PERLREAPI(1) Perl Programmers Reference Guide PERLREAPI(1)

PERLREAPI(1) Perl Programmers Reference Guide PERLREAPI(1) #

PERLREAPI(1) Perl Programmers Reference Guide PERLREAPI(1)

NNAAMMEE #

 perlreapi - Perl regular expression plugin interface

DDEESSCCRRIIPPTTIIOONN #

 As of Perl 5.9.5 there is a new interface for plugging and using regular
 expression engines other than the default one.

 Each engine is supposed to provide access to a constant structure of the
 following format:

     typedef struct regexp_engine {
         REGEXP* (*comp) (pTHX_
                          const SV * const pattern, const U32 flags);
         I32     (*exec) (pTHX_
                          REGEXP * const rx,
                          char* stringarg,
                          char* strend, char* strbeg,
                          SSize_t minend, SV* sv,
                          void* data, U32 flags);
         char*   (*intuit) (pTHX_
                            REGEXP * const rx, SV *sv,
                            const char * const strbeg,
                            char *strpos, char *strend, U32 flags,
                            struct re_scream_pos_data_s *data);
         SV*     (*checkstr) (pTHX_ REGEXP * const rx);
         void    (*free) (pTHX_ REGEXP * const rx);
         void    (*numbered_buff_FETCH) (pTHX_
                                         REGEXP * const rx,
                                         const I32 paren,
                                         SV * const sv);
         void    (*numbered_buff_STORE) (pTHX_
                                         REGEXP * const rx,
                                         const I32 paren,
                                         SV const * const value);
         I32     (*numbered_buff_LENGTH) (pTHX_
                                          REGEXP * const rx,
                                          const SV * const sv,
                                          const I32 paren);
         SV*     (*named_buff) (pTHX_
                                REGEXP * const rx,
                                SV * const key,
                                SV * const value,
                                U32 flags);
         SV*     (*named_buff_iter) (pTHX_
                                     REGEXP * const rx,
                                     const SV * const lastkey,
                                     const U32 flags);
         SV*     (*qr_package)(pTHX_ REGEXP * const rx);
     #ifdef USE_ITHREADS
         void*   (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
     #endif
         REGEXP* (*op_comp) (...);

 When a regexp is compiled, its "engine" field is then set to point at the
 appropriate structure, so that when it needs to be used Perl can find the
 right routines to do so.

 In order to install a new regexp handler, $^H{regcomp} is set to an
 integer which (when casted appropriately) resolves to one of these
 structures.  When compiling, the "comp" method is executed, and the
 resulting "regexp" structure's engine field is expected to point back at
 the same structure.

 The pTHX_ symbol in the definition is a macro used by Perl under
 threading to provide an extra argument to the routine holding a pointer
 back to the interpreter that is executing the regexp. So under threading
 all routines get an extra argument.

CCaallllbbaacckkss ccoommpp REGEXP* comp(pTHX_ const SV * const pattern, const U32 flags);

 Compile the pattern stored in "pattern" using the given "flags" and
 return a pointer to a prepared "REGEXP" structure that can perform the
 match.  See "The REGEXP structure" below for an explanation of the
 individual fields in the REGEXP struct.

 The "pattern" parameter is the scalar that was used as the pattern.
 Previous versions of Perl would pass two "char*" indicating the start and
 end of the stringified pattern; the following snippet can be used to get
 the old parameters:

     STRLEN plen;
     char*  exp = SvPV(pattern, plen);
     char* xend = exp + plen;

 Since any scalar can be passed as a pattern, it's possible to implement
 an engine that does something with an array (""ook" =~ [ qw/ eek hlagh /
 ]") or with the non-stringified form of a compiled regular expression
 (""ook" =~ qr/eek/").  Perl's own engine will always stringify everything
 using the snippet above, but that doesn't mean other engines have to.

 The "flags" parameter is a bitfield which indicates which of the "msixpn"
 flags the regex was compiled with.  It also contains additional info,
 such as if "use locale" is in effect.

