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 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 alias
     

results in:

          
          alias -- Define a new command that is an alias of an existing command
          aliases -- Aliases of other commands
          d -- Delete some breakpoints or auto-display expressions
          del -- Delete some breakpoints or auto-display expressions
          delete -- Delete some breakpoints or auto-display expressions
          
     

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 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 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

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.