Devel::Trepan -- A new modular Perl debugger
A modular, testable, gdb-like debugger in the family of the Ruby trepanning debuggers.
extensive online-help
syntax highlighting of Perl code
context-sensitive command completion
out-of-process and remote debugging
interactive shell support
code disassembly
gdb syntax
easy extensibility at several levels: aliases, commands, and plugins
comes with extensive tests
is not as ugly as perl5db
Some of the features above require additional modules before they take effect. See "Plugins" and "Recommended Modules" below.
From a shell:
$ trepan.pl [trepan-opts] -- perl-program [perl-program-opts]
For out-of-process (and possibly out-of server) debugging:
$ trepan.pl --server [trepan-opts] -- perl-program [perl-program-opts]
and then from another process or computer:
$ trepan.pl --client [--host DNS-NAME-OR-IP]
Calling the debugger from inside your Perl program using Joshua ben Jore's Enbugger:
# This needs to be done once and could even be in some sort of # conditional code require Enbugger; Enbugger->load_debugger( 'trepan' ); # Alternatively, to unconditionally load Enbugger and trepan: use Enbugger 'trepan'; # work, work, work... # Oops! there was an error! Enable the debugger now! Enbugger->stop; # or Enbugger->stop if ...
Or if you just want POSIX-shell-like set -x line tracing:
set -x
$ trepan.pl -x -- perl-program [perl-program-opts]
Inside the debugger tracing is turned on using the command set trace print. There is extensive help from the help command.
set trace print
help
The help system follows the gdb classificiation. Below is not a full list of commands, nor does it contain the full list of options on each command, but rather some of the more basic commands and options.
"Commands involving running the program"
"Examining data"
"Making the program stop at certain points"
"Examining the call stack"
"Support facilities"
"Syntax of debugger commands"
The commands in the section involve controlling execution of the program, either by kinds of stepping (step into, step over, step out) restarting or termintating the program altogether. However setting breakpoints is in "Making the program stop at certain points".
"Step into (step)"
"Step over (next)"
"Continue execution (continue)"
"Step out (finish)"
"Gently exit debugged program (quit)"
"Hard termination (kill)"
"Restart execution (restart)"
step[<+|-] [into] [count]
Execute the current line, stopping at the next event. Sometimes this is called "step into".
With an integer argument, step that many times. With an 'until' expression that expression is evaluated and we stop the first time it is true.
A suffix of + in a command or an alias forces a move to another position, while a suffix of - disables this requirement. A suffix of > will continue until the next call. (finish will run run until the return for that call.)
+
-
>
finish
If no suffix is given, the debugger setting different determines this behavior.
different
Examples:
step # step 1 event, *any* event obeying 'set different' setting step 1 # same as above step+ # same but force stopping on a new line step over # same as 'next' step out # same as 'finish'
Related and similar is the next (step over) and finish (step out) commands. All of these are slower than running to a breakpoint.
next
Step one statement ignoring steps into function calls at this level. Sometimes this is called "step over".
continue [location]
Leave the debugger loop and continue execution. Subsequent entry to the debugger however may occur via breakpoints or explicit calls, or exceptions.
If a parameter is given, a temporary breakpoint is set at that position before continuing.
continue continue 10 # continue to line 10 continue gcd # continue to first instruction of method gcd
See also step, next, finish commands and help location.
step
help location
Continue execution until the program is about to leave the current function. Sometimes this is called 'step out'.
quit[!] [unconditionally] [exit-code]
Gently exit the debugger and debugged program.
The program being debugged is exited via exit() which runs the Kernel at_exit() finalizers. If a return code is given, that is the return code passed to exit() - presumably the return code that will be passed back to the OS. If no exit code is given, 0 is used.
quit # quit prompting if we are interactive quit unconditionally # quit without prompting quit! # same as above quit 0 # same as "quit" quit! 1 # unconditional quit setting exit code 1
See also set confirm and kill.
set confirm
kill
kill[!] [signal-number|signal-name]
Kill execution of program being debugged.
