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The debugger understands the following commands:
- h
- Prints out a summary help message
- h [command]
- Prints out a help message for the given debugger command.
- h h
-
The special argument of h h produces the entire help page, which is quite
long.
If the output of the h h 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
You may change the pager which is used via o pager=... command.
- p expr
-
Same as print {$DB::OUT} expr in the current package. In particular, because
this is just Perl's own print function, this means that nested data structures
and objects are not dumped, unlike with the x command.
The DB::OUT filehandle is opened to /dev/tty, regardless of where
STDOUT may be redirected to.
- x [maxdepth] expr
-
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 print
function in Perl. When dumping hashes, you'll probably prefer 'x \%h' rather than 'x %h'.
See Dumpvalue if you'd
like to do this yourself.
The output format is governed by multiple options described under "Configurable Options".
If the maxdepth is included, it must be a numeral N; the value is
dumped only N levels deep, as if the dumpDepth option had been
temporarily set to N.
- V [pkg [vars]]
-
Display all (or some) variables in package (defaulting to main) 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 $)
there, just the symbol names, like this:
Use ~pattern and !pattern for positive and negative regexes.
This is similar to calling the x command on each applicable var.
- X [vars]
- Same as
V currentpackage [vars].
- y [level [vars]]
- Display all (or some) lexical variables (mnemonic:
mY variables) in the
current scope or level scopes higher. You can limit the variables that you see with vars
which works exactly as it does for the V and X commands. Requires
the PadWalker module version 0.08 or higher; will warn if this isn't installed.
Output is pretty-printed in the same style as for V and the format is
controlled by the same options.
- T
- Produce a stack backtrace. See below for details on its output.
- s [expr]
- 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.
- n [expr]
- 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.
- r
- Continue until the return from the current subroutine. Dump the return value if the
PrintRet
option is set (default).
- <CR>
- Repeat last
n or s command.
- c [line|sub]
- Continue, optionally inserting a one-time-only breakpoint at the specified line or
subroutine.
- l
- List next window of lines.
- l min+incr
- List
incr+1 lines starting at min.
- l min-max
- List lines
min through max. l - is synonymous to -.
- l line
- List a single line.
- l subname
- List first window of lines from subroutine. subname may be a variable that contains
a code reference.
- -
- List previous window of lines.
- v [line]
- View a few lines of code around the current line.
- .
- Return the internal debugger pointer to the line last executed, and print out that line.
- f filename
-
Switch to viewing a different file or eval statement. If filename is
not a full pathname found in the values of %INC, it is considered a regex.
evaled strings (when accessible) are considered to be filenames: f (eval
7) and f eval 7\b access the body of the 7th evaled string
(in the order of execution). The bodies of the currently executed eval and of evaled
strings that define subroutines are saved and thus accessible.
- /pattern/
- Search forwards for pattern (a Perl regex); final / is optional. The search is
case-insensitive by default.
- ?pattern?
- Search backwards for pattern; final ? is optional. The search is case-insensitive by
default.
- L [abw]
- List (default all) actions, breakpoints and watch expressions
- S [[!]regex]
- List subroutine names [not] matching the regex.
- t
- Toggle trace mode (see also the
AutoTrace option).
- t expr
- Trace through execution of
expr. See perldebguts/"Frame
Listing Output Examples" for examples.
- b
- Sets breakpoint on current line
- b [line] [condition]
-
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 if:
b 237 $x > 30
b 237 ++$count237 < 11
b 33 /pattern/i
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- b subname [condition]
- Set a breakpoint before the first line of the named subroutine. subname may be a
variable containing a code reference (in this case condition is not supported).
- b postpone subname [condition]
- Set a breakpoint at first line of subroutine after it is compiled.
- b load filename
- Set a breakpoint before the first executed line of the filename, which should be a
full pathname found amongst the %INC values.
- b compile subname
- Sets a breakpoint before the first statement executed after the specified subroutine is
compiled.
- B line
- Delete a breakpoint from the specified line.
- B *
- Delete all installed breakpoints.
- a [line] command
-
Set an action to be done before the line is executed. If line 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
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
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For example, this will print out $foo every time line 53 is passed:
a 53 print "DB FOUND $foo\n"
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- A line
- Delete an action from the specified line.
- A *
- Delete all installed actions.
- w expr
- Add a global watch-expression. We hope you know what one of these is, because they're
supposed to be obvious.
- W expr
- Delete watch-expression
- W *
- Delete all watch-expressions.
