Daftar Isi

• NAME
• DESCRIPTION
• Debugger Internals
  • Writing Your Own Debugger
• Frame Listing Output Examples
• Debugging Regular Expressions
  • Compile-time Output
  • Types of Nodes
  • Run-time Output
• Debugging Perl Memory Usage
  • Using $ENV{PERL_DEBUG_MSTATS}
• SEE ALSO

NAME

perldebguts - Guts of Perl debugging

DESCRIPTION

This is not perldebug, which tells you how to usethe debugger. This manpage describes low-level details concerningthe debugger's internals, which range from difficult to impossibleto understand for anyone who isn't incredibly intimate with Perl's guts.Caveat lector.

Debugger Internals

Perl has special debugging hooks at compile-time and run-time usedto create debugging environments. These hooks are not to be confusedwith the perl -Dxxx command described in perlrun, which isusable only if a special Perl is built per the instructions in theINSTALL podpage in the Perl source tree.

For example, whenever you call Perl's built-in caller functionfrom the package DB, the arguments that the corresponding stackframe was called with are copied to the @DB::args array. Thesemechanisms are enabled by calling Perl with the -d switch.Specifically, the following additional features are enabled(cf. $^P in perlvar):

• Perl inserts the contents of $ENV{PERL5DB} (or BEGIN {require'perl5db.pl'} if not present) before the first line of your program.

• Each array @{"_<$filename"} holds the lines of $filename for afile compiled by Perl. The same is also true for evaled stringsthat contain subroutines, or which are currently being executed.The $filename for evaled strings looks like (eval 34).Code assertions in regexes look like (re_eval 19).

  Values in this array are magical in numeric context: they compareequal to zero only if the line is not breakable.

• Each hash %{"_<$filename"} contains breakpoints and actions keyedby line number. Individual entries (as opposed to the whole hash)are settable. Perl only cares about Boolean true here, althoughthe values used by perl5db.pl have the form"$break_condition\0$action".

  The same holds for evaluated strings that contain subroutines, orwhich are currently being executed. The $filename for evaled stringslooks like (eval 34) or (re_eval 19).

• Each scalar ${"_<$filename"} contains "_<$filename". This isalso the case for evaluated strings that contain subroutines, orwhich are currently being executed. The $filename for evaledstrings looks like (eval 34) or (re_eval 19).

• After each required file is compiled, but before it is executed,DB::postponed(*{"_<$filename"}) is called if the subroutineDB::postponed exists. Here, the $filename is the expanded name ofthe required file, as found in the values of %INC.

• After each subroutine subname is compiled, the existence of$DB::postponed{subname} is checked. If this key exists,DB::postponed(subname) is called if the DB::postponed subroutinealso exists.

• A hash %DB::sub is maintained, whose keys are subroutine namesand whose values have the form filename:startline-endline.filename has the form (eval 34) for subroutines defined insideevals, or (re_eval 19) for those within regex code assertions.

• When the execution of your program reaches a point that can hold abreakpoint, the DB::DB() subroutine is called if any of the variables$DB::trace, $DB::single, or $DB::signal is true. These variablesare not localizable. This feature is disabled when executinginside DB::DB(), including functions called from it unless $^D & (1<<30) is true.

• When execution of the program reaches a subroutine call, a call to&DB::sub(args) is made instead, with $DB::sub holding thename of the called subroutine. (This doesn't happen if the subroutinewas compiled in the DB package.)

Note that if &DB::sub needs external data for it to work, nosubroutine call is possible without it. As an example, the standarddebugger's &DB::sub depends on the $DB::deep variable(it defines how many levels of recursion deep into the debugger you can gobefore a mandatory break). If $DB::deep is not defined, subroutinecalls are not possible, even though &DB::sub exists.

Writing Your Own Debugger

Environment Variables

The PERL5DB environment variable can be used to define a debugger.For example, the minimal "working" debugger (it actually doesn't do anything)consists of one line:

  sub DB::DB {}
 

It can easily be defined like this:

  $ PERL5DB="sub DB::DB {}" perl -d your-script
 

Another brief debugger, slightly more useful, can be createdwith only the line:

  sub DB::DB {print ++$i; scalar <STDIN>}
 

This debugger prints a number which increments for each statementencountered and waits for you to hit a newline before continuingto the next statement.

