release is out, and to tell
204    webmaster@pcre.org and the mailing list. Also, update the list of version
205    numbers in Bugzilla (edit products).
206    
207    
208    Future ideas (wish list)
209    ========================
210    
211    This section records a list of ideas so that they do not get forgotten. They
212    vary enormously in their usefulness and potential for implementation. Some are
213    very sensible; some are rather wacky. Some have been on this list for years;
214    others are relatively new.
215    
216    . Optimization
217    
218      There are always ideas for new optimizations so as to speed up pattern
219      matching. Most of them try to save work by recognizing a non-match without
220      having to scan all the possibilities. These are some that I've recorded:
221    
222      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
223        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
224        OTOH, this is pathological - the user could easily fix it.
225    
226      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
227        to have little effect, and maybe makes things worse.
228    
229      * "Ends with literal string" - note that a single character doesn't gain much
230        over the existing "required byte" (reqbyte) feature that just remembers one
231        data unit.
232    
233      * These probably need to go in pcre_study():
234    
235        o Remember an initial string rather than just 1 char?
236    
237        o A required data unit from alternatives - not just the last unit, but an
238          earlier one if common to all alternatives.
239    
240        o Friedl contains other ideas.
241    
242      * pcre_study() does not set initial byte flags for Unicode property types
243        such as \p; I don't know how much benefit there would be for, for example,
244        setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
245        \p{N}.
246    
247      * There is scope for more "auto-possessifying" in connection with \p and \P.
248    
249    . If Perl gets to a consistent state over the settings of capturing sub-
250      patterns inside repeats, see if we can match it. One example of the
251      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
252      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
253      because I think it needs much more state to be remembered.
254    
255    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
256    
257    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
258    
259    . Line endings:
260    
261      * Option to use NUL as a line terminator in subject strings. This could now
262        be done relatively easily since the extension to support LF, CR, and CRLF.
263        If it is done, a suitable option for pcregrep is also required.
264    
265    . Option to provide the pattern with a length instead of with a NUL terminator.
266      This affects quite a few places in the code and is not trivial.
267    
268    . Catch SIGSEGV for stack overflows?
269    
270    . A feature to suspend a match via a callout was once requested.
271    
272    . Option to convert results into character offsets and character lengths.
273    
274    . Option for pcregrep to scan only the start of a file. I am not keen - this is
275      the job of "head".
276    
277    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
278      preceded by a blank line, instead of adding it to every matched line, and (b)
279      support --outputfile=name.
280    
281    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
282      (And now presumably UTF-16 and UCP for the 16-bit library.)
283    
284    . Add a user pointer to pcre_malloc/free functions -- some option would be
285      needed to retain backward compatibility.
286    
287    . Define a union for the results from pcre_fullinfo().
288    
289    . Provide a "random access to the subject" facility so that the way in which it
290      is stored is independent of PCRE. For efficiency, it probably isn't possible
291      to switch this dynamically. It would have to be specified when PCRE was
292      compiled. PCRE would then call a function every time it wanted a character.
293    
294    . Wild thought: the ability to compile from PCRE's internal byte code to a real
295      FSM and a very fast (third) matcher to process the result. There would be
296      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
297      This is probably obsolete now that we have the JIT support.
298    
299    . Should pcretest have some private locale data, to avoid relying on the
300      available locales for the test data, since different OS have different ideas?
301      This won't be as thorough a test, but perhaps that doesn't really matter.
302    
303    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
304      them will of course slow it down.
305    
306    . Someone suggested --disable-callout to save code space when callouts are
307      never wanted. This seems rather marginal.
308    
309    . Check names that consist entirely of digits: PCRE allows, but do Perl and
310      Python, etc?
311    
312    . A user suggested a parameter to limit the length of string matched, for
313      example if the parameter is N, the current match should fail if the matched
314      substring exceeds N. This could apply to both match functions. The value
315      could be a new field in the extra block.
316    
317    . Callouts with arguments: (?Cn:ARG) for instance.
318    
319    . A user is going to supply a patch to generalize the API for user-specific
320      memory allocation so that it is more flexible in threaded environments. This
321      was promised a long time ago, and never appeared. However, this is a live
322      issue not only for threaded environments, but for libraries that use PCRE and
323      want not to be beholden to their caller's memory allocation.
324    
325    . Write a wrapper to maintain a structure with specified runtime parameters,
326      such as recurse limit, and pass these to PCRE each time it is called. Also
327      maybe malloc and free. A user sent a prototype. This relates the the previous
328      item.
329    
330    . Write a function that generates random matching strings for a compiled regex.
331    
332    . Pcregrep: an option to specify the output line separator, either as a string
333      or select from a fixed list. This is not dead easy, because at the moment it
334      outputs whatever is in the input file.
335    
336    . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
337      non-thread-safe patch showed that this can help performance for patterns
338      where there are many alternatives. However, a simple thread-safe
339      implementation that I tried made things worse in many simple cases, so this
340      is not an obviously good thing.
341    
342    . Make the longest lookbehind available via pcre_fullinfo(). This is not
343      straightforward because lookbehinds can be nested inside lookbehinds. This
344      case will have to be identified, and the amounts added. This should then give
345      the maximum possible lookbehind length. The reason for wanting this is to
346      help when implementing multi-segment matching using pcre_exec() with partial
347      matching and overlapping segments.
348    
349    . PCRE cannot at present distinguish between subpatterns with different names,
350      but the same number (created by the use of ?|). In order to do so, a way of
351      remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
352      Now that (*MARK) has been implemented, it can perhaps be used as a way round
353      this problem.
354    
355    . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
356      "something" and the the #ifdef appears only in one place, in "something".
357    
358    Philip Hazel
359    Email local part: ph10
360    Email domain: cam.ac.uk
361    Last updated: 20 September 2012

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