Equivalent of kill('KILL', $$). This is an unmaskable signal. Use this when all else fails, e.g. in thread code, use this.
kill('KILL', $$)
If you are in interactive mode, you are prompted to confirm killing. However when this command is aliased from a command ending in !, no questions are asked.
!
kill kill KILL # same as above kill -9 # same as above kill 9 # same as above kill! 9 # same as above, but no questions asked kill unconditionally # same as above kill TERM # Send "TERM" signal
See also quit
quit
restart
Restart debugger and program via an exec call.
See also show args for the exact invocation that will be used.
show args
"Evaluate Perl code (eval)"
"Recursively Debug into Perl code"
eval[@$][?] [Perl-code]
Run Perl-code in the context of the current frame.
If no string is given after the word "eval", we run the string from the current source code about to be run. If the "eval" command ends ? (via an alias) and no string is given we try to pick out a useful expression in the line.
Normally eval assumes you are typing a statement, not an expression; the result is a scalar value. However you can force the type of the result by adding the appropriate sigil @, or $.
@
$
eval 1+2 # 3 eval$ 3 # Same as above, but the return type is explicit $ 3 # Probably same as above if $ alias is around eval $^X # Possibly /usr/bin/perl eval # Run current source-code line eval? # but strips off leading 'if', 'while', .. # from command eval @ARGV # Make sure the result saved is an array rather than # an array converted to a scalar. @ @ARG # Same as above if @ alias is around use English # Note this is a statement, not an expression use English; # Same as above eval$ use English # Error because this is not a valid expression
See also set auto eval to treat unrecognized debugger commands as Perl code.
set auto eval
debug Perl-code
Recursively debug Perl-code.
The level of recursive debugging is shown in the prompt. For example ((trepan.pl)) indicates one nested level of debugging.
((trepan.pl))
debug finonacci(5) # Debug fibonacci function debug $x=1; $y=2; # Kind of pointless, but doable.
A Breakpoint is a way to have the program stop at a pre-determined location. A breakpoint can be perminant or one-time. A one-time breakpoint is removed as soon as it is hit. In a sense, stepping is like setting one-time breakpoints. Breakpoints can also be disabled which allows you to temporarily ignore stopping at that breakpoint while it is disabled. Finally one can control conditions under which a breakpoint is enacted upon.
Another way to force a stop is to watch to see if the value of an expression changes. Often that expression is simply examinging a variable's value.
"Set a breakpoint (break)"
"Set a temporary breakpoint (tbreak)"
"Add or modify a condition on a breakpoint (condition)"
"Delete some breakpoints (delete)"
"Enable some breakpoints (enable)"
"Disable some breakpoints (disable)"
"Set an action before a line is executed (action)"
"Stop when an expression changes value (watch)"
break [location] [if condition]
Set a breakpoint. If location is given use the current stopping point. An optional condition may be given.
break # set a breakpoint on the current line break gcd # set a breakpoint in function gcd break gcd if $a == 1 # set a breakpoint in function gcd with # condition $a == 1 break 10 # set breakpoint on line 10
When a breakpoint is hit the event icon is xx.
xx
See also help breakpoints.
help breakpoints
tbreak [location]
Set a one-time breakpoint. The breakpoint is removed after it is hit. If no location is given use the current stopping point.
tbreak tbreak 10 # set breakpoint on line 10
When a breakpoint is hit the event icon is x1.
x1
See also break and help breakpoints.
break
condition bp-number Perl-expression
bp-number is a breakpoint number. perl-expresion is a Perl expression which must evaluate to true before the breakpoint is honored. If perl-expression is absent, any existing condition is removed; i.e., the breakpoint is made unconditional.
condition 5 x > 10 # Breakpoint 5 now has condition x > 10 condition 5 # Remove above condition
See also "break", "enable" and "disable".
delete [bp-number [bp-number...]]
Delete some breakpoints.
Arguments are breakpoint numbers with spaces in between. To delete all breakpoints, give no arguments.
See also the clear command which clears breakpoints by line number and info break to get a list of breakpoint numbers.
clear
info break
enable num [num ...]
