X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperldebguts.pod;h=f507ac8997a72a12e3cfc9a37d0ffea55fa0cef9;hb=aa92477d39232c1f4aabd6cccf539401dbada72b;hp=827bb2f7d0f4fb7696e80201a468c283adffb56d;hpb=fe854a6f990f7776a8ee8bd28f02e1bd36e5bb58;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perldebguts.pod b/pod/perldebguts.pod index 827bb2f..f507ac8 100644 --- a/pod/perldebguts.pod +++ b/pod/perldebguts.pod @@ -5,9 +5,10 @@ perldebguts - Guts of Perl debugging =head1 DESCRIPTION This is not the perldebug(1) manpage, which tells you how to use -the debugger. This manpage describes low-level details ranging -between difficult and impossible for anyone who isn't incredibly -intimate with Perl's guts to understand. Caveat lector. +the debugger. This manpage describes low-level details concerning +the debugger's internals, which range from difficult to impossible +to understand for anyone who isn't incredibly intimate with Perl's guts. +Caveat lector. =head1 Debugger Internals @@ -18,10 +19,11 @@ usable only if a special Perl is built per the instructions in the F podpage in the Perl source tree. For example, whenever you call Perl's built-in C function -from the package DB, the arguments that the corresponding stack -frame was called with are copied to the @DB::args array. The -general mechanisms is enabled by calling Perl with the B<-d> switch, the -following additional features are enabled (cf. L): +from the package C, the arguments that the corresponding stack +frame was called with are copied to the C<@DB::args> array. These +mechanisms are enabled by calling Perl with the B<-d> switch. +Specifically, the following additional features are enabled +(cf. L): =over 4 @@ -33,10 +35,10 @@ Perl inserts the contents of C<$ENV{PERL5DB}> (or C holds the lines of $filename for a -file compiled by Perl. The same for Ced strings that contain -subroutines, or which are currently being executed. The $filename -for Ced strings looks like C<(eval 34)>. Code assertions -in regexes look like C<(re_eval 19)>. +file compiled by Perl. The same is also true for Ced strings +that contain subroutines, or which are currently being executed. +The $filename for Ced strings looks like C<(eval 34)>. +Code assertions in regexes look like C<(re_eval 19)>. Values in this array are magical in numeric context: they compare equal to zero only if the line is not breakable. @@ -84,8 +86,8 @@ Cs, or C<(re_eval 19)> for those within regex code assertions. =item * When the execution of your program reaches a point that can hold a -breakpoint, the C subroutine is called any of the variables -$DB::trace, $DB::single, or $DB::signal is true. These variables +breakpoint, the C subroutine is called if any of the variables +C<$DB::trace>, C<$DB::single>, or C<$DB::signal> is true. These variables are not Cizable. This feature is disabled when executing inside C, including functions called from it unless C<< $^D & (1<<30) >> is true. @@ -94,77 +96,122 @@ unless C<< $^D & (1<<30) >> is true. When execution of the program reaches a subroutine call, a call to C<&DB::sub>(I) is made instead, with C<$DB::sub> holding the -name of the called subroutine. This doesn't happen if the subroutine +name of the called subroutine. (This doesn't happen if the subroutine was compiled in the C package.) =back Note that if C<&DB::sub> needs external data for it to work, no -subroutine call is possible until this is done. For the standard -debugger, the C<$DB::deep> variable (how many levels of recursion -deep into the debugger you can go before a mandatory break) gives -an example of such a dependency. +subroutine call is possible without it. As an example, the standard +debugger's C<&DB::sub> depends on the C<$DB::deep> variable +(it defines how many levels of recursion deep into the debugger you can go +before a mandatory break). If C<$DB::deep> is not defined, subroutine +calls are not possible, even though C<&DB::sub> exists. =head2 Writing Your Own Debugger -The minimal working debugger consists of one line - +=head3 Environment Variables + +The C 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 {} -which is quite handy as contents of C environment -variable: - +It can easily be defined like this: + $ PERL5DB="sub DB::DB {}" perl -d your-script -Another brief debugger, slightly more useful, could be created +Another brief debugger, slightly more useful, can be created with only