 The "eogc" flags are stripped out before being passed to the comp
 routine.  The regex engine does not need to know if any of these are set,
 as those flags should only affect what Perl does with the pattern and its
 match variables, not how it gets compiled and executed.

 By the time the comp callback is called, some of these flags have already
 had effect (noted below where applicable).  However most of their effect
 occurs after the comp callback has run, in routines that read the
 "rx->extflags" field which it populates.

 In general the flags should be preserved in "rx->extflags" after
 compilation, although the regex engine might want to add or delete some
 of them to invoke or disable some special behavior in Perl.  The flags
 along with any special behavior they cause are documented below:

 The pattern modifiers:

 "/m" - RXf_PMf_MULTILINE
     If this is in "rx->extflags" it will be passed to "Perl_fbm_instr" by
     "pp_split" which will treat the subject string as a multi-line
     string.

 "/s" - RXf_PMf_SINGLELINE
 "/i" - RXf_PMf_FOLD
 "/x" - RXf_PMf_EXTENDED
     If present on a regex, "#" comments will be handled differently by
     the tokenizer in some cases.

     TODO: Document those cases.

 "/p" - RXf_PMf_KEEPCOPY
     TODO: Document this

 Character set
     The character set rules are determined by an enum that is contained
     in this field.  This is still experimental and subject to change, but
     the current interface returns the rules by use of the in-line
     function "get_regex_charset(const U32 flags)".  The only currently
     documented value returned from it is REGEX_LOCALE_CHARSET, which is
     set if "use locale" is in effect. If present in "rx->extflags",
     "split" will use the locale dependent definition of whitespace when
     RXf_SKIPWHITE or RXf_WHITE is in effect.  ASCII whitespace is defined
     as per isSPACE, and by the internal macros "is_utf8_space" under
     UTF-8, and "isSPACE_LC" under "use locale".

 Additional flags:

 RXf_SPLIT
     This flag was removed in perl 5.18.0.  "split ' '" is now special-
     cased solely in the parser.  RXf_SPLIT is still #defined, so you can
     test for it.  This is how it used to work:

     If "split" is invoked as "split ' '" or with no arguments (which
     really means "split(' ', $_)", see split), Perl will set this flag.
     The regex engine can then check for it and set the SKIPWHITE and
     WHITE extflags.  To do this, the Perl engine does:

         if (flags & RXf_SPLIT && r->prelen == 1 && r->precomp[0] == ' ')
             r->extflags |= (RXf_SKIPWHITE|RXf_WHITE);

 These flags can be set during compilation to enable optimizations in the
 "split" operator.

 RXf_SKIPWHITE
     This flag was removed in perl 5.18.0.  It is still #defined, so you
     can set it, but doing so will have no effect.  This is how it used to
     work:

     If the flag is present in "rx->extflags" "split" will delete
     whitespace from the start of the subject string before it's operated
     on.  What is considered whitespace depends on if the subject is a
     UTF-8 string and if the "RXf_PMf_LOCALE" flag is set.

     If RXf_WHITE is set in addition to this flag, "split" will behave
     like "split " "" under the Perl engine.

 RXf_START_ONLY
     Tells the split operator to split the target string on newlines
     ("\n") without invoking the regex engine.

     Perl's engine sets this if the pattern is "/^/" ("plen == 1 && *exp
     == '^'"), even under "/^/s"; see split.  Of course a different regex
     engine might want to use the same optimizations with a different
     syntax.

 RXf_WHITE
     Tells the split operator to split the target string on whitespace
     without invoking the regex engine.  The definition of whitespace
     varies depending on if the target string is a UTF-8 string and on if
     RXf_PMf_LOCALE is set.

     Perl's engine sets this flag if the pattern is "\s+".

 RXf_NULL
     Tells the split operator to split the target string on characters.
     The definition of character varies depending on if the target string
     is a UTF-8 string.

     Perl's engine sets this flag on empty patterns, this optimization
     makes "split //" much faster than it would otherwise be.  It's even
     faster than "unpack".