Enables breakpoints, watch expressions or actions given as a space separated list of numbers which may be prefaces with an 'a', 'b', or 'w'. The prefaces are interpreted as follows:
If num is starts with a digit, num is taken to be a breakpoint number.
disable bp-number [bp-number ...]
Disables the breakpoints given as a space separated list of breakpoint numbers. See also info break to get a list of breakpoints
action position Perl-statement
Set an action to be done before the line is executed. If line is ., set an action on the line about to be executed. The sequence of steps taken by the debugger is:
.
For example, this will print out the value of $foo every time line 53 is passed:
$foo
watch Perl-expression
Stop very time Perl-expression changes from its prior value.
watch $a # enter debugger when the value of $a changes watch scalar(@ARGV)) # enter debugger if size of @ARGV changes.
The commands in this section show the call stack and let set a reference for the default call stack which other commands like list or break use as a position when one is not specified.
list
The most recent call stack entry is 0. Except for the relative motion commands up and down, you can refer to the oldest or top-level stack entry with -1 and negative numbers refer to the stack from the other end.
up
down
Beware that in contrast to debuggers in other programming languages, Perl really doesn't have an easy way for one to evaluate statements and expressions other than at the most recent call stack. There are ways to see lexical variables my and our, however localized variables which can hide global variables and other lexicals variables can be problematic.
"Print all or parts of the call stack (backtrace)"
"Select a call frame (frame)"
"Move to a more recent frame (up)"
"Move to a less recent frame (down)"
backtrace [count]
Print a stack trace, with the most recent frame at the top. With a positive number, print at most many entries.
In the listing produced, an arrow indicates the 'current frame'. The current frame determines the context used for many debugger commands such as source-line listing or the edit command.
edit
backtrace # Print a full stack trace backtrace 2 # Print only the top two entries
frame [frame-number]
Change the current frame to frame frame-number if specified, or the most-recent frame, 0, if no frame number specified.
A negative number indicates the position from the other or least-recently-entered end. So frame -1 moves to the oldest frame.
frame -1
frame # Set current frame at the current stopping point frame 0 # Same as above frame . # Same as above. 'current thread' is explicit. frame . 0 # Same as above. frame 1 # Move to frame 1. Same as: frame 0; up frame -1 # The least-recent frame
up [count]
Move the current frame up in the stack trace (to an older frame). 0 is the most recent frame. If no count is given, move up 1.
down [count]
Move the current frame down in the stack trace (to a newer frame). 0 is the most recent frame. If no count is given, move down 1.
"Define an alias (alias)"
"Remove an alias (unalias)"
"Define a macro (macro)"
"Allow remote connections (server)"
"Run debugger commands from a file (source)"
"Load or Reload something Perlish"
"Modify parts of the Debugger Environment"
alias alias command
Add alias alias for a debugger command command.
Add an alias when you want to use a command abbreviation for a command that would otherwise be ambigous. For example, by default we make s be an alias of step to force it to be used. Without the alias, s might be step, show, or set, among others.
s
show
set
alias cat list # "cat file.pl" is the same as "list file.pl" alias s step # "s" is now an alias for "step". # The above examples done by default.
For more complex definitions, see macro. See also unalias and show alias.
macro
unalias
show alias
unalias alias1 [alias2 ...]
Remove alias alias1 and so on.
Example:
unalias s # Remove 's' as an alias for 'step'
See also alias.
alias
macro macro-name sub { ... }
Define macro-name as a debugger macro. Debugger macros get a list of arguments which you supply without parenthesis or commas. See below for an example.
The macro (really a Perl anonymous subroutine) should return either a string or an array reference to a list of strings. The string in both cases are strings of debugger commands. If the return is a string, that gets tokenized by a simple split(/ /, $string). Note that macro processing is done right after splitting on ;; so if the macro returns a string containing ;; this will not be handled on the string returned.
split(/ /, $string)
;;
If instead, a reference to a list of strings is returned, then the first string is shifted from the array and executed. The remaining strings are pushed onto the command queue. In contrast to the first string, subsequent strings can contain other macros. Any ;; in those strings will be split into separate commands.