The following debugger is actually useful:

  {
 
 package DB;
 
 sub DB  {}
 
 sub sub {print ++$i, " $sub\n"; &$sub}
 
  }
 

It prints the sequence number of each subroutine call and the name of thecalled subroutine. Note that &DB::sub is being compiled into thepackage DB through the use of the package directive.

When it starts, the debugger reads your rc file (./.perldb or~/.perldb under Unix), which can set important options.(A subroutine (&afterinit) can be defined here as well; it is executedafter the debugger completes its own initialization.)

After the rc file is read, the debugger reads the PERLDB_OPTSenvironment variable and uses it to set debugger options. Thecontents of this variable are treated as if they were the argumentof an o ... debugger command (q.v. in Configurable Options in perldebug).

Debugger Internal Variables

In addition to the file and subroutine-related variables mentioned above,the debugger also maintains various magical internal variables.

• @DB::dbline is an alias for @{"::_<current_file"}, whichholds the lines of the currently-selected file (compiled by Perl), eitherexplicitly chosen with the debugger's f command, or implicitly by flowof execution.

  Values in this array are magical in numeric context: they compareequal to zero only if the line is not breakable.

• %DB::dbline is an alias for %{"::_<current_file"}, whichcontains breakpoints and actions keyed by line number inthe currently-selected file, either explicitly chosen with thedebugger's f command, or implicitly by flow of execution.

  As previously noted, individual entries (as opposed to the whole hash)are settable. Perl only cares about Boolean true here, althoughthe values used by perl5db.pl have the form"$break_condition\0$action".

Debugger Customization Functions

Some functions are provided to simplify customization.

• See Configurable Options in perldebug for a description of options parsed byDB::parse_options(string).

• DB::dump_trace(skip[,count]) skips the specified number of framesand returns a list containing information about the calling frames (allof them, if count is missing). Each entry is reference to a hashwith keys context (either ., $, or @), sub (subroutinename, or info about eval), args (undef or a reference toan array), file, and line.

• DB::print_trace(FH, skip[, count[, short]]) printsformatted info about caller frames. The last two functions may beconvenient as arguments to <, << commands.

Note that any variables and functions that are not documented inthis manpages (or in perldebug) are considered for internal use only, and as such are subject to change without notice.

Frame Listing Output Examples

The frame option can be used to control the output of frame information. For example, contrast this expression trace:

 $ perl -de 42
 
 Stack dump during die enabled outside of evals.
 
 
 Loading DB routines from perl5db.pl patch level 0.94
 
 Emacs support available.
 
 
 Enter h or 'h h' for help.
 
 
 main::(-e:1):   0
 
   DB<1> sub foo { 14 }
 
 
   DB<2> sub bar { 3 }
 
 
   DB<3> t print foo() * bar()
 
 main::((eval 172):3):   print foo() + bar();
 
 main::foo((eval 168):2):
 
 main::bar((eval 170):2):
 
 42
 

with this one, once the option frame=2 has been set:

   DB<4> o f=2
 
 frame = '2'
 
   DB<5> t print foo() * bar()
 
 3:  foo() * bar()
 
 entering main::foo
 
  2: sub foo { 14 };
 
 exited main::foo
 
 entering main::bar
 
  2: sub bar { 3 };
 
 exited main::bar
 
 42
 

By way of demonstration, we present below a laborious listingresulting from setting your PERLDB_OPTS environment variable tothe value f=n N, and running perl -d -V from the command line.Examples using various values of n are shown to give you a feelfor the difference between settings. Long though it may be, thisis not a complete listing, but only excerpts.

1

  entering main::BEGIN
 
   entering Config::BEGIN
 
 Package lib/Exporter.pm.
 
 Package lib/Carp.pm.
 
