perlreapi
(1)
名称
perlreapi - perl regular expression plugin interface
用法概要
Please see following description for synopsis
描述
Perl Programmers Reference Guide PERLREAPI(1)
NAME
perlreapi - perl regular expression plugin interface
DESCRIPTION
As of Perl 5.9.5 there is a new interface for plugging and
using other regular expression engines 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, I32 minend, SV* screamer,
void* data, U32 flags);
char* (*intuit) (pTHX_ REGEXP * const rx, SV *sv, 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
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.
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Callbacks
comp
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 "msixp" flags the regex was compiled with. It also
contains additional info such as whether "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 whether
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
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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
Additional flags:
RXf_PMf_LOCALE
Set if "use locale" is in effect. If present in
"rx->extflags" "split" will use the locale dependent
definition of whitespace under when RXf_SKIPWHITE or
RXf_WHITE are in effect. Under ASCII whitespace is
defined as per isSPACE, and by the internal macros
"is_utf8_space" under UTF-8 and "isSPACE_LC" under "use
locale".
RXf_UTF8
Set if the pattern is SvUTF8(), set by Perl_pmruntime.
A regex engine may want to set or disable this flag
during compilation. The perl engine for instance may
upgrade non-UTF-8 strings to UTF-8 if the pattern
includes constructs such as "\x{...}" that can only
match Unicode values.
RXf_SPLIT
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
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 whether the subject is a UTF-8 string and
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whether 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 whether the
target string is a UTF-8 string and on whether
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 whether 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".
exec
I32 exec(pTHX_ REGEXP * const rx,
char *stringarg, char* strend, char* strbeg,
I32 minend, SV* screamer,
void* data, U32 flags);
Execute a regexp.
intuit
char* intuit(pTHX_ REGEXP * const rx,
SV *sv, 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 whether 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.
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checkstr
SV* checkstr(pTHX_ REGEXP * const rx);
Return a SV containing a string that must appear in the
pattern. Used by "split" for optimising matches.
free
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.
Numbered capture callbacks
Called to get/set the value of "$`", "$'", $& and their
named equivalents, ${^PREMATCH}, ${^POSTMATCH} and
$^{MATCH}, as well as the numbered capture buffers ($1, $2,
...).
The "paren" parameter will be "-2" for "$`", "-1" for "$'",
0 for $&, 1 for $1 and so forth.
The names have been chosen by analogy with Tie::Scalar
methods names with an additional LENGTH callback for
efficiency. However named capture variables are currently
not tied internally but implemented via magic.
numbered_buff_FETCH
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 regcomp.c for how
to untaint capture variables if that's something you'd like
your engine to do as well.
numbered_buff_STORE
void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren,
SV const * const value);
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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 always 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 base 'Tie::Scalar';
sub TIESCALAR { bless [] }
sub FETCH { undef }
sub STORE { die "This doesn't get called" }
package main;
tie my $sv => "CatptureVar";
$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
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to in the default engine.
numbered_buff_LENGTH
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.
Named capture callbacks
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
Whether "%+" or "%-" is being operated on, if any.
RXapif_ONE /* %+ */
RXapif_ALL /* %- */
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Whether 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).
named_buff
SV* (*named_buff) (pTHX_ REGEXP * const rx, SV * const key,
SV * const value, U32 flags);
named_buff_iter
SV* (*named_buff_iter) (pTHX_ REGEXP * const rx, const SV * const lastkey,
const U32 flags);
qr_package
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
whether 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.
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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);
dupe
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 old 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.
The REGEXP structure
The REGEXP struct is defined in regexp.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 is the pattern
anchored in some way, or what flags were used during the
compile, or whether 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.
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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 length of string to match */
I32 minlenret; /* mininum possible length of $& */
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 buffers */
/* 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; /* last open paren matched */
U32 lastcloseparen; /* last close paren matched */
regexp_paren_pair *swap; /* Swap copy of *offs */
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 */
/* 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:
"engine"
This field points at a regexp_engine structure which
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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".
"mother_re"
TODO, see
http://www.mail-archive.com/perl5-changes@perl.org/msg17328.html
<http://www.mail-
archive.com/perl5-changes@perl.org/msg17328.html>
"extflags"
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.
"minlen" "minlenret"
The minimum string length 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 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 whether it can do in-place substitution
which can result in considerable speedup.
"gofs"
Left offset from pos() to start match at.
"substrs"
Substring data about strings that must appear in the final
match. This is currently only used internally by perl's
engine for but might be used in the future for all engines
for optimisations.
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"nparens", "lasparen", and "lastcloseparen"
These fields are used to keep track of how many paren groups
could be matched in the pattern, which was the last open
paren to be entered, and which was the last close paren to
be entered.
"intflags"
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.
"pprivate"
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.
"swap"
Unused. Left in for compatibility with perl 5.10.0.
"offs"
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 buffer did not match. "->offs[0].start/end"
represents $& (or "${^MATCH" under "//p") and
"->offs[paren].end" matches $$paren where $paren = 1>.
"precomp" "prelen"
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 whether 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 */
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"paren_names"
This is a hash used internally to track named capture
buffers 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.
"substrs"
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.
"subbeg" "sublen" "saved_copy"
Used during execution phase for managing search and replace
patterns.
"wrapped" "wraplen"
Stores the string "qr//" stringifies to. The perl engine for
example stores "(?-xism: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 "(?:)".
"seen_evals"
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//".
"refcnt"
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.
HISTORY
Originally part of perlreguts.
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AUTHORS
Originally written by Yves Orton, expanded by var Arnfjoer`
Bjarmason.
LICENSE
Copyright 2006 Yves Orton and 2007 var Arnfjoer` Bjarmason.
This program is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/perl-512 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.cpan.org/src/5.0/perl-5.12.5.tar.bz2
Further information about this software can be found on the
open source community website at http://www.perl.org/.
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