The below creates a macro called fin+ which issues two commands finish followed by step:
macro fin+ sub{ ['finish', 'step']}
If you wanted to parameterize the argument of the finish command you could do it this way:
macro fin+ sub{ \ ['finish', 'step ' . (shift)] \ }
Invoking with:
fin+ 3
would expand to ["finish", "step 3"]
["finish", "step 3"]
If you were to add another parameter, note that the invocation is like you use for other debugger commands, no commas or parenthesis. That is:
fin+ 3 2
rather than fin+(3,2) or fin+ 3, 2.
fin+(3,2)
fin+ 3, 2
See also info macro.
info macro
server [options]
options:
-p | --port NUMBER -a | --address
Suspends interactive debugger session and puts debugger in server mode which opens a socket for debugger connections
source [options] file
-q | --quiet | --no-quiet -c | --continue | --no-continue -Y | --yes | -N | --no -v | --verbose | --no-verbose
Read debugger commands from a file named file. Optional -v switch causes each command in FILE to be echoed as it is executed. Option -Y sets the default value in any confirmation command to be 'yes' and -N sets the default value to 'no'.
-v
-Y
-N
Option -q will turn off any debugger output that normally occurs in the running of the program.
-q
An error in any command terminates execution of the command file unless option -c or --continue is given.
-c
--continue
Sometimes in the middle of debugging you would like to make a change to a Perl module -- perhaps you've found a bug -- and start using that. If the change is inside a Perl module, you can use the command load module:
load module
load module {Perl-module-file}
Another thing that can occur especially if using Enbugger is that the source to Perl code is not cached inside the debugger and so you can't set a breakpoint on lines in that module. load source can be used to rectify this. However this is a bit experimenta. There may still be a problem in making sure that debugging turned on when tracing inside of that source.
load source
load source {Perl-source_file}
Finally, if you have debugger commands of your own or if you change a debugger command, you can force a reread of that debugger command using load command.
load command
load commmand {file-or-directory-name-1 [file-or-directory-name-2...]}
There are many parts of the debugger environment you can change, like the print line width, whether you want syntax highlighting or not and so on. These fall under set commands. show commands show you values that have been set. In fact, many of the set commands finish by runnin the corresponding "show" to echo you see what you've just set.
Set commands
Set to allow unique abbreviations of commands
Set controls for some "automatic" default behaviors
Set to show only file basename in showing file names
Set whether to confirm potentially dangerous operations.
Set debugging controls
Set to make sure 'next/step' move to a new position.
Set display attributes
Set whether we use terminal highlighting
Set maximum length sizes of various things
Set the value about to be returned
Influence how filenames in the debugger map to local filenames
Set to show elapsed time between debugger events
Set tracing of various sorts.
Set a my or our variable
Show commands
Show whether we allow abbreviated debugger command names
Show defined aliases
Arguments to restart program
Show controls for things with some sort of "automatic" default behavior
Show only file basename in showing file names
Show confirm potentially dangerous operations setting
Show debugging controls
Show status of 'set different'
Show display-related controls
Show whether we use terminal highlighting
Show whether debugger input is a terminal
Show "maximum length" settings
Show status of the timing hook
Set tracing of various sorts
Show debugger name and version
If the first non-blank character of a line starts with #, the command is ignored.
Commands are split at whereever ;; appears. This process disregards any quotes or other symbols that have meaning in Perl. The strings after the leading command string are put back on a command queue.
Within a single command, tokens are then white-space split. Again, this process disregards quotes or symbols that have meaning in Perl. Some commands like eval, macro, and break have access to the untokenized string entered and make use of that rather than the tokenized list.
eval
Resolving a command name involves possibly 4 steps. Some steps may be omitted depending on early success or some debugger settings:
1. The leading token is first looked up in the macro table. If it is in the table, the expansion is replaces the current command and possibly other commands pushed onto a command queue. See the "help macros" for help on how to define macros, and "info macro" for current macro definitions.