the line: sub DB::DB {print ++$i; scalar } -This debugger would print the sequential number of encountered -statement, and would wait for you to hit a newline before continuing. - -The following debugger is quite functional: - +This debugger prints a number which increments for each statement +encountered and waits for you to hit a newline before continuing +to the next statement. + +The following debugger is actually useful: + { package DB; sub DB {} sub sub {print ++$i, " $sub\n"; &$sub} } -It prints the sequential number of subroutine call and the name of the -called subroutine. Note that C<&DB::sub> should be compiled into the -package C. +It prints the sequence number of each subroutine call and the name of the +called subroutine. Note that C<&DB::sub> is being compiled into the +package C through the use of the C directive. -At the start, the debugger reads your rc file (F<./.perldb> or -F<~/.perldb> under Unix), which can set important options. This file may -define a subroutine C<&afterinit> to be executed after the debugger is -initialized. +When it starts, the debugger reads your rc file (F<./.perldb> or +F<~/.perldb> under Unix), which can set important options. +(A subroutine (C<&afterinit>) can be defined here as well; it is executed +after the debugger completes its own initialization.) After the rc file is read, the debugger reads the PERLDB_OPTS -environment variable and parses this as the remainder of a C -line as one might enter at the debugger prompt. +environment variable and uses it to set debugger options. The +contents of this variable are treated as if they were the argument +of an C debugger command (q.v. in L). + +=head3 Debugger internal variables +In addition to the file and subroutine-related variables mentioned above, +the debugger also maintains various magical internal variables. + +=over 4 + +=item * -The debugger also maintains magical internal variables, such as -C<@DB::dbline>, C<%DB::dbline>, which are aliases for -C<@{"::_ C<%{"::_. Here C -is the currently selected file, either explicitly chosen with the +C<@DB::dbline> is an alias for C<@{"::_, which +holds the lines of the currently-selected file (compiled by Perl), either +explicitly chosen with the debugger's C command, or implicitly by flow +of execution. + +Values in this array are magical in numeric context: they compare +equal to zero only if the line is not breakable. + +=item * + +C<%DB::dbline>, is an alias for C<%{"::_, which +contains breakpoints and actions keyed by line number in +the currently-selected file, either explicitly chosen with the debugger's C command, or implicitly by flow of execution. -Some functions are provided to simplify customization. See -L for description of options parsed by -C. The function C skips the specified number of frames and returns a list -containing information about the calling frames (all of them, if -C is missing). Each entry is reference to a hash with -keys C (either C<.>, C<$>, or C<@>), C (subroutine +As previously noted, individual entries (as opposed to the whole hash) +are settable. Perl only cares about Boolean true here, although +the values used by F have the form +C<"$break_condition\0$action">. + +=back + +=head3 Debugger customization functions + +Some functions are provided to simplify customization. + +=over 4 + +=item * + +See L for description of options parsed by +C parses debugger options; see +L for a description of options recognized. + +=item * + +C skips the specified number of frames +and returns a list containing information about the calling frames (all +of them, if C is missing). Each entry is reference to a hash +with keys C (either C<.>, C<$>, or C<@>), C (subroutine name, or info about C), C (C or a reference to an array), C, and C. -The function C prints +=item * + +C prints formatted info about caller frames. The last two functions may be convenient as arguments to C<< < >>, C<< << >> commands. +=back + Note that any variables and functions that are not documented in this manpages (or in L) are considered for internal use only, and as such are subject to change without notice. @@ -193,9 +240,9 @@ information. For example, contrast this expression trace: main::bar((eval 170):2): 42 -with this one, once the Cption C has been set: +with this one, once the Cption C has been set: - DB<4> O f=2 + DB<4> o f=2 frame = '2' DB<5> t print foo() * bar() 3: foo() * bar()