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3.5 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 -- User-defined 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. If a command has aliases, the aliases are given after the command name, separated by commas. If an alias has default arguments, the full definition of the alias is given after the first line. For example, here is the help display for the class status:

(gdb) help status
Status inquiries.

List of commands:

info, inf, i -- Generic command for showing things
        about the program being debugged
info address, iamain  -- Describe where symbol SYM is stored.
  alias iamain = info address main
info all-registers -- List of all registers and their contents,
        for selected stack frame.
...
show, info set -- 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. If that command has one or more aliases, GDB will display a first line with the command name and all its aliases separated by commas. This first line will be followed by the full definition of all aliases having default arguments.

apropos [-v] regexp

The apropos command searches through all of the GDB commands, and their documentation, for the regular expression specified in args. It prints out all matches found. The optional flag ‘-v’, which stands for ‘verbose’, indicates to output the full documentation of the matching commands and highlight the parts of the documentation matching regexp. For example:

apropos alias

results in:

alias -- Define a new command that is an alias of an existing command
aliases -- User-defined aliases of other commands

while

apropos -v cut.*thread apply

results in the below output, where ‘cut for 'thread apply’ is highlighted if styling is enabled.

taas -- Apply a command to all threads (ignoring errors
and empty output).
Usage: taas COMMAND
shortcut for 'thread apply all -s COMMAND'

tfaas -- Apply a command to all frames of all threads
(ignoring errors and empty output).
Usage: tfaas COMMAND
shortcut for 'thread apply all -s frame apply all -s COMMAND'
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 Command, Variable, and Function Index point to all the sub-commands. See Command and Variable Index.

info

This command (abbreviated i) is for describing the state of your program. For example, you can show the arguments passed to a function 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 several 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
info copying

Display information about permission for copying GDB.

show warranty
info warranty

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

show configuration

Display detailed information about the way GDB was configured when it was built. This displays the optional arguments passed to the configure script and also configuration parameters detected automatically by configure. When reporting a GDB bug (see GDB Bugs), it is important to include this information in your report.


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