   Package lib/Config.pm.
 
   entering Config::TIEHASH
 
   entering Exporter::import
 
 entering Exporter::export
 
  entering Config::myconfig
 
   entering Config::FETCH
 
   entering Config::FETCH
 
   entering Config::FETCH
 
   entering Config::FETCH
 

2

  entering main::BEGIN
 
   entering Config::BEGIN
 
 Package lib/Exporter.pm.
 
 Package lib/Carp.pm.
 
   exited Config::BEGIN
 
   Package lib/Config.pm.
 
   entering Config::TIEHASH
 
   exited Config::TIEHASH
 
   entering Exporter::import
 
 entering Exporter::export
 
 exited Exporter::export
 
   exited Exporter::import
 
  exited main::BEGIN
 
  entering Config::myconfig
 
   entering Config::FETCH
 
   exited Config::FETCH
 
   entering Config::FETCH
 
   exited Config::FETCH
 
   entering Config::FETCH
 

3

  in  $=main::BEGIN() from /dev/null:0
 
   in  $=Config::BEGIN() from lib/Config.pm:2
 
 Package lib/Exporter.pm.
 
 Package lib/Carp.pm.
 
   Package lib/Config.pm.
 
   in  $=Config::TIEHASH('Config') from lib/Config.pm:644
 
   in  $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
 in  $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from li
 
  in  @=Config::myconfig() from /dev/null:0
 
   in  $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'osname') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'osvers') from lib/Config.pm:574
 

4

  in  $=main::BEGIN() from /dev/null:0
 
   in  $=Config::BEGIN() from lib/Config.pm:2
 
 Package lib/Exporter.pm.
 
 Package lib/Carp.pm.
 
   out $=Config::BEGIN() from lib/Config.pm:0
 
   Package lib/Config.pm.
 
   in  $=Config::TIEHASH('Config') from lib/Config.pm:644
 
   out $=Config::TIEHASH('Config') from lib/Config.pm:644
 
   in  $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
 in  $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
 
 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/
 
   out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
  out $=main::BEGIN() from /dev/null:0
 
  in  @=Config::myconfig() from /dev/null:0
 
   in  $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
 
   out $=Config::FETCH(ref(Config), 'package') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
 
   out $=Config::FETCH(ref(Config), 'baserev') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
 
   out $=Config::FETCH(ref(Config), 'PERL_VERSION') from lib/Config.pm:574
 
   in  $=Config::FETCH(ref(Config), 'PERL_SUBVERSION') from lib/Config.pm:574
 

5

  in  $=main::BEGIN() from /dev/null:0
 
   in  $=Config::BEGIN() from lib/Config.pm:2
 
 Package lib/Exporter.pm.
 
 Package lib/Carp.pm.
 
   out $=Config::BEGIN() from lib/Config.pm:0
 
   Package lib/Config.pm.
 
   in  $=Config::TIEHASH('Config') from lib/Config.pm:644
 
   out $=Config::TIEHASH('Config') from lib/Config.pm:644
 
   in  $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
 in  $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
 
 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/E
 
   out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
  out $=main::BEGIN() from /dev/null:0
 
  in  @=Config::myconfig() from /dev/null:0
 
   in  $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
 
   out $=Config::FETCH('Config=HASH(0x1aa444)', 'package') from lib/Config.pm:574
 
   in  $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
 
   out $=Config::FETCH('Config=HASH(0x1aa444)', 'baserev') from lib/Config.pm:574
 

6

  in  $=CODE(0x15eca4)() from /dev/null:0
 
   in  $=CODE(0x182528)() from lib/Config.pm:2
 
 Package lib/Exporter.pm.
 
   out $=CODE(0x182528)() from lib/Config.pm:0
 
   scalar context return from CODE(0x182528): undef
 
   Package lib/Config.pm.
 