 RXf_NO_INPLACE_SUBST
     Added in perl 5.18.0, this flag indicates that a regular expression
     might perform an operation that would interfere with inplace
     substitution. For instance it might contain lookbehind, or assign to
     non-magical variables (such as $REGMARK and $REGERROR) during
     matching.  "s///" will skip certain optimisations when this is set.

eexxeecc I32 exec(pTHX_ REGEXP * const rx, char stringarg, char strend, char* strbeg, SSize_t minend, SV* sv, void* data, U32 flags);

 Execute a regexp. The arguments are

 rx  The regular expression to execute.

 sv  This is the SV to be matched against.  Note that the actual char
     array to be matched against is supplied by the arguments described
     below; the SV is just used to determine UTF8ness, "pos()" etc.

 strbeg
     Pointer to the physical start of the string.

 strend
     Pointer to the character following the physical end of the string
     (i.e.  the "\0", if any).

 stringarg
     Pointer to the position in the string where matching should start; it
     might not be equal to "strbeg" (for example in a later iteration of
     "/.../g").

 minend
     Minimum length of string (measured in bytes from "stringarg") that
     must match; if the engine reaches the end of the match but hasn't
     reached this position in the string, it should fail.

 data
     Optimisation data; subject to change.

 flags
     Optimisation flags; subject to change.

iinnttuuiitt char* intuit(pTHX_ REGEXP * const rx, SV *sv, const char * const strbeg, char *strpos, char *strend, const U32 flags, struct re_scream_pos_data_s *data);

 Find the start position where a regex match should be attempted, or
 possibly if the regex engine should not be run because the pattern can't
 match.  This is called, as appropriate, by the core, depending on the
 values of the "extflags" member of the "regexp" structure.

 Arguments:

     rx:     the regex to match against
     sv:     the SV being matched: only used for utf8 flag; the string
             itself is accessed via the pointers below. Note that on
             something like an overloaded SV, SvPOK(sv) may be false
             and the string pointers may point to something unrelated to
             the SV itself.
     strbeg: real beginning of string
     strpos: the point in the string at which to begin matching
     strend: pointer to the byte following the last char of the string
     flags   currently unused; set to 0
     data:   currently unused; set to NULL

cchheecckkssttrr SV* checkstr(pTHX_ REGEXP * const rx);

 Return a SV containing a string that must appear in the pattern. Used by
 "split" for optimising matches.

ffrreeee void free(pTHX_ REGEXP * const rx);

 Called by Perl when it is freeing a regexp pattern so that the engine can
 release any resources pointed to by the "pprivate" member of the "regexp"
 structure.  This is only responsible for freeing private data; Perl will
 handle releasing anything else contained in the "regexp" structure.

NNuummbbeerreedd ccaappttuurree ccaallllbbaacckkss Called to get/set the value of “$`”, “$’”, $& and their named equivalents, ${^PREMATCH}, ${^POSTMATCH} and ${^MATCH}, as well as the numbered capture groups ($1, $2, …).

 The "paren" parameter will be 1 for $1, 2 for $2 and so forth, and have
 these symbolic values for the special variables:

${^PREMATCH} RX_BUFF_IDX_CARET_PREMATCH #

${^POSTMATCH} RX_BUFF_IDX_CARET_POSTMATCH #

${^MATCH} RX_BUFF_IDX_CARET_FULLMATCH #

$` RX_BUFF_IDX_PREMATCH #

$’ RX_BUFF_IDX_POSTMATCH #

$& RX_BUFF_IDX_FULLMATCH #

 Note that in Perl 5.17.3 and earlier, the last three constants were also
 used for the caret variants of the variables.

 The names have been chosen by analogy with Tie::Scalar methods names with
 an additional LLEENNGGTTHH callback for efficiency.  However named capture
 variables are currently not tied internally but implemented via magic.

 _n_u_m_b_e_r_e_d___b_u_f_f___F_E_T_C_H

     void numbered_buff_FETCH(pTHX_ REGEXP * const rx, const I32 paren,
                              SV * const sv);

 Fetch a specified numbered capture.  "sv" should be set to the scalar to
 return, the scalar is passed as an argument rather than being returned
 from the function because when it's called Perl already has a scalar to
 store the value, creating another one would be redundant.  The scalar can
 be set with "sv_setsv", "sv_setpvn" and friends, see perlapi.

