Last week I've described how you can extend the exec-mode CLI commands with almost no knowledge of Tcl. A bit more work is required if your commands include Tcl special characters (quotes, braces or backslashes).

For example, to display all routes advertised by customers of AS X, you'd use the following show command: show ip bgp regexp _X_([0-9]+)(_\1)*$ (the regular expression is explained in the AS-path based filter of customer BGP routes post). This command cannot be entered as a Tcl string with variable substitution; Tcl would interpret the [ and \ characters. You could enter the whole command in curly braces, but then there would be no variable substitution that we need to insert command line parameters. To make Tcl happy, use the following Tcl commands:

1. set cmd {first-part-of-command} stores the command prefix into the cmd variable;
2. append cmd $argv appends the command line arguments to the command;
3. append cmd {rest-of-command} appends the rest of the IOS exec command;
4. puts [exec $cmd] executes the command and prints the results.

For example, the following code will display the customers of a BGP AS specified in the command line (after being stored in a flash file and defined in an alias, of course):

set cmd {show ip bgp regexp _}
append cmd $argv
append cmd {_([0-9]+)(_\1)*$}
puts [exec $cmd]