   in  $=Config::TIEHASH('Config') from lib/Config.pm:628
 
   out $=Config::TIEHASH('Config') from lib/Config.pm:628
 
   scalar context return from Config::TIEHASH:   empty hash
 
   in  $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
 in  $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
 
 out $=Exporter::export('Config', 'main', 'myconfig', 'config_vars') from lib/Exporter.pm:171
 
 scalar context return from Exporter::export: ''
 
   out $=Exporter::import('Config', 'myconfig', 'config_vars') from /dev/null:0
 
   scalar context return from Exporter::import: ''
 

In all cases shown above, the line indentation shows the call tree.If bit 2 of frame is set, a line is printed on exit from asubroutine as well. If bit 4 is set, the arguments are printedalong with the caller info. If bit 8 is set, the arguments areprinted even if they are tied or references. If bit 16 is set, thereturn value is printed, too.

When a package is compiled, a line like this

 Package lib/Carp.pm.
 

is printed with proper indentation.

Debugging Regular Expressions

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 atcompile time and run time. Since Perl 5.9.5, this pragma is lexicallyscoped.

Compile-time Output

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 secondshows the size of the compiled form (in arbitrary units, usually4-byte words) and the total number of bytes allocated for theoffset/length table, usually 4+size*8. The next line shows thelabel 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 optimizerinformation. In the example shown, the optimizer found that the match should contain a substring de at offset 1, plus substring ghat some offset between 3 and infinity. Moreover, when checking forthese substrings (to abandon impossible matches quickly), Perl will checkfor the substring gh before checking for the substring de. Theoptimizer may also use the knowledge that the match starts (at thefirst 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 regularexpression contains, and thus one does not need to enter the regex engine atall.

• 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 TYPEbeing BOL, MBOL, or GPOS. See the table below.

If a substring is known to match at end-of-line only, it may befollowed by $, as in floating 'k'$.

The optimizer-specific information is used to avoid entering (a slow) regexengine on strings that will not definitely match. If the isall flagis set, a call to the regex engine may be avoided even when the optimizerfound an appropriate place for the match.

Above the optimizer section is the list of nodes of the compiledform of the regex. Each line has format

id: TYPE OPTIONAL-INFO (next-id)

Types of Nodes

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 using native charset
 
 semantics for non-utf8
 
 BOUNDL no  Match "" at any locale word boundary
 
 BOUNDU no  Match "" at any word boundary using Unicode semantics
 
 BOUNDA no  Match "" at any word boundary using ASCII semantics
 
 NBOUND no  Match "" at any word non-boundary using native charset
 
 semantics for non-utf8
 
 NBOUNDL no  Match "" at any locale word non-boundary
 
 NBOUNDU no  Match "" at any word non-boundary using Unicode semantics
 
 NBOUNDA no  Match "" at any word non-boundary using ASCII semantics
 
 GPOS   no  Matches where last m//g left off.
 
 
 # [Special] alternatives:
 
 
 REG_ANY no  Match any one character (except newline).
 
 SANY   no  Match any one character.
 
 CANY   no  Match any one byte.
 
 ANYOF  sv  Match character in (or not in) this class, single char
 
 match only
 
 ANYOFV sv  Match character in (or not in) this class, can
 
 match-multiple chars
 
 ALNUM  no  Match any alphanumeric character using native charset
 
 semantics for non-utf8
 
 ALNUML no  Match any alphanumeric char in locale
 
 ALNUMU no  Match any alphanumeric char using Unicode semantics
 
 ALNUMA no  Match [A-Za-z_0-9]
 
 NALNUM no  Match any non-alphanumeric character using native charset
 
 semantics for non-utf8
 
 NALNUML no  Match any non-alphanumeric char in locale
 
 NALNUMU no  Match any non-alphanumeric char using Unicode semantics
 
 NALNUMA no  Match [^A-Za-z_0-9]
 
 SPACE  no  Match any whitespace character using native charset
 
 semantics for non-utf8
 
 SPACEL no  Match any whitespace char in locale
 
 SPACEU no  Match any whitespace char using Unicode semantics
 
 SPACEA no  Match [ \t\n\f\r]
 
