|
There are two ways to enable debugging output for regular expressions.
If your perl is compiled with -DDEBUGGING, you may use the -Dr flag on
the command line.
Otherwise, one can use re 'debug', which has effects at compile time and run
time. It is not lexically scoped.
The debugging output at compile time looks like this:
Compiling REx `[bc]d(ef*g)+h[ij]k$'
size 45 Got 364 bytes for offset annotations.
first at 1
rarest char g at 0
rarest char d at 0
1: ANYOF[bc](12)
12: EXACT <d>(14)
14: CURLYX[0] {1,32767}(28)
16: OPEN1(18)
18: EXACT <e>(20)
20: STAR(23)
21: EXACT <f>(0)
23: EXACT <g>(25)
25: CLOSE1(27)
27: WHILEM[1/1](0)
28: NOTHING(29)
29: EXACT <h>(31)
31: ANYOF[ij](42)
42: EXACT <k>(44)
44: EOL(45)
45: END(0)
anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating)
stclass `ANYOF[bc]' minlen 7
Offsets: [45]
1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
Omitting $` $& $' support.
|
|
The first line shows the pre-compiled form of the regex. The second shows the size of the
compiled form (in arbitrary units, usually 4-byte words) and the total number of bytes
allocated for the offset/length table, usually 4+size*8. The next line shows the
label id of the first node that does a match.
The
anchored `de' at 1 floating `gh' at 3..2147483647 (checking floating)
stclass `ANYOF[bc]' minlen 7
|
|
line (split into two lines above) contains optimizer information. In the example shown, the
optimizer found that the match should contain a substring de at offset 1, plus
substring gh at some offset between 3 and infinity. Moreover, when checking for
these substrings (to abandon impossible matches quickly), Perl will check for the substring gh
before checking for the substring de. The optimizer may also use the knowledge
that the match starts (at the first id) with a character class, and no
string shorter than 7 characters can possibly match.
The fields of interest which may appear in this line are
anchored STRING at POS
-
floating STRING at
POS1..POS2
- See above.
matching floating/anchored
- Which substring to check first.
minlen
- The minimal length of the match.
stclass TYPE
- Type of first matching node.
noscan
- Don't scan for the found substrings.
isall
- Means that the optimizer information is all that the regular expression contains, and
thus one does not need to enter the regex engine at all.
GPOS
- Set if the pattern contains
\G.
plus
- Set if the pattern starts with a repeated char (as in
x+y).
implicit
- Set if the pattern starts with
.*.
with eval
- Set if the pattern contain eval-groups, such as
(?{ code }) and (??{
code }).
anchored(TYPE)
- If the pattern may match only at a handful of places, (with
TYPE being BOL,
MBOL, or GPOS. See the table below.
If a substring is known to match at end-of-line only, it may be followed by $,
as in floating `k'$.
The optimizer-specific information is used to avoid entering (a slow) regex engine on
strings that will not definitely match. If the isall flag is set, a call to the
regex engine may be avoided even when the optimizer found an appropriate place for the match.
Above the optimizer section is the list of nodes of the compiled form of the regex.
Each line has format
id: TYPE OPTIONAL-INFO (next-id)
Here are the possible types, with short descriptions:
# TYPE arg-description [num-args] [longjump-len] DESCRIPTION
# Exit points
END no End of program.
SUCCEED no Return from a subroutine, basically.
# Anchors:
BOL no Match "" at beginning of line.
MBOL no Same, assuming multiline.
SBOL no Same, assuming singleline.
EOS no Match "" at end of string.
EOL no Match "" at end of line.
MEOL no Same, assuming multiline.
SEOL no Same, assuming singleline.
BOUND no Match "" at any word boundary
BOUNDL no Match "" at any word boundary
NBOUND no Match "" at any word non-boundary
NBOUNDL no Match "" at any word non-boundary
GPOS no Matches where last m//g left off.
# [Special] alternatives
ANY no Match any one character (except newline).
SANY no Match any one character.
ANYOF sv Match character in (or not in) this class.
ALNUM no Match any alphanumeric character
ALNUML no Match any alphanumeric char in locale
NALNUM no Match any non-alphanumeric character
NALNUML no Match any non-alphanumeric char in locale
SPACE no Match any whitespace character
SPACEL no Match any whitespace char in locale
NSPACE no Match any non-whitespace character
NSPACEL no Match any non-whitespace char in locale
DIGIT no Match any numeric character
NDIGIT no Match any non-numeric character
# BRANCH The set of branches constituting a single choice are hooked
# together with their "next" pointers, since precedence prevents
# anything being concatenated to any individual branch. The
# "next" pointer of the last BRANCH in a choice points to the
# thing following the whole choice. This is also where the
# final "next" pointer of each individual branch points; each
# branch starts with the operand node of a BRANCH node.
#
BRANCH node Match this alternative, or the next...
# BACK Normal "next" pointers all implicitly point forward; BACK
# exists to make loop structures possible.
# not used
BACK no Match "", "next" ptr points backward.
# Literals
EXACT sv Match this string (preceded by length).
EXACTF sv Match this string, folded (prec. by length).
EXACTFL sv Match this string, folded in locale (w/len).
# Do nothing
NOTHING no Match empty string.
