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gdb(1)				   GNU Tools				gdb(1)



NAME
       gdb - The GNU Debugger

SYNOPSIS
       gdb    [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev]
	      [-s symfile] [-e prog] [-se prog] [-c core] [-x cmds] [-d dir]
	      [prog[core|procID]]

DESCRIPTION
       The  purpose  of	 a debugger such as GDB is to allow you to see what is
       going on ''inside'' another program while it executes--or  what	another
       program was doing at the moment it crashed.

       GDB  can	 do four main kinds of things (plus other things in support of
       these) to help you catch bugs in the act:


	  ?   Start your program, specifying anything that  might  affect  its
	      behavior.


	  ?   Make your program stop on specified conditions.


	  ?   Examine what has happened, when your program has stopped.


	  ?   Change  things  in your program, so you can experiment with cor-
	      recting the effects of one bug and go on to learn about another.


       You  can	 use  GDB  to  debug programs written in C, C++, and Modula-2.
       Fortran support will be added when a GNU Fortran compiler is ready.

       GDB is invoked with the shell command gdb.  Once started, it reads com-
       mands  from the terminal until you tell it to exit with the GDB command
       quit.  You can get online help from gdb itself  by  using  the  command
       help.

       You can run gdb with no arguments or options; but the most usual way to
       start GDB is with one argument or two, specifying an executable program
       as the argument:

       gdb program


       You  can	 also  start  with  both an executable program and a core file
       specified:

       gdb program core


       You can, instead, specify a process ID as a  second  argument,  if  you
       want to debug a running process:

       gdb program 1234


       would  attach  GDB  to  process 1234 (unless you also have a file named
       '1234'; GDB does check for a core file first).

       Here are some of the most frequently needed GDB commands:

       break [file:]function
	       Set a breakpoint at function (in file).

       run [arglist]
	      Start your program (with arglist, if specified).

       bt     Backtrace: display the program stack.

       print expr
	       Display the value of an expression.

       c      Continue running your program (after stopping, e.g. at a	break-
	      point).

       next   Execute  next program line (after stopping); step over any func-
	      tion calls in the line.

       edit [file:]function
	      look at the program line where it is presently stopped.

       list [file:]function
	      type the text of the program in the  vicinity  of	 where	it  is
	      presently stopped.

       step   Execute  next program line (after stopping); step into any func-
	      tion calls in the line.

       help [name]
	      Show information about GDB command name, or general  information
	      about using GDB.

       quit   Exit from GDB.

       For full details on GDB, see Using GDB: A Guide to the GNU Source-Level
       Debugger, by Richard M. Stallman and Roland H. Pesch.  The same text is
       available online as the gdb entry in the info program.

OPTIONS
       Any  arguments  other  than options specify an executable file and core
       file (or process ID); that is, the first argument encountered  with  no
       associated option flag is equivalent to a '-se' option, and the second,
       if any, is equivalent to a '-c' option if it's  the  name  of  a	 file.
       Many  options have both long and short forms; both are shown here.  The
       long forms are also recognized if you truncate them, so long as	enough
       of  the	option	is present to be unambiguous.  (If you prefer, you can
       flag option arguments with '+' rather than '-',	though	we  illustrate
       the more usual convention.)

       All  the	 options  and command line arguments you give are processed in
       sequential order.  The order makes a difference when the '-x' option is
       used.


       -help

       -h     List all options, with brief explanations.


       -symbols=file

       -s file
	       Read symbol table from file file.


       -write Enable writing into executable and core files.


       -exec=file

       -e file
		Use file file as the executable file to execute when appropri-
	      ate, and for examining pure data	in  conjunction	 with  a  core
	      dump.


       -se=file
		Read  symbol table from file file and use it as the executable
	      file.


       -core=file

       -c file
	       Use file file as a core dump to examine.


       -command=file

       -x file
	       Execute GDB commands from file file.


       -directory=directory

       -d directory
	       Add directory to the path to search for source files.



       -nx

       -n     Do not  execute  commands	 from  any  '.gdbinit'	initialization
	      files.  Normally, the commands in these files are executed after
	      all the command options and arguments have been processed.



       -quiet

       -q     ''Quiet''.  Do not print the  introductory  and  copyright  mes-
	      sages.  These messages are also suppressed in batch mode.


       -batch Run  in batch mode.  Exit with status 0 after processing all the
	      command files specified with '-x' (and '.gdbinit', if not inhib-
	      ited).  Exit with nonzero status if an error occurs in executing
	      the GDB commands in the command files.

	      Batch mode may be useful for running GDB as a filter, for	 exam-
	      ple  to download and run a program on another computer; in order
	      to make this more useful, the message

	      Program exited normally.


	      (which is ordinarily issued whenever a program running under GDB
	      control terminates) is not issued when running in batch mode.


       -cd=directory
		Run  GDB  using directory as its working directory, instead of
	      the current directory.


       -fullname

       -f     Emacs sets this option when it runs GDB  as  a  subprocess.   It
	      tells  GDB  to  output  the  full file name and line number in a
	      standard, recognizable fashion each time a stack frame  is  dis-
	      played  (which includes each time the program stops).  This rec-
	      ognizable format looks like two ' 32'  characters,  followed  by
	      the  file	 name, line number and character position separated by
	      colons, and a newline.  The Emacs-to-GDB interface program  uses
	      the  two ' 32' characters as a signal to display the source code
	      for the frame.


       -b bps  Set the line speed (baud rate or bits per second) of any serial
	      interface used by GDB for remote debugging.


       -tty=device
		Run using device for your program's standard input and output.



SEE ALSO
       'gdb' entry in info; Using GDB: A Guide to the GNU Source-Level	Debug-
       ger, Richard M. Stallman and Roland H. Pesch, July 1991.

COPYING
       Copyright (c) 1991 Free Software Foundation, Inc.

       Permission  is  granted	to make and distribute verbatim copies of this
       manual provided the copyright notice and	 this  permission  notice  are
       preserved on all copies.

       Permission  is granted to copy and distribute modified versions of this
       manual under the conditions for verbatim	 copying,  provided  that  the
       entire  resulting derived work is distributed under the terms of a per-
       mission notice identical to this one.

       Permission is granted to copy and distribute translations of this  man-
       ual into another language, under the above conditions for modified ver-
       sions, except that this permission notice may be included  in  transla-
       tions approved by the Free Software Foundation instead of in the origi-
       nal English.



GNU Tools			   22may2002				gdb(1)
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