 NSPACE no  Match any non-whitespace character using native charset
 
 semantics for non-utf8
 
 NSPACEL no  Match any non-whitespace char in locale
 
 NSPACEU no  Match any non-whitespace char using Unicode semantics
 
 NSPACEA no  Match [^ \t\n\f\r]
 
 DIGIT  no  Match any numeric character using native charset semantics
 
 for non-utf8
 
 DIGITL no  Match any numeric character in locale
 
 DIGITA no  Match [0-9]
 
 NDIGIT no  Match any non-numeric character using native charset
 
 i  semantics for non-utf8
 
 NDIGITL no  Match any non-numeric character in locale
 
 NDIGITA no  Match [^0-9]
 
 CLUMP  no  Match any extended grapheme cluster sequence
 
 
 # Alternation
 
 
 # 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.
 
 #
 
 BRANCHnode Match this alternative, or the next...
 
 
 # Back pointer
 
 
 # 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  str Match this string (preceded by length).
 
 EXACTF str Match this string, folded, native charset semantics for
 
 non-utf8 (prec. by length).
 
 EXACTFL str Match this string, folded in locale (w/len).
 
 EXACTFU str Match this string, folded, Unicode semantics for non-utf8
 
 (prec. by length).
 
 EXACTFA str Match this string, folded, Unicode semantics for non-utf8,
 
 but no ASCII-range character matches outside ASCII (prec.
 
 by length),.
 
 
 # Do nothing types
 
 
 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.
 
 
 # Loops
 
 
 # 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 Capture next-after-this simple thing
 
  CURLYM no 2 Capture 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.
 
 
  # Buffer related
 
 
  # 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 using native charset
 
  semantics for non-utf8
 
  REFFL  num 1   Match already matched string, folded in loc.
 
  REFFU  num 1   Match already matched string, folded using unicode
 
  semantics for non-utf8
 
  REFFA  num 1   Match already matched string, folded using unicode
 
  semantics for non-utf8, no mixing ASCII, non-ASCII
 
 
  # Named references.  Code in regcomp.c assumes that these all are after the
 
  # numbered references
 
  NREF   no-sv 1 Match some already matched string
 
  NREFF  no-sv 1 Match already matched string, folded using native charset
 
  semantics for non-utf8
 
  NREFFL no-sv 1 Match already matched string, folded in loc.
 
  NREFFU num   1 Match already matched string, folded using unicode
 
  semantics for non-utf8
 
  NREFFA num   1 Match already matched string, folded using unicode
 
  semantics for non-utf8, no mixing ASCII, non-ASCII
 
 
  IFMATCH off 1 2 Succeeds if the following matches.
 
  UNLESSM off 1 2 Fails if the following matches.
 
  SUSPEND off 1 1 "Independent" sub-RE.
 
  IFTHEN off 1 1 Switch, should be preceded by switcher.
 
  GROUPP num 1   Whether the group matched.
 
 
  # Support for long RE
 
 
  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.
 
 
  # Trie Related
 
 
  # Behave the same as A|LIST|OF|WORDS would. The '..C' variants have
 
  # inline charclass data (ascii only), the 'C' store it in the structure.
 
  # NOTE: the relative order of the TRIE-like regops  is significant
 
 
  TRIE   trie 1 Match many EXACT(F[ALU]?)? at once. flags==type
 
  TRIEC  charclass Same as TRIE, but with embedded charclass data
 
 
  # For start classes, contains an added fail table.
 
  AHOCORASICK trie 1   Aho Corasick stclass. flags==type
 
  AHOCORASICKC charclass Same as AHOCORASICK, but with embedded charclass data
 
 
  # Regex Subroutines
 
  GOSUB  num/ofs 2L recurse to paren arg1 at (signed) ofs arg2
 
  GOSTART no recurse to start of pattern
 
 
  # Special conditionals
 
  NGROUPP no-sv 1   Whether the group matched.
 
  INSUBP num 1 Whether we are in a specific recurse.
 
  DEFINEP none 1 Never execute directly.
 
 
  # Backtracking Verbs
 
  ENDLIKE none  Used only for the type field of verbs
 
  OPFAIL none  Same as (?!)
 
