X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/c2611fb358d57faaf2390cf4e8c5224abf2c4cc4..c2bb91f92aafd4647235159d54064fad237aa7b1:/pod/perldebug.pod diff --git a/pod/perldebug.pod b/pod/perldebug.pod index 760d517..53c3d60 100644 --- a/pod/perldebug.pod +++ b/pod/perldebug.pod @@ -1,21 +1,20 @@ =head1 NAME +X X perldebug - Perl debugging =head1 DESCRIPTION -First of all, have you tried using the B<-w> switch? +First of all, have you tried using L|strict> and +L|warnings>? -=head1 The Perl Debugger +If you're new to the Perl debugger, you may prefer to read +L, which is a tutorial introduction to the debugger. -"As soon as we started programming, we found to our -surprise that it wasn't as easy to get programs right -as we had thought. Debugging had to be discovered. -I can remember the exact instant when I realized that -a large part of my life from then on was going to be -spent in finding mistakes in my own programs." +If you're looking for the nitty gritty details of how the debugger is +I, you may prefer to read L. -I< --Maurice Wilkes, 1949> +=head1 The Perl Debugger If you invoke Perl with the B<-d> switch, your script runs under the Perl source debugger. This works like an interactive Perl @@ -24,15 +23,16 @@ source code, set breakpoints, get stack backtraces, change the values of variables, etc. This is so convenient that you often fire up the debugger all by itself just to test out Perl constructs interactively to see what they do. For example: +X<-d> - perl -d -e 42 + $ perl -d -e 42 -In Perl, the debugger is not a separate program as it usually is in the +In Perl, the debugger is not a separate program the way it usually is in the typical compiled environment. Instead, the B<-d> flag tells the compiler to insert source information into the parse trees it's about to hand off to the interpreter. That means your code must first compile correctly for the debugger to work on it. Then when the interpreter starts up, it -preloads a Perl library file containing the debugger itself. +preloads a special Perl library file containing the debugger. The program will halt I the first run-time executable statement (but see below regarding compile-time statements) and ask you @@ -41,101 +41,168 @@ the debugger halts and shows you a line of code, it always displays the line it's I to execute, rather than the one it has just executed. Any command not recognized by the debugger is directly executed -(C'd) as Perl code in the current package. (The debugger uses the -DB package for its own state information.) +(C'd) as Perl code in the current package. (The debugger +uses the DB package for keeping its own state information.) + +Note that the said C is bound by an implicit scope. As a +result any newly introduced lexical variable or any modified +capture buffer content is lost after the eval. The debugger is a +nice environment to learn Perl, but if you interactively experiment using +material which should be in the same scope, stuff it in one line. + +For any text entered at the debugger prompt, leading and trailing whitespace +is first stripped before further processing. If a debugger command +coincides with some function in your own program, merely precede the +function with something that doesn't look like a debugger command, such +as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses +or braces. + +=head2 Calling the Debugger + +There are several ways to call the debugger: + +=over 4 + +=item perl -d program_name + +On the given program identified by C. + +=item perl -d -e 0 + +Interactively supply an arbitrary C using C<-e>. -Leading white space before a command would cause the debugger to think -it's I a debugger command but for Perl, so be careful not to do -that. +=item perl -d:ptkdb program_name + +Debug a given program via the C GUI. + +=item perl -dt threaded_program_name + +Debug a given program using threads (experimental). + +=back =head2 Debugger Commands -The debugger understands the following commands: +The interactive debugger understands the following commands: =over 12 +=item h +X + +Prints out a summary help message + =item h [command] -Prints out a help message. +Prints out a help message for the given debugger command. + +=item h h -If you supply another debugger command as an argument to the C command, -it prints out the description for just that command. The special -argument of C produces a more compact help listing, designed to fit -together on one screen. +The special argument of C produces the entire help page, which is quite long. -If the output of the C command (or any command, for that matter) scrolls -past your screen, either precede the command with a leading pipe symbol so -it's run through your pager, as in +If the output of the C command (or any command, for that matter) scrolls +past your screen, precede the command with a leading pipe symbol so +that it's run through your pager, as in - DB> |h + DB> |h h -You may change the pager which is used via C command. +You may change the pager which is used via C command. =item p expr +X Same as C in the current package. In particular, -because this is just Perl's own B function, this means that nested +because this is just Perl's own C function, this means that nested data structures and objects are not dumped, unlike with the C