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Debugging with GDB

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3.3 Getting help

You can always ask GDB itself for information on its commands, using the command help.

help
h
You can use help (abbreviated h) with no arguments to display a short list of named classes of commands:

 
(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without
stopping the program user-defined -- User-defined commands Type "help" followed by a class name for a list of commands in that class. Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb)

help class
Using one of the general help classes as an argument, you can get a list of the individual commands in that class. For example, here is the help display for the class status:

 
(gdb) help status
Status inquiries.

List of commands:

info -- Generic command for showing things
 about the program being debugged
show -- Generic command for showing things
 about the debugger

Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

help command
With a command name as help argument, GDB displays a short paragraph on how to use that command.

apropos args
The apropos args command searches through all of the GDB commands, and their documentation, for the regular expression specified in args. It prints out all matches found. For example:

 
apropos reload

results in:

 
set symbol-reloading -- Set dynamic symbol table reloading
                                 multiple times in one run
show symbol-reloading -- Show dynamic symbol table reloading
                                 multiple times in one run

complete args
The complete args command lists all the possible completions for the beginning of a command. Use args to specify the beginning of the command you want completed. For example:

 
complete i

results in:

 
if
ignore
info
inspect

This is intended for use by GNU Emacs.

In addition to help, you can use the GDB commands info and show to inquire about the state of your program, or the state of GDB itself. Each command supports many topics of inquiry; this manual introduces each of them in the appropriate context. The listings under info and under show in the Index point to all the sub-commands. See section Index.

info
This command (abbreviated i) is for describing the state of your program. For example, you can list the arguments given to your program with info args, list the registers currently in use with info registers, or list the breakpoints you have set with info breakpoints. You can get a complete list of the info sub-commands with help info.

set
You can assign the result of an expression to an environment variable with set. For example, you can set the GDB prompt to a $-sign with set prompt $.

show
In contrast to info, show is for describing the state of GDB itself. You can change most of the things you can show, by using the related command set; for example, you can control what number system is used for displays with set radix, or simply inquire which is currently in use with show radix.

To display all the settable parameters and their current values, you can use show with no arguments; you may also use info set. Both commands produce the same display.

Here are three miscellaneous show subcommands, all of which are exceptional in lacking corresponding set commands:

show version
Show what version of GDB is running. You should include this information in GDB bug-reports. If multiple versions of GDB are in use at your site, you may need to determine which version of GDB you are running; as GDB evolves, new commands are introduced, and old ones may wither away. Also, many system vendors ship variant versions of GDB, and there are variant versions of GDB in GNU/Linux distributions as well. The version number is the same as the one announced when you start GDB.

show copying
Display information about permission for copying GDB.

show warranty
Display the GNU "NO WARRANTY" statement, or a warranty, if your version of GDB comes with one.


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