Before using dbx to debug a program, compile the program using the –g option (for example, cc –g). The –g option includes additional debugging information in your program object so that dbx can list local variables and find source lines.

If you use dbx to debug code that was not compiled using the –g option, local variables are invisible to dbx, and source lines may appear to jump around oddly as a result of various optimizations. It is more difficult to debug code without reliable references to lines of source code.

This section summarizes a few things you need to know if you compile and link your program with Dynamic Shared Objects (DSOs). A DSO is a relocatable shared library. By linking with a DSO, you keep your program size small and use memory efficiently.

If you compile and link with DSOs, dbx automatically notices their use in the program and picks up the relevant debugging information. The dbx command listobj shows any DSOs in a process. The dbx command whichobj lists all DSOs in which a specified variable is present. The dbx command listregions identifies DSO addresses at run time.

The dbx help section on hint_dso has more information on dbx and DSOs. For more information on DSOs, see "Using Dynamic Shared Objects" in the Compiling and Performance Tuning Guide.

This section describes how to invoke dbx and includes:

To invoke dbx from the shell command line, type dbx. The syntax is:

dbx [options] [object_file [corefile]]

(dbx) 

You can start your program under dbx using the run or rerun command.

The run command does not invoke the initialization files of the Bourne, C, and Korn shells before it starts a program. If you use a non-standard shell, before you run a program set the dbx variable $shellparameters to a string that will instruct the shell to not load the initialization file. For example, for the C shell you would enter set $shellparameters = "-f".To verify exactly how your application is being started by the run or rerun command, start dbx with the -d option.

If the environment variable SHELL is set to a C shell and your program has file-descriptors other than the default values: 0,1,2, switch to the Bourne shell before you invoke the run command. This means you can only use sh-style redirections, but csh would close the extra file-descriptors. Make the switch, for the purpose of running your program, with the dbx command setenv SHELL /bin/sh.

A run command must appear on a line by itself and cannot be followed by another dbx command separated by a semi-colon (;). Terminate the command line with a return (new-line). Note that you cannot include a run command in the command list of a when command.

The sort command takes an input file and produces a sorted output file; you can specify input and output files either through command-line arguments or file redirection.

For example, from the command line you can enter:

% sort -i input -o output
% sort < input2 > output2

If you are debugging the sort program, the equivalent dbx commands are:

(dbx) run -i input -o output
(dbx) run < input2 > output2

If you execute these run commands in the order presented, you can repeat the last run command by using the rerun command:

(dbx) rerun

You can use an editor to create a .dbxinit command file. This file contains various dbx commands that automatically execute when you invoke dbx. You can put any dbx command in the .dbxinit file. If a command requires input, the system prompts you for it when you invoke dbx.

On invocation, dbx looks for a .dbxinit file in the current directory. If the current directory does not contain a .dbxinit file, dbx looks for one in your home directory. (This assumes that you have set the IRIX system HOME environment variable.)

The dbx command help has several options:

When you type help all, dbx displays the file using the command name given by the dbx$pager variable. The dbx help file is large and can be difficult to read even if you use a simple paging program like more(1). You can set the $pager variable to a text editor like vi(1) or to your favorite editor.

For example, just add the following command in your .dbxinit file:

set $pager = "vi"

When the above entry is in your .dbxinit file, dbx displays the help file in vi. You can then use the editor's search commands to look through the help file quickly. Quit the editor to return to dbx.

You can use a semicolon (;) as a separator to include multiple commands on the same command line. This is useful with commands such as when (described in "Writing Conditional Commands") as it allows you to include multiple commands in the command block. For example:

(dbx) when at "myfile.c":37 {print a ; where ; print b}

You can use a backslash (\) at the end of a line of input to indicate that the command is continued on the next line. This can be convenient when entering complex commands such as an alias definition (aliases are discussed in "Creating and Removing dbx Aliases").

For example:

(dbx) alias foll "print *(struct list *)$p ; \
set $p = (int)((struct list *)($p))->next"

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Tip: You can also use the hed command for creating and modifying commands. "The History Editor" has details on this command.

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To invoke a subshell, enter sh at the dbx prompt, or enter sh and a shell command at the dbx prompt. After invoking a subshell, type exit or <Ctrl-d> to return to dbx.

The syntax for the sh command is:

For example, to spawn a subshell, enter:

(dbx) sh
% 

To display the end of the file datafile, enter:

(dbx) sh tail datafile

To end a dbx debugging session, enter the quit command at the dbx prompt:

(dbx) quit