 This callback is where Perl untaints its own capture variables under
 taint mode (see perlsec).  See the "Perl_reg_numbered_buff_fetch"
 function in _r_e_g_c_o_m_p_._c for how to untaint capture variables if that's
 something you'd like your engine to do as well.

 _n_u_m_b_e_r_e_d___b_u_f_f___S_T_O_R_E

     void    (*numbered_buff_STORE) (pTHX_
                                     REGEXP * const rx,
                                     const I32 paren,
                                     SV const * const value);

 Set the value of a numbered capture variable.  "value" is the scalar that
 is to be used as the new value.  It's up to the engine to make sure this
 is used as the new value (or reject it).

 Example:

     if ("ook" =~ /(o*)/) {
         # 'paren' will be '1' and 'value' will be 'ee'
         $1 =~ tr/o/e/;
     }

 Perl's own engine will croak on any attempt to modify the capture
 variables, to do this in another engine use the following callback
 (copied from "Perl_reg_numbered_buff_store"):

     void
     Example_reg_numbered_buff_store(pTHX_
                                     REGEXP * const rx,
                                     const I32 paren,
                                     SV const * const value)
     {
         PERL_UNUSED_ARG(rx);
         PERL_UNUSED_ARG(paren);
         PERL_UNUSED_ARG(value);

         if (!PL_localizing)
             Perl_croak(aTHX_ PL_no_modify);
     }

 Actually Perl will not _a_l_w_a_y_s croak in a statement that looks like it
 would modify a numbered capture variable.  This is because the STORE
 callback will not be called if Perl can determine that it doesn't have to
 modify the value.  This is exactly how tied variables behave in the same
 situation:

     package CaptureVar;
     use parent 'Tie::Scalar';

     sub TIESCALAR { bless [] }
     sub FETCH { undef }
     sub STORE { die "This doesn't get called" }

     package main;

     tie my $sv => "CaptureVar";
     $sv =~ y/a/b/;

 Because $sv is "undef" when the "y///" operator is applied to it, the
 transliteration won't actually execute and the program won't "die".  This
 is different to how 5.8 and earlier versions behaved since the capture
 variables were READONLY variables then; now they'll just die when
 assigned to in the default engine.

 _n_u_m_b_e_r_e_d___b_u_f_f___L_E_N_G_T_H

     I32 numbered_buff_LENGTH (pTHX_
                               REGEXP * const rx,
                               const SV * const sv,
                               const I32 paren);

 Get the "length" of a capture variable.  There's a special callback for
 this so that Perl doesn't have to do a FETCH and run "length" on the
 result, since the length is (in Perl's case) known from an offset stored
 in "rx->offs", this is much more efficient:

     I32 s1  = rx->offs[paren].start;
     I32 s2  = rx->offs[paren].end;
     I32 len = t1 - s1;

 This is a little bit more complex in the case of UTF-8, see what
 "Perl_reg_numbered_buff_length" does with is_utf8_string_loclen.

NNaammeedd ccaappttuurree ccaallllbbaacckkss Called to get/set the value of “%+” and “%-”, as well as by some utility functions in re.

 There are two callbacks, "named_buff" is called in all the cases the
 FETCH, STORE, DELETE, CLEAR, EXISTS and SCALAR Tie::Hash callbacks would
 be on changes to "%+" and "%-" and "named_buff_iter" in the same cases as
 FIRSTKEY and NEXTKEY.

 The "flags" parameter can be used to determine which of these operations
 the callbacks should respond to.  The following flags are currently
 defined:

 Which Tie::Hash operation is being performed from the Perl level on "%+"
 or "%+", if any:

     RXapif_FETCH
     RXapif_STORE
     RXapif_DELETE
     RXapif_CLEAR
     RXapif_EXISTS
     RXapif_SCALAR
     RXapif_FIRSTKEY
     RXapif_NEXTKEY

 If "%+" or "%-" is being operated on, if any.

     RXapif_ONE /* %+ */
     RXapif_ALL /* %- */

 If this is being called as "re::regname", "re::regnames" or
 "re::regnames_count", if any.  The first two will be combined with
 "RXapif_ONE" or "RXapif_ALL".