  ACCEPT parno 1   Accepts the current matched string.
 
 
 
  # Verbs With Arguments
 
  VERB   no-sv 1   Used only for the type field of verbs
 
  PRUNE  no-sv 1   Pattern fails at this startpoint if no-backtracking through this
 
  MARKPOINT  no-sv 1   Push the current location for rollback by cut.
 
  SKIP   no-sv 1   On failure skip forward (to the mark) before retrying
 
  COMMIT no-sv 1   Pattern fails outright if backtracking through this
 
  CUTGROUP   no-sv 1   On failure go to the next alternation in the group
 
 
  # Control what to keep in $&.
 
  KEEPS  no $& begins here.
 
 
  # New charclass like patterns
 
  LNBREAK none  generic newline pattern
 
  VERTWS none  vertical whitespace (Perl 6)
 
  NVERTWS none  not vertical whitespace (Perl 6)
 
  HORIZWS none  horizontal whitespace   (Perl 6)
 
  NHORIZWS   none  not horizontal whitespace   (Perl 6)
 
 
  FOLDCHAR   codepoint 1 codepoint with tricky case folding properties.
 
 
  # SPECIAL  REGOPS
 
 
  # 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.
 
 
  # Special opcode with the property that no opcode in a compiled program
 
  # will ever be of this type. Thus it can be used as a flag value that
 
  # no other opcode has been seen. END is used similarly, in that an END
 
  # node cant be optimized. So END implies "unoptimizable" and PSEUDO mean
 
  # "not seen anything to optimize yet".
 
  PSEUDO off   Pseudo opcode for internal use.
 

Following the optimizer information is a dump of the offset/lengthtable, 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 45entries. Each entry is a pair of integers, denoted by offset[length].Entries are numbered starting with 1, so entry #1 here is 1[4] andentry #12 is 5[1]. 1[4] indicates that the node labeled 1:(the 1: ANYOF[bc]) begins at character position 1 in thepre-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 thepre-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 thepre-compiled form of the regex, and has a length of 1 character---thatis, it corresponds to the + symbol in the precompiled regex.

0[0] items indicate that there is no corresponding node.

Run-time Output

First of all, when doing a match, one may get no run-time output evenif debugging is enabled. This means that the regex engine was neverentered 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 nodeof 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.

Debugging Perl Memory Usage

Perl is a profligate wastrel when it comes to memory use. Thereis a saying that to estimate memory usage of Perl, assume a reasonablealgorithm for memory allocation, multiply that estimate by 10, andwhile you still may miss the mark, at least you won't be quite soastonished. This is not absolutely true, but may provide a goodgrasp of what happens.

Assume that an integer cannot take less than 20 bytes of memory, afloat cannot take less than 24 bytes, a string cannot take lessthan 32 bytes (all these examples assume 32-bit architectures, theresult are quite a bit worse on 64-bit architectures). If a variableis accessed in two of three different ways (which require an integer,a float, or a string), the memory footprint may increase yet another20 bytes. A sloppy malloc(3) implementation can inflate thesenumbers dramatically.

On the opposite end of the scale, a declaration like

  sub foo;
 

may take up to 500 bytes of memory, depending on which release of Perlyou're running.

Anecdotal estimates of source-to-compiled code bloat suggest aneightfold increase. This means that the compiled form of reasonable(normally commented, properly indented etc.) code will takeabout eight times more space in memory than the code tookon disk.

The -DL command-line switch is obsolete since circa Perl 5.6.0(it was available only if Perl was built with -DDEBUGGING).The switch was used to track Perl's memory allocations and possiblememory leaks. These days the use of malloc debugging tools likePurify or valgrind is suggested instead. See alsoPERL_MEM_LOG in perlhacktips.

One way to find out how much memory is being used by Perl datastructures is to install the Devel::Size module from CPAN: it givesyou the minimum number of bytes required to store a particular datastructure. Please be mindful of the difference between the size()and total_size().

If Perl has been compiled using Perl's malloc you can analyze Perlmemory usage by setting $ENV{PERL_DEBUG_MSTATS}.

