Regex - Match word/letters underneath a specific pattern

Very unusual one but I'm trying to match output from an SSH session that may collapse view and fall underneath the output required (like a collapsed column)...

Take a look at the example output:

      System Id     Interface          Circuit Id        State HoldTime Type     PRI
--------------------------------------------------------------------------------
rtr1.lab01.some GE0/0/1            0000000001         Up   22s      L2       -- 
thing                                                                              
rtr2.lab01.some GE0/0/2            0000000002         Up   24s      L2       -- 
thingelse

I can match the the first line with:

^([a-zA-Z0-9][a-zA-Z0-9.-]+[a-zA-Z0-9])

which returns (rtr1.lab01.some and rtr2.lab01.some) but I'm trying to find the easiest way to match it based on the full hostname (rtr1.lab01.something and rtr2.lab01.somethingelse)

I'm also matching the rest of the output perfectly fine and able to extract the data but really can't find a way to achieve what I'm trying... Can someone point me in the right direction? To expand further (for more context... I'm using the Google TextFSM in Python to match all this data from an SSH session)

Solution

import re

text = """System Id     Interface          Circuit Id        State HoldTime Type     PRI
--------------------------------------------------------------------------------
rtr1.lab01.some GE0/0/1            0000000001         Up   22s      L2       --
thing
rtr2.lab01.some GE0/0/2            0000000002         Up   24s      L2       --
thingelse
rtr2.lab01.abcd GE0/0/4            0000000003         Up   24s      L2       --
rtr2.lab01.none GE0/0/24           0000000004         Up   24s      L2       --
sense
rtr2.lab01.efgh GE0/0/5            0000000003         Up   24s      L2       --
"""

lines = text.rstrip().split('\n')[2:]
n_lines = len(lines)
current_line = -1

def get_next_line():
    # Actual implementation would be reading from a file and yielding lines one line at a time
    global n_lines, current_line, lines
    current_line += 1
    # return special sentinel if "end of file"
    return  lines[current_line] if current_line < n_lines else '$'


def get_system_id():
    line = None
    while line != '$': # loop until end of file
        if line is None: # no current line
            line = get_next_line()
            if line == '$': # end of file
                return
        m = re.search(r'^([a-zA-Z0-9][a-zA-Z0-9.-]+[a-zA-Z0-9])', line)
        id = m[1]
        line = get_next_line() # might be sentinel
        if line != '$' and re.match(r'^[a-zA-Z0-9]+$', line): # next line just single id?
            id += line
            line = None # will need new line
        yield id

for id in get_system_id():
    print(id)

Prints:

rtr1.lab01.something
rtr2.lab01.somethingelse
rtr2.lab01.abcd
rtr2.lab01.nonesense
rtr2.lab01.efgh

See Python Demo