command. The C filehandle is opened to F, regardless of where STDOUT may be redirected to. -=item x expr +=item x [maxdepth] expr +X + +Evaluates its expression in list context and dumps out the result in a +pretty-printed fashion. Nested data structures are printed out +recursively, unlike the real C function in Perl. When dumping +hashes, you'll probably prefer 'x \%h' rather than 'x %h'. +See L if you'd like to do this yourself. -Evaluates its expression in list context and dumps out the result -in a pretty-printed fashion. Nested data structures are printed out -recursively, unlike the C function. +The output format is governed by multiple options described under +L. -The details of printout are governed by multiple Cptions. +If the C is included, it must be a numeral I; the value is +dumped only I levels deep, as if the C option had been +temporarily set to I. =item V [pkg [vars]] +X -Display all (or some) variables in package (defaulting to the C
-package) using a data pretty-printer (hashes show their keys and values so -you see what's what, control characters are made printable, etc.). Make -sure you don't put the type specifier (like C<$>) there, just the symbol -names, like this: +Display all (or some) variables in package (defaulting to C
) +using a data pretty-printer (hashes show their keys and values so +you see what's what, control characters are made printable, etc.). +Make sure you don't put the type specifier (like C<$>) there, just +the symbol names, like this: V DB filename line -Use C<~pattern> and C for positive and negative regexps. +Use C<~pattern> and C for positive and negative regexes. -Nested data structures are printed out in a legible fashion, unlike -the C function. - -The details of printout are governed by multiple Cptions. +This is similar to calling the C command on each applicable var. =item X [vars] +X Same as C. +=item y [level [vars]] +X + +Display all (or some) lexical variables (mnemonic: C variables) +in the current scope or I scopes higher. You can limit the +variables that you see with I which works exactly as it does +for the C and C commands. Requires the C module +version 0.08 or higher; will warn if this isn't installed. Output +is pretty-printed in the same style as for C and the format is +controlled by the same options. + =item T +X X X Produce a stack backtrace. See below for details on its output. =item s [expr] +X X -Single step. Executes until it reaches the beginning of another +Single step. Executes until the beginning of another statement, descending into subroutine calls. If an expression is supplied that includes function calls, it too will be single-stepped. =item n [expr] +X -Next. Executes over subroutine calls, until it reaches the beginning +Next. Executes over subroutine calls, until the beginning of the next statement. If an expression is supplied that includes function calls, those functions will be executed with stops before each statement. -=item ECRE +=item r +X + +Continue until the return from the current subroutine. +Dump the return value if the C option is set (default). + +=item Repeat last C or C command. =item c [line|sub] +X Continue, optionally inserting a one-time-only breakpoint at the specified line or subroutine. =item l +X List next window of lines. @@ -153,436 +220,410 @@ List a single line. =item l subname -List first window of lines from subroutine. +List first window of lines from subroutine. I may +be a variable that contains a code reference. =item - +X List previous window of lines. -=item w [line] +=item v [line] +X -List window (a few lines) around the current line. +View a few lines of code around the current line. =item . +X -Return debugger pointer to the last-executed line and -print it out. +Return the internal debugger pointer to the line last +executed, and print out that line. =item f filename +X + +Switch to viewing a different file or C statement. If I +is not a full pathname found in the values of %INC, it is considered +a regex. -Switch to viewing a different file or eval statement. If C -is not a full filename as found in values of %INC, it is considered as -a regexp. +Ced strings (when accessible) are considered to be filenames: +C and C access the body of the 7th Ced string +(in the order of execution). The bodies of the currently executed C +and of Ced strings that define subroutines are saved and thus +accessible. =item /pattern/ -Search forwards for pattern; final / is optional. +Search forwards for pattern (a Perl regex); final / is optional. +The search is case-insensitive by default. =item ?pattern? Search backwards for pattern; final ? is optional. +The search is case-insensitive by default. -=item L +=item L [abw] +X -List all breakpoints and actions. +List (default all) actions, breakpoints and watch expressions -=item S [[!]pattern] +=item S [[!]regex] +X -List subroutine names [not] matching pattern. +List subroutine names [not] matching the regex. -=item t +=item t [n] +X -Toggle trace mode (see also C Cption). +Toggle trace mode (see also the C option). +Optional argument is the maximum number of levels to trace below +the current one; anything deeper than that will be silent. -=item t expr +=item t [n] expr +X -Trace through execution of expr. For example: +Trace through execution of C. +Optional