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### 3.6 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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