2. The leading token is next looked up in the debugger alias table and the name may be substituted there. See "help alias" for how to define aliases, and "show alias" for the current list of aliases.
3. After the above, The leading token is looked up a table of debugger commands. If an exact match is found, the command name and arguments are dispatched to that command. Otherwise, we may check to see the the token is a unique prefix of a valid command. For example, "dis" is not a unique prefix because there are both "display" and "disable" commands, but "disp" is a unique prefix. You can allow or disallow abbreviations for commands using "set abbrev". The default is abbreviations are on.
4. If after all of the above, we still don't find a command, the line may be evaluated as a Perl statement in the current context of the program at the point it is stoppped. However this is done only if "auto eval" is on. (It is on by default.)
If "auto eval" is not set on, or if running the Perl statement produces an error, we display an error message that the entered string is "undefined".
# This line does nothing. It is a comment and is useful # in debugger command files. # any amount of leading space is also ok
The following runs two commands: info program and list
info program
info program;; list
The following gives a syntax error since ;; splits the line and the simple debugger parse then thinks that the quote (") is not closed.
print "hi ;;-)\n"
If you have the Devel::Trepan::Shell plugin, you can go into a real shell and run the above.
If you want to continue a command on the next line use \ at the end of the line. For example:
\
eval $x = "This is \ a multi-line string"
The string in variable $x will have a \n before the article "a".
$x
\n
Some commands like step, or list do different things when an alias to the command ends in a particular suffix like ">".
Here are a list of commands and the special suffixes:
command suffix ------- ------ list > step +,-,<,> next +,-,<,> quit ! kill ! eval ?
See help on the commands listed above for the specific meaning of the suffix.
Because this should be useful in all sorts of environments such as back to perl 5.008, we often can make use of newer Perlisms nor can we require by default all of the modules, say for data printing, stack inspection, or interactive terminal handling. That said, if you have a newer Perl or the recommended modules or install plugins, you'll get more.
Although modular, this program is even larger than perl5db and so it loads a little slower. I think part of the slowness is the fact that there are over 70 or so (smallish) files (rather than one nearly 10K file) and because relative linking via rlib is used to glue them together.
perl5db
Rocky Bernstein
On writing a new Perl Debugger (Part 1 - Why?)
Devel::Trepan Debugger command aliases and command completion
Devel::Trepan Debugger evaluation of Perl statements
Location, Location, Location
Devel::Trepan github wiki
Devel::Trepan::Shell adds a debugger shell command support via Devel::REPL
shell
Devel::Trepan::Disassemble adds a debugger disassemble command support via B::Concise
disassemble
Devel::Callsite allows you to see the exact location of where you are stopped.
Enbugger allows you to enter the debugger via a direct call in source code
Eval::WithLexicals allows you to inspect my and our variables up the call stack
Data::Printer allows one to Use Data::Printer to format evaluation output
Data::Dumper::Perltidy allows one to Use Data::Dumper::Perltidy to format evaluation output
Term::ReadLine::Perl5 allows editing on the command line, command completion, and saving command history. This Module is preferred over Term::ReadLine::Perl or Term::ReadLine::Gnu.
Term::ReadLine::Gnu allows editing of the command line and command completion
perldebug is perl's built-in tried-and-true debugger that other debuggers will ultimately be compared with
Devel::ebug
DB is a somewhat abandoned debugger API interface. I've tried to use some parts of this along with perl5db.
Copyright (C) 2011, 2012 Rocky Bernstein <rocky@cpan.org>
This program is distributed WITHOUT ANY WARRANTY, including but not limited to the implied warranties of merchantability or fitness for a particular purpose.
The program is free software. You may distribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation (either version 2 or any later version) and the Perl Artistic License as published by O'Reilly Media, Inc. Please open the files named gpl-2.0.txt and Artistic for a copy of these licenses.
To install Devel::Trepan, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Devel::Trepan
CPAN shell
perl -MCPAN -e shell install Devel::Trepan
For more information on module installation, please visit the detailed CPAN module installation guide.