- o
- Display all options
- o booloption ...
- Set each listed Boolean option to the value
1.
- o anyoption? ...
- Print out the value of one or more options.
- o option=value ...
-
Set the value of one or more options. If the value has internal whitespace, it should be
quoted. For example, you could set o pager="less -MQeicsNfr" to call less
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: o option='this isn\'t bad' or o option="She said, \"Isn't
it?\"".
For historical reasons, the =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 =. The option can be abbreviated, but for
clarity probably should not be. Several options can be set together. See "Configurable Options" for a list of these.
- < ?
- List out all pre-prompt Perl command actions.
- < [ command ]
- Set an action (Perl command) to happen before every debugger prompt. A multi-line command
may be entered by backslashing the newlines. WARNING If
command is
missing, all actions are wiped out!
- << command
- Add an action (Perl command) to happen before every debugger prompt. A multi-line command
may be entered by backwhacking the newlines.
- > ?
- List out post-prompt Perl command actions.
- > command
- Set an action (Perl command) to happen after the prompt when you've just given a command
to return to executing the script. A multi-line command may be entered by backslashing the
newlines (we bet you couldn't've guessed this by now). WARNING If
command
is missing, all actions are wiped out!
- >> command
- Adds an action (Perl command) to happen after the prompt when you've just given a command
to return to executing the script. A multi-line command may be entered by backslashing the
newlines.
- { ?
- List out pre-prompt debugger commands.
- { [ command ]
-
Set an action (debugger command) to happen before every debugger prompt. A multi-line
command may be entered in the customary fashion. WARNING If command is
missing, all actions are wiped out!
Because this command is in some senses new, a warning is issued if you appear to have
accidentally entered a block instead. If that's what you mean to do, write it as with ;{
... } or even do { ... }.
- {{ command
- Add an action (debugger command) to happen before every debugger prompt. A multi-line
command may be entered, if you can guess how: see above.
- ! number
- Redo a previous command (defaults to the previous command).
- ! -number
- Redo number'th previous command.
- ! pattern
- Redo last command that started with pattern. See
o recallCommand, too.
- !! cmd
- Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See
o shellBang,
also. Note that the user's current shell (well, their $ENV{SHELL} variable)
will be used, which can interfere with proper interpretation of exit status or signal and
coredump information.
- source file
- Read and execute debugger commands from file. file may itself contain
source
commands.
- H -number
- Display last n commands. Only commands longer than one character are listed. If number
is omitted, list them all.
- q or ^D
-
Quit. ("quit" doesn't work for this, unless you've made an alias) This is the
only supported way to exit the debugger, though typing exit twice might work.
Set the inhibit_exit option to 0 if you want to be able to step off the end
the script. You may also need to set $finished to 0 if you want to step through global
destruction.
- R
-
Restart the debugger by exec()ing a new session. We try to maintain your
history across this, but internal settings and command-line options may be lost.
The following setting are currently preserved: history, breakpoints, actions, debugger
options, and the Perl command-line options -w, -I, and -e.
- |dbcmd
- Run the debugger command, piping DB::OUT into your current pager.
- ||dbcmd
- Same as
|dbcmd but DB::OUT is temporarily selected as well.
- = [alias value]
-
Define a command alias, like
or list current aliases.
- command
- Execute command as a Perl statement. A trailing semicolon will be supplied. If the Perl
statement would otherwise be confused for a Perl debugger, use a leading semicolon, too.
- m expr
- List which methods may be called on the result of the evaluated expression. The expression
may evaluated to a reference to a blessed object, or to a package name.
- M
- Displays all loaded modules and their versions
- man [manpage]
-
Despite its name, this calls your system's default documentation viewer on the given
page, or on the viewer itself if manpage is omitted. If that viewer is man,
the current Config information is used to invoke man using the proper
MANPATH or -M manpath option. Failed lookups of the form XXX that
match known manpages of the form perlXXX will be retried. This lets you type man
debug or man op from the debugger.
On systems traditionally bereft of a usable man command, the debugger invokes perldoc.
Occasionally this determination is incorrect due to recalcitrant vendors or rather more
felicitously, to enterprising users. If you fall into either category, just manually set the
$DB::doccmd variable to whatever viewer to view the Perl documentation on your system. This
may be set in an rc file, or through direct assignment. We're still waiting for a working
example of something along the lines of:
$DB::doccmd = 'netscape -remote http://something.here/';
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