     RXapif_REGNAME
     RXapif_REGNAMES
     RXapif_REGNAMES_COUNT

 Internally "%+" and "%-" are implemented with a real tied interface via
 Tie::Hash::NamedCapture.  The methods in that package will call back into
 these functions.  However the usage of Tie::Hash::NamedCapture for this
 purpose might change in future releases.  For instance this might be
 implemented by magic instead (would need an extension to mgvtbl).

 _n_a_m_e_d___b_u_f_f

     SV*     (*named_buff) (pTHX_ REGEXP * const rx, SV * const key,
                            SV * const value, U32 flags);

 _n_a_m_e_d___b_u_f_f___i_t_e_r

     SV*     (*named_buff_iter) (pTHX_
                                 REGEXP * const rx,
                                 const SV * const lastkey,
                                 const U32 flags);

qqrr__ppaacckkaaggee SV* qr_package(pTHX_ REGEXP * const rx);

 The package the qr// magic object is blessed into (as seen by "ref
 qr//").  It is recommended that engines change this to their package name
 for identification regardless of if they implement methods on the object.

 The package this method returns should also have the internal "Regexp"
 package in its @ISA.  "qr//->isa("Regexp")" should always be true
 regardless of what engine is being used.

 Example implementation might be:

SV* #

     Example_qr_package(pTHX_ REGEXP * const rx)
     {
         PERL_UNUSED_ARG(rx);
         return newSVpvs("re::engine::Example");
     }

 Any method calls on an object created with "qr//" will be dispatched to
 the package as a normal object.

     use re::engine::Example;
     my $re = qr//;
     $re->meth; # dispatched to re::engine::Example::meth()

 To retrieve the "REGEXP" object from the scalar in an XS function use the
 "SvRX" macro, see "REGEXP Functions" in perlapi.

     void meth(SV * rv)

PPCODE: #

         REGEXP * re = SvRX(sv);

dduuppee void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param);

 On threaded builds a regexp may need to be duplicated so that the pattern
 can be used by multiple threads.  This routine is expected to handle the
 duplication of any private data pointed to by the "pprivate" member of
 the "regexp" structure.  It will be called with the preconstructed new
 "regexp" structure as an argument, the "pprivate" member will point at
 the oolldd private structure, and it is this routine's responsibility to
 construct a copy and return a pointer to it (which Perl will then use to
 overwrite the field as passed to this routine.)

 This allows the engine to dupe its private data but also if necessary
 modify the final structure if it really must.

 On unthreaded builds this field doesn't exist.

oopp__ccoommpp This is private to the Perl core and subject to change. Should be left null.

TThhee RREEGGEEXXPP ssttrruuccttuurree The REGEXP struct is defined in _r_e_g_e_x_p_._h. All regex engines must be able to correctly build such a structure in their “comp” routine.

 The REGEXP structure contains all the data that Perl needs to be aware of
 to properly work with the regular expression.  It includes data about
 optimisations that Perl can use to determine if the regex engine should
 really be used, and various other control info that is needed to properly
 execute patterns in various contexts, such as if the pattern anchored in
 some way, or what flags were used during the compile, or if the program
 contains special constructs that Perl needs to be aware of.

 In addition it contains two fields that are intended for the private use
 of the regex engine that compiled the pattern.  These are the "intflags"
 and "pprivate" members.  "pprivate" is a void pointer to an arbitrary
 structure, whose use and management is the responsibility of the
 compiling engine.  Perl will never modify either of these values.

     typedef struct regexp {
         /* what engine created this regexp? */
         const struct regexp_engine* engine;

         /* what re is this a lightweight copy of? */
         struct regexp* mother_re;

         /* Information about the match that the Perl core uses to manage
          * things */
         U32 extflags;   /* Flags used both externally and internally */
         I32 minlen;     /* mininum possible number of chars in */
                            string to match */
         I32 minlenret;  /* mininum possible number of chars in $& */
         U32 gofs;       /* chars left of pos that we search from */