first argument is the maximum number of levels to trace below +the current one; anything deeper than that will be silent. +See L for examples. - $ perl -de 42 - Stack dump during die enabled outside of evals. +=item b +X +X - Loading DB routines from perl5db.pl patch level 0.94 - Emacs support available. +Sets breakpoint on current line - Enter h or `h h' for help. - - main::(-e:1): 0 - DB<1> sub foo { 14 } +=item b [line] [condition] +X +X - DB<2> sub bar { 3 } +Set a breakpoint before the given line. If a condition +is specified, it's evaluated each time the statement is reached: a +breakpoint is taken only if the condition is true. Breakpoints may +only be set on lines that begin an executable statement. Conditions +don't use C: - DB<3> t print foo() * bar() - main::((eval 172):3): print foo() + bar(); - main::foo((eval 168):2): - main::bar((eval 170):2): - 42 + b 237 $x > 30 + b 237 ++$count237 < 11 + b 33 /pattern/i -or, with the Cption C set, +If the line number is C<.>, sets a breakpoint on the current line: - 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 + b . $n > 100 -=item b [line] [condition] +=item b [file]:[line] [condition] +X +X -Set a breakpoint. If line is omitted, sets a breakpoint on the line -that is about to be executed. If a condition is specified, it's -evaluated each time the statement is reached and a breakpoint is taken -only if the condition is true. Breakpoints may be set on only lines -that begin an executable statement. Conditions don't use B: +Set a breakpoint before the given line in a (possibly different) file. If a +condition is specified, it's evaluated each time the statement is reached: a +breakpoint is taken only if the condition is true. Breakpoints may only be set +on lines that begin an executable statement. Conditions don't use C: - b 237 $x > 30 - b 237 ++$count237 < 11 - b 33 /pattern/i + b lib/MyModule.pm:237 $x > 30 + b /usr/lib/perl5/site_perl/CGI.pm:100 ++$count100 < 11 =item b subname [condition] +X +X -Set a breakpoint at the first line of the named subroutine. +Set a breakpoint before the first line of the named subroutine. I may +be a variable containing a code reference (in this case I +is not supported). =item b postpone subname [condition] +X +X -Set breakpoint at first line of subroutine after it is compiled. +Set a breakpoint at first line of subroutine after it is compiled. =item b load filename +X +X -Set breakpoint at the first executed line of the file. Filename should -be a full name as found in values of %INC. +Set a breakpoint before the first executed line of the I, +which should be a full pathname found amongst the %INC values. =item b compile subname +X +X -Sets breakpoint at the first statement executed after the subroutine -is compiled. +Sets a breakpoint before the first statement executed after the specified +subroutine is compiled. -=item d [line] +=item B line +X +X -Delete a breakpoint at the specified line. If line is omitted, deletes -the breakpoint on the line that is about to be executed. +Delete a breakpoint from the specified I. -=item D +=item B * +X +X Delete all installed breakpoints. -=item a [line] command - -Set an action to be done before the line is executed. -The sequence of steps taken by the debugger is - - 1. check for a breakpoint at this line - 2. print the line if necessary (tracing) - 3. do any actions associated with that line - 4. prompt user if at a breakpoint or in single-step - 5. evaluate line - -For example, this will print out $foo every time line -53 is passed: - - a 53 print "DB FOUND $foo\n" - -=item A - -Delete all installed actions. - -=item W [expr] - -Add a global watch-expression. - -=item W - -Delete all watch-expressions. - -=item O [opt[=val]] [opt"val"] [opt?]... - -Set or query values of options. val defaults to 1. opt can -be abbreviated. Several options can be listed. - -=over 12 - -=item C, C - -The characters used to recall command or spawn shell. By -default, these are both set to C. - -=item C - -Program to use for output of pager-piped commands (those -beginning with a C<|> character.) By default, -C<$ENV{PAGER}> will be used. - -=item C - -Run Tk while prompting (with ReadLine). - -=item C, C, C - -Level of verbosity. By default the debugger is in a sane verbose mode, -thus it will print backtraces on all the warnings and die-messages -which are going to be printed out, and will print a message when -interesting uncaught signals arrive. - -To disable this behaviour, set these values to 0. If C is 2, -then the messages which will be caught by surrounding C are also -printed. - -=item C - -Trace mode (similar to C command, but can be put into -C). - -=item C - -File or pipe to print line number info to. If it is a pipe (say, -C<|visual_perl_db>), then a short, "emacs like" message is used. - -=item C - -If 0, allows I the end of the script. - -=item C - -affects printing of return value after C command. - -=item C - -affects screen appearance of the command line (see L). - -=item C - -affects printing messages on entry and exit from subroutines. If -C is false, messages are printed on entry only. (Printing -on exit may be useful if inter(di)spersed with other messages.) - -If C, arguments to functions are printed as well as the -context and caller info. If C, overloaded C and -Cd C are enabled on the printed arguments. If C, the return value from the subroutine is printed as well. - -The length at which the argument list is truncated is governed by the -next option: - -=item C - -length at which the argument list is truncated when C option's -bit 4 is set. - -=back - -The following options affect what happens with C, C, and C -commands: - -=over 12 - -=item C, C - -Print only first N elements ('' for all). - -=item C, C +=item disable [file]:[line] +X +X +X -Change style of array and hash dump. If C, short array -may be printed on one line. - -=item C +Disable the breakpoint so it won't stop the execution of the program. +Breakpoints are enabled by default and can be re-enabled using the C +command. -Whether to print contents of globs. +=item disable [line] +X +X +X -=item C +Disable the breakpoint so it won't stop the execution of the program. +Breakpoints are enabled by default and can be re-enabled using the C +command. -Dump arrays holding debugged files. +This is done for a breakpoint in the current file. -=item C +=item enable [file]:[line] +X +X +X -Dump symbol tables of packages. +Enable the breakpoint so it will stop the execution of the program. -=item C +=item enable [line] +X +X +X -Dump contents of "reused" addresses. +Enable the breakpoint so it will stop the execution of the program. -=item C, C, C +This is done for a breakpoint in the current file. -Change style of string dump. Default value of C is C, one -can enable either double-quotish dump, or single-quotish by setting it -to C<"> or C<'>. By default, characters with high bit set are printed -I. +=item a [line] command +X -=item C +Set an action to be done before the line is executed. If I is +omitted, set an action on the line about to be executed. +The sequence of steps taken by the debugger is -I rudimentally per-package memory usage dump. Calculates total -size of strings in variables in the package. + 1. check for a breakpoint at this line + 2. print the line if necessary (tracing) + 3. do any actions associated with that line + 4. prompt user if at a breakpoint or in single-step + 5. evaluate line -=back +For example, this will print out $foo every time line +53 is passed: -During startup options are initialized from C<$ENV{PERLDB_OPTS}>. -You can put additional initialization options C, C, -C, and C there. + a 53 print "DB FOUND $foo\n" -Example rc file: +=item A line +X - &parse_options("NonStop=1 LineInfo=db.out AutoTrace"); +Delete an action from the specified line. -The script will run without human intervention, putting trace information -into the file I. (If you interrupt it, you would better reset -C to something "interactive"!) +=item A * +X -=over 12 +Delete all installed actions. -=item C +=item w expr +X -The TTY to use for debugging I/O. +Add a global watch-expression. Whenever a watched global changes the +debugger will stop and display the old and new values. -=item C +=item W expr +X -If set, goes in C mode, and would not connect to a TTY. If -interrupt (or if control goes to debugger via explicit setting of -$DB::signal or $DB::single from the Perl script), connects to a TTY -specified by the C option at startup, or to a TTY found at -runtime using C module of your choice. +Delete watch-expression -This module should implement a method C which returns an object -with two methods: C and C, returning two filehandles to use -for debugging input and output correspondingly. Method C may -inspect an argument which is a value of C<$ENV{PERLDB_NOTTY}> at -startup, or is C<"/tmp/perldbtty$$"> otherwise. +=item W * +X -=item C +Delete all watch-expressions. -If false, readline support in debugger is disabled, so you can debug -ReadLine applications. +=item o +X -=item C +Display all options. -If set, debugger goes into noninteractive mode until interrupted, or -programmatically by setting $DB::signal or $DB::single. +=item o booloption ... +X -=back +Set each listed Boolean option to the value C<1>. -Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: +=item o anyoption? ... +X - $ PERLDB_OPTS="N f=2" perl -d myprogram +Print out the value of one or more options. -will run the script C without human intervention, printing -out the call tree with entry and exit points. Note that C is -equivalent to C. Note also that at the moment when -this documentation was written all the options to the debugger could -be uniquely abbreviated by the first letter (with exception of -C options). +=item o option=value ... +X -Other examples may include +Set the value of one or more options. If the value has internal +whitespace, it should be quoted. For example, you could set C to call B with those specific options. +You may use either single or double quotes, but if you do, you must +escape any embedded instances of same sort of quote you began with, +as well as any escaping any escapes that immediately precede that +quote but which are not meant to escape the quote itself. In other +words, you follow single-quoting rules irrespective of the quote; +eg: C or C. - $ PERLDB_OPTS="N f A L=listing" perl -d myprogram +For historical reasons, the C<=value> is optional, but defaults to +1 only where it is safe to do so--that is, mostly for Boolean +options. It is always better to assign a specific value using C<=>. +The C