Insert character Cisco IOS EEM Script

Question

I am extracting the ip address of an interface and using that address' 3rd octet as part of the BGP AS number. I need to insert a 0 before the number if the 3rd octet is < 10. For example, if 3rd octet = 8 then BGP AS = 11108

Here is my current and unfinished applet.

event manager applet replace
event none
action 1.0 cli command "conf t"
action 1.1 cli command "do show ip int brief vlan 1"
action 1.2 regexp " [0-9.]+ " $_cli_result ip match
action 2.0 regexp {([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+)} $_cli_result match ip
action 2.1 regexp {([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)} $ip match first second third forth
action 2.2 set vl1 $first.$second.$third.$forth
action 2.3 cli command "router bpg 111$third"

Answer 1

The simplest method here is to use format with the right formatting sequence. (If you've ever used sprintf() in C, you'll understand what the format command does straight off. Except the Tcl command doesn't have any problems with buffer overruns or other tricky bits like that.)

# Rest of your script unchanged; I'm lazy so I'll not repeat it here
set bpg [format "652%02d" $third]
action 2.3 cli command "router bpg $bpg"

The key here is that %02d does formatting (%) of a decimal number (d) in a zero-padded (0) field of width two (2). And there's a literal 652 in front of it (no % there so literal).

You can roll the above into a single line if you want, but I think it is much clearer to write it in two (there's really no good excuse for writing unclear code, as it just makes your life harder later and it doesn't really take much less time to write clearly in the first place):

action 2.3 cli command "router bpg [format 652%02d $third]"