import re
 
output = "sgncs1#sh ver Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6, RELEASE SOFTWARE (fc1) Copyright (c) 1986-2009 by Cisco Systems, Inc. Image text-base: 0x00003000, data-base: 0x012A99FC ROM: Bootstrap program is C3550 boot loader sgncs1 uptime is 5 weeks, 2 days, 20 hours, 12 minutes System image file is \"flash:c3550-ipservicesk9-mz.122-44.SE6.bin\" Cisco WS-C3550-24 (PowerPC) processor (revision G0) with 65526K/8192K Processor board ID CHK0644W0KC Model number: WS-C3550-24-SMI System serial number: CHK0644W0KC"
regex_serial2 = re.compile(r'System serial number:\s(\S+)')
serial2 = regex_serial2.findall(output)
print(serial2)

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