Using $ENV{PERL_DEBUG_MSTATS}

If your perl is using Perl's malloc() and was compiled with thenecessary switches (this is the default), then it will print memoryusage statistics after compiling your code when $ENV{PERL_DEBUG_MSTATS}> 1, and before termination of the program when $ENV{PERL_DEBUG_MSTATS} >= 1. The report format is similar tothe following example:

  $ PERL_DEBUG_MSTATS=2 perl -e "require Carp"
 
  Memory allocation statistics after compilation: (buckets 4(4)..8188(8192)
 
 14216 free:   130   117 28 7 9   0   2 2   1 0 0
 
437 61 36 0 5
 
 60924 used:   125   137   161 55 7   8   6 16   2 0 1
 
 74   109   304 84 20
 
  Total sbrk(): 77824/21:119. Odd ends: pad+heads+chain+tail: 0+636+0+2048.
 
  Memory allocation statistics after execution:   (buckets 4(4)..8188(8192)
 
 30888 free:   245 78 85 13 6   2   1 3   2 0 1
 
315   162 39 42 11
 
 175816 used:   265   176  1112   111 26  22  11 27   2 1 1
 
196   178  1066   798 39
 
  Total sbrk(): 215040/47:145. Odd ends: pad+heads+chain+tail: 0+2192+0+6144.
 

It is possible to ask for such a statistic at arbitrary points inyour execution using the mstat() function out of the standardDevel::Peek module.

Here is some explanation of that format:

• buckets SMALLEST(APPROX)..GREATEST(APPROX)

  Perl's malloc() uses bucketed allocations. Every request is roundedup to the closest bucket size available, and a bucket is taken fromthe pool of buckets of that size.

  The line above describes the limits of buckets currently in use.Each bucket has two sizes: memory footprint and the maximal sizeof user data that can fit into this bucket. Suppose in the aboveexample that the smallest bucket were size 4. The biggest bucketwould have usable size 8188, and the memory footprint would be 8192.

  In a Perl built for debugging, some buckets may have negative usablesize. This means that these buckets cannot (and will not) be used.For larger buckets, the memory footprint may be one page greaterthan a power of 2. If so, the corresponding power of two isprinted in the APPROX field above.

• Free/Used

  The 1 or 2 rows of numbers following that correspond to the numberof buckets of each size between SMALLEST and GREATEST. Inthe first row, the sizes (memory footprints) of buckets are powersof two--or possibly one page greater. In the second row, if present,the memory footprints of the buckets are between the memory footprintsof two buckets "above".

  For example, suppose under the previous example, the memory footprintswere

   free: 8 16 32 64 128  256 512 1024 2048 4096 8192
   
     4 12 24 48 80
   

  With a non-DEBUGGING perl, the buckets starting from 128 havea 4-byte overhead, and thus an 8192-long bucket may take up to8188-byte allocations.

• Total sbrk(): SBRKed/SBRKs:CONTINUOUS

  The first two fields give the total amount of memory perl sbrk(2)ed(ess-broken? :-) and number of sbrk(2)s used. The third number iswhat perl thinks about continuity of returned chunks. So long asthis number is positive, malloc() will assume that it is probablethat sbrk(2) will provide continuous memory.

  Memory allocated by external libraries is not counted.

• pad: 0

  The amount of sbrk(2)ed memory needed to keep buckets aligned.

• heads: 2192

  Although memory overhead of bigger buckets is kept inside the bucket, forsmaller buckets, it is kept in separate areas. This field gives thetotal size of these areas.

• chain: 0

  malloc() may want to subdivide a bigger bucket into smaller buckets.If only a part of the deceased bucket is left unsubdivided, the restis kept as an element of a linked list. This field gives the totalsize of these chunks.

• tail: 6144

  To minimize the number of sbrk(2)s, malloc() asks for more memory. Thisfield gives the size of the yet unused part, which is sbrk(2)ed, butnever touched.

SEE ALSO

perldebug,perlguts,perlrunre,andDevel::DProf.