X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/6d0f518e0b7ff19ca6956aba9c075bcc87b59d84..c9da69fb2cff080fa286bf64ac1d12f81bab3bf6:/pod/perldebug.pod diff --git a/pod/perldebug.pod b/pod/perldebug.pod index 2431fc4..2e21941 100644 --- a/pod/perldebug.pod +++ b/pod/perldebug.pod @@ -1,4 +1,5 @@ =head1 NAME +X X perldebug - Perl debugging @@ -6,16 +7,11 @@ perldebug - Perl debugging First of all, have you tried using the B<-w> switch? -=head1 The Perl 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 new to the Perl debugger, you may prefer to read +L, which is a tutorial introduction to the debugger . -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 +20,16 @@ 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 @@ -41,12 +38,21 @@ 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.) - -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. +(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 Debugger Commands @@ -54,88 +60,123 @@ The 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<"Configurable Options">. -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. - -Nested data structures are printed out in a legible fashion, unlike -the C function. +Use C<~pattern> and C for positive and negative regexes. -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. @@ -145,7 +186,7 @@ List C lines starting at C. =item l min-max -List lines C through C. C> is synonymous to C>. +List lines C through C. C is synonymous to C<->. =item l line @@ -154,134 +195,133 @@ List a single line. =item l subname List first window of lines from subroutine. I may -be a variable which contains a code reference. +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 eval statement. If C -is not a full filename as found in values of %INC, it is considered as -a regexp. +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. 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 currently executed C -and of Ced strings which define subroutines are saved, thus are -accessible by this mechanism. +(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 +X -Toggle trace mode (see also C Cption). +Toggle trace mode (see also the C option). =item t expr +X -Trace through execution of expr. For example: - - $ 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 } +Trace through execution of C. +See L for examples. - DB<3> t print foo() * bar() - main::((eval 172):3): print foo() + bar(); - main::foo((eval 168):2): - main::bar((eval 170):2): - 42 +=item b +X +X -or, with the Cption C 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 +Sets breakpoint on current line =item b [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. 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 =item b subname [condition] +X +X -Set a breakpoint at the first line of the named subroutine. I may -be a variable which contains a code reference (in this case I +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 +X -Set an action to be done before the line is executed. +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 1. check for a breakpoint at this line @@ -295,92 +335,375 @@ For example, this will print out $foo every time line a 53 print "DB FOUND $foo\n" -=item A +=item A line +X + +Delete an action from the specified line. + +=item A * +X Delete all installed actions. -=item W [expr] +=item w expr +X -Add a global watch-expression. +Add a global watch-expression. We hope you know what one of these +is, because they're supposed to be obvious. -=item W +=item W expr +X + +Delete watch-expression + +=item W * +X Delete all watch-expressions. -=item O [opt[=val]] [opt"val"] [opt?]... +=item o +X + +Display all options + +=item o booloption ... +X + +Set each listed Boolean option to the value C<1>. + +=item o anyoption? ... +X + +Print out the value of one or more options. + +=item o option=value ... +X + +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. + +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