         /* substring data about strings that must appear
            in the final match, used for optimisations */
         struct reg_substr_data *substrs;

         U32 nparens;  /* number of capture groups */

         /* private engine specific data */
         U32 intflags;   /* Engine Specific Internal flags */
         void *pprivate; /* Data private to the regex engine which
                            created this object. */

         /* Data about the last/current match. These are modified during
          * matching*/
         U32 lastparen;            /* highest close paren matched ($+) */
         U32 lastcloseparen;       /* last close paren matched ($^N) */
         regexp_paren_pair *offs;  /* Array of offsets for (@-) and
                                      (@+) */

         char *subbeg;  /* saved or original string so \digit works
                           forever. */
         SV_SAVED_COPY  /* If non-NULL, SV which is COW from original */
         I32 sublen;    /* Length of string pointed by subbeg */
         I32 suboffset;  /* byte offset of subbeg from logical start of
                            str */
         I32 subcoffset; /* suboffset equiv, but in chars (for @-/@+) */

         /* Information about the match that isn't often used */
         I32 prelen;           /* length of precomp */
         const char *precomp;  /* pre-compilation regular expression */

         char *wrapped;  /* wrapped version of the pattern */
         I32 wraplen;    /* length of wrapped */

         I32 seen_evals;   /* number of eval groups in the pattern - for
                              security checks */
         HV *paren_names;  /* Optional hash of paren names */

         /* Refcount of this regexp */
         I32 refcnt;             /* Refcount of this regexp */
     } regexp;

 The fields are discussed in more detail below:

“"eennggiinnee"” This field points at a “regexp_engine” structure which contains pointers to the subroutines that are to be used for performing a match. It is the compiling routine’s responsibility to populate this field before returning the regexp object.

 Internally this is set to "NULL" unless a custom engine is specified in
 $^H{regcomp}, Perl's own set of callbacks can be accessed in the struct
 pointed to by "RE_ENGINE_PTR".

“"mmootthheerr__rree"” TODO, see commit 28d8d7f41a.

“"eexxttffllaaggss"” This will be used by Perl to see what flags the regexp was compiled with, this will normally be set to the value of the flags parameter by the comp callback. See the comp documentation for valid flags.

“"mmiinnlleenn"” “"mmiinnlleennrreett"” The minimum string length (in characters) required for the pattern to match. This is used to prune the search space by not bothering to match any closer to the end of a string than would allow a match. For instance there is no point in even starting the regex engine if the minlen is 10 but the string is only 5 characters long. There is no way that the pattern can match.

 "minlenret" is the minimum length (in characters) of the string that
 would be found in $& after a match.

 The difference between "minlen" and "minlenret" can be seen in the
 following pattern:

     /ns(?=\d)/

 where the "minlen" would be 3 but "minlenret" would only be 2 as the \d
 is required to match but is not actually included in the matched content.
 This distinction is particularly important as the substitution logic uses
 the "minlenret" to tell if it can do in-place substitutions (these can
 result in considerable speed-up).

“"ggooffss"” Left offset from ppooss(()) to start match at.

“"ssuubbssttrrss"” Substring data about strings that must appear in the final match. This is currently only used internally by Perl’s engine, but might be used in the future for all engines for optimisations.

“"nnppaarreennss"”,, “"llaassttppaarreenn"”,, aanndd “"llaassttcclloosseeppaarreenn"” These fields are used to keep track of: how many paren capture groups there are in the pattern; which was the highest paren to be closed (see “$+” in perlvar); and which was the most recent paren to be closed (see “$^N” in perlvar).

“"iinnttffllaaggss"” The engine’s private copy of the flags the pattern was compiled with. Usually this is the same as “extflags” unless the engine chose to modify one of them.

“"pppprriivvaattee"” A void* pointing to an engine-defined data structure. The Perl engine uses the “regexp_internal” structure (see “Base Structures” in perlreguts) but a custom engine should use something else.