# A variant of above which delimits a group, thus stops optimizations
TAIL no Match empty string. Can jump here from outside.
# STAR,PLUS '?', and complex '*' and '+', are implemented as circular
# BRANCH structures using BACK. Simple cases (one character
# per match) are implemented with STAR and PLUS for speed
# and to minimize recursive plunges.
#
STAR node Match this (simple) thing 0 or more times.
PLUS node Match this (simple) thing 1 or more times.
CURLY sv 2 Match this simple thing {n,m} times.
CURLYN no 2 Match next-after-this simple thing
# {n,m} times, set parens.
CURLYM no 2 Match this medium-complex thing {n,m} times.
CURLYX sv 2 Match this complex thing {n,m} times.
# This terminator creates a loop structure for CURLYX
WHILEM no Do curly processing and see if rest matches.
# OPEN,CLOSE,GROUPP ...are numbered at compile time.
OPEN num 1 Mark this point in input as start of #n.
CLOSE num 1 Analogous to OPEN.
REF num 1 Match some already matched string
REFF num 1 Match already matched string, folded
REFFL num 1 Match already matched string, folded in loc.
# grouping assertions
IFMATCH off 1 2 Succeeds if the following matches.
UNLESSM off 1 2 Fails if the following matches.
SUSPEND off 1 1 "Independent" sub-regex.
IFTHEN off 1 1 Switch, should be preceded by switcher .
GROUPP num 1 Whether the group matched.
# Support for long regex
LONGJMP off 1 1 Jump far away.
BRANCHJ off 1 1 BRANCH with long offset.
# The heavy worker
EVAL evl 1 Execute some Perl code.
# Modifiers
MINMOD no Next operator is not greedy.
LOGICAL no Next opcode should set the flag only.
# This is not used yet
RENUM off 1 1 Group with independently numbered parens.
# This is not really a node, but an optimized away piece of a "long" node.
# To simplify debugging output, we mark it as if it were a node
OPTIMIZED off Placeholder for dump.
|
|
Following the optimizer information is a dump of the offset/length table, here split across
several lines:
Offsets: [45]
1[4] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 5[1]
0[0] 12[1] 0[0] 6[1] 0[0] 7[1] 0[0] 9[1] 8[1] 0[0] 10[1] 0[0]
11[1] 0[0] 12[0] 12[0] 13[1] 0[0] 14[4] 0[0] 0[0] 0[0] 0[0]
0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 18[1] 0[0] 19[1] 20[0]
|
|
The first line here indicates that the offset/length table contains 45 entries. Each entry
is a pair of integers, denoted by offset[length]. Entries are numbered starting
with 1, so entry #1 here is 1[4] and entry #12 is 5[1]. 1[4]
indicates that the node labeled 1: (the 1: ANYOF[bc]) begins at
character position 1 in the pre-compiled form of the regex, and has a length of 4 characters. 5[1]
in position 12 indicates that the node labeled 12: (the 12: EXACT <d>)
begins at character position 5 in the pre-compiled form of the regex, and has a length of 1
character. 12[1] in position 14 indicates that the node labeled 14:
(the 14: CURLYX[0] {1,32767}) begins at character position 12 in the pre-compiled
form of the regex, and has a length of 1 character---that is, it corresponds to the +
symbol in the precompiled regex.
0[0] items indicate that there is no corresponding node.
First of all, when doing a match, one may get no run-time output even if debugging is
enabled. This means that the regex engine was never entered and that all of the job was
therefore done by the optimizer.
If the regex engine was entered, the output may look like this:
Matching `[bc]d(ef*g)+h[ij]k$' against `abcdefg__gh__'
Setting an EVAL scope, savestack=3
2 <ab> <cdefg__gh_> | 1: ANYOF
3 <abc> <defg__gh_> | 11: EXACT <d>
4 <abcd> <efg__gh_> | 13: CURLYX {1,32767}
4 <abcd> <efg__gh_> | 26: WHILEM
0 out of 1..32767 cc=effff31c
4 <abcd> <efg__gh_> | 15: OPEN1
4 <abcd> <efg__gh_> | 17: EXACT <e>
5 <abcde> <fg__gh_> | 19: STAR
EXACT <f> can match 1 times out of 32767...
Setting an EVAL scope, savestack=3
6 <bcdef> <g__gh__> | 22: EXACT <g>
7 <bcdefg> <__gh__> | 24: CLOSE1
7 <bcdefg> <__gh__> | 26: WHILEM
1 out of 1..32767 cc=effff31c
Setting an EVAL scope, savestack=12
7 <bcdefg> <__gh__> | 15: OPEN1
7 <bcdefg> <__gh__> | 17: EXACT <e>
restoring \1 to 4(4)..7
failed, try continuation...
7 <bcdefg> <__gh__> | 27: NOTHING
7 <bcdefg> <__gh__> | 28: EXACT <h>
failed...
failed...
|
|
The most significant information in the output is about the particular node of the
compiled regex that is currently being tested against the target string. The format of these
lines is
STRING-OFFSET <PRE-STRING> <POST-STRING> |ID: TYPE
The TYPE info is indented with respect to the backtracking level. Other incidental
information appears interspersed within.
|
|
