There are likely as many ways of doing this as there are DocBook authors; however, here are two ways that you might find useful. Thanks to Y Giridhar Appaji Nag and Martin Brown for the markup used here.
Example D.1. Command Prompt with programlisting
<programlisting><prompt>#</prompt><userinput><command>cd</command>/some/dir</userinput><prompt>#</prompt><userinput><command>ls</command>-l</userinput></programlisting>
Displays as:
#cd /some/dir#ls -l
Example D.2. Command Prompt with screen
First create a general entity in the internal subset at the very
beginning of your document. This entity will define a name for the
shortcut which you can use to display the full prompt at any point
in your document.
<!ENTITY prompt "<prompt>[user@machine
~/dir]$</prompt>">
For more information about entities, read Section 8, “Entities (shortcuts, text macros and re-usable text)”.
<screen>&prompt;<userinput>cd /some/dir</userinput>&prompt;<userinput>ls -l</userinput></screen>
Displays as:
[user@machine ~/dir]$cd /some/dir[user@machine ~/dir]$ls -l
If you would like to add the output of your commands you can add
<computeroutput> text</computeroutput> within the
<screen> or <programlisting>
as appropriate.