“"ooffffss"” A “regexp_paren_pair” structure which defines offsets into the string being matched which correspond to the $& and $1, $2 etc. captures, the “regexp_paren_pair” struct is defined as follows:

     typedef struct regexp_paren_pair {
         I32 start;
         I32 end;
     } regexp_paren_pair;

 If "->offs[num].start" or "->offs[num].end" is "-1" then that capture
 group did not match.  "->offs[0].start/end" represents $& (or "${^MATCH}"
 under "/p") and "->offs[paren].end" matches $$paren where $paren = 1>.

“"pprreeccoommpp"” “"pprreelleenn"” Used for optimisations. “precomp” holds a copy of the pattern that was compiled and “prelen” its length. When a new pattern is to be compiled (such as inside a loop) the internal “regcomp” operator checks if the last compiled “REGEXP”’s “precomp” and “prelen” are equivalent to the new one, and if so uses the old pattern instead of compiling a new one.

 The relevant snippet from "Perl_pp_regcomp":

         if (!re || !re->precomp || re->prelen != (I32)len ||
             memNE(re->precomp, t, len))
         /* Compile a new pattern */

“"ppaarreenn__nnaammeess"” This is a hash used internally to track named capture groups and their offsets. The keys are the names of the buffers the values are dualvars, with the IV slot holding the number of buffers with the given name and the pv being an embedded array of I32. The values may also be contained independently in the data array in cases where named backreferences are used.

“"ssuubbssttrrss"” Holds information on the longest string that must occur at a fixed offset from the start of the pattern, and the longest string that must occur at a floating offset from the start of the pattern. Used to do Fast-Boyer- Moore searches on the string to find out if its worth using the regex engine at all, and if so where in the string to search.

“"ssuubbbbeegg"” “"ssuubblleenn"” “"ssaavveedd__ccooppyy"” “"ssuubbooffffsseett"” “"ssuubbccooffffsseett"” Used during the execution phase for managing search and replace patterns, and for providing the text for $&, $1 etc. “subbeg” points to a buffer (either the original string, or a copy in the case of “RX_MATCH_COPIED(rx)”), and “sublen” is the length of the buffer. The “RX_OFFS” start and end indices index into this buffer.

 In the presence of the "REXEC_COPY_STR" flag, but with the addition of
 the "REXEC_COPY_SKIP_PRE" or "REXEC_COPY_SKIP_POST" flags, an engine can
 choose not to copy the full buffer (although it must still do so in the
 presence of "RXf_PMf_KEEPCOPY" or the relevant bits being set in
 "PL_sawampersand").  In this case, it may set "suboffset" to indicate the
 number of bytes from the logical start of the buffer to the physical
 start (i.e. "subbeg").  It should also set "subcoffset", the number of
 characters in the offset. The latter is needed to support "@-" and "@+"
 which work in characters, not bytes.

“"wwrraappppeedd"” “"wwrraapplleenn"” Stores the string “qr//” stringifies to. The Perl engine for example stores “(?^:eek)” in the case of “qr/eek/”.

 When using a custom engine that doesn't support the "(?:)" construct for
 inline modifiers, it's probably best to have "qr//" stringify to the
 supplied pattern, note that this will create undesired patterns in cases
 such as:

     my $x = qr/a|b/;  # "a|b"
     my $y = qr/c/i;   # "c"
     my $z = qr/$x$y/; # "a|bc"

 There's no solution for this problem other than making the custom engine
 understand a construct like "(?:)".

“"sseeeenn__eevvaallss"” This stores the number of eval groups in the pattern. This is used for security purposes when embedding compiled regexes into larger patterns with “qr//”.

“"rreeffccnntt"” The number of times the structure is referenced. When this falls to 0, the regexp is automatically freed by a call to “pregfree”. This should be set to 1 in each engine’s “comp” routine.

HHIISSTTOORRYY #

 Originally part of perlreguts.

AAUUTTHHOORRSS #

 Originally written by Yves Orton, expanded by Ævar Arnfjörð Bjarmason.

LLIICCEENNSSEE #

 Copyright 2006 Yves Orton and 2007 Ævar Arnfjörð Bjarmason.

 This program is free software; you can redistribute it and/or modify it
 under the same terms as Perl itself.

perl v5.36.3 2023-02-15 PERLREAPI(1)