Regex specific match - regex

Question

Want to filter exact FOC2345N1UG from the following input. I had used this regex (S\/N:\s\s\s(\S+)) in Python. I am fetching all the ones not the one which is required.
NODE module 0/RSP0/CPU0 ASR 9001, Route Switch Processor with 8GB memory
MAIN: board type 0x100401
S/N: FOC21456NKN7
Top Assy. Number: 00-0000-00
PID: ASR9001-RP
HwRev (UDI_VID): V01
Chip HwRev: V1.0
New Deviation Number: 0
CLEI:
Board State : IOS XR RUN
PLD: Motherboard: N/A, Processor version: 0x8023 (rev: 3.0), Power: N/A
MONLIB: QNXFFS Monlib Version 3.3
ROMMON: Version 3.4(20160331:102636) [ASR9K ROMMON]
Board FPGA/CPLD/ASIC Hardware Revision:
IntCtrl : V0.0
USB0 : V17.0
ClkCtrl : V0.0
CPUCtrl : V0.0
MLANSwitch : V0.0
EOBCSwitch : V2.0
LIU : V0.0
YDTI : V0.0
PHY : V0.0
CBC (active partition) : v22.114
CBC (inactive partition) : v22.114
NODE fantray 0/FT0/SP ASR-9001 Fan Tray Ver 2
MAIN: board type 0x900409
S/N: FOC21456NTQF
Top Assy. Number: 68-5333-03
PID: ASR-9001-FAN-V2
HwRev (UDI_VID): V03
Chip HwRev: V1.0
New Deviation Number: 0
CLEI: IPUCBLBBAA
Vendor ID: 5
PLD: Motherboard: N/A, Processor version: N/A, Power: N/A
Board FPGA/CPLD/ASIC Hardware Revision:
CBC (active partition) : v24.115
CBC (inactive partition) : v24.115
NODE module 0/0/CPU0 ASR 9001, Modular Line Card
MAIN: board type 0xf10402
S/N: FOC2124NL345L
Top Assy. Number: 00-0000-00
PCA: 73-14312-08
PID: ASR9001-LC
HwRev (UDI_VID): V01
Chip HwRev: V1.0
New Deviation Number: 0
CLEI:
Board State : IOS XR RUN
PLD: Motherboard: N/A, Processor version: 0x8023 (rev: 3.0), Power: N/A
ROMMON: Version 3.4(20160331:133429) [ASR9K ROMMON]
Board FPGA/CPLD/ASIC Hardware Revision:
NP0 : V4.194
NP1 : V4.194
FIA0 : V0.2
FIA1 : V0.2
X-Bar : V1.5
CPUCtrl : V1.18
FabArbiter : V0.0
PortCtrl : V1.18
PHYCtrl : V1.18
ClkCtrl : V1.18
PHY0 : V0.4(HwRev) V8.0(FwRev) V8.0(SwRev)
DBCtrl : V2.10
Power Sequencer0 : V0.0
Power Sequencer1 : V0.0
Power Sequencer2 : V0.0
Modular Linecard Daughter board : V1.0
CBC (active partition) : v23.114
CBC (inactive partition) : v23.114
SPA 0/0/0 : ASR 9000 4-port 10GE Modular Port Adapter
MAIN: board type 0237
68-5885-01 rev B0
dev N/A
S/N FOC2346NHB7
PCA: 73-17858-01 rev N/A
PID: A9K-MPA-4X10GE
VID: V06
CLEI: IPUIBRDRAF
Board State : OK
FPD Software Revision:
SPA 0/0/1 : ASR 9000 4-port 10GE Modular Port Adapter
MAIN: board type 0237
68-5885-01 rev B0
dev N/A
S/N FOC22345NH71
PCA: 73-17858-01 rev N/A
PID: A9K-MPA-4X10GE
VID: V06
CLEI: IPUIBRDRAF
Board State : OK
FPD Software Revision:
NODE power-module 0/PS0/M0/SP ASR-9001 AC Power Supply
MAIN: board type 0xf00404
S/N: ART22784X093
Top Assy. Number: 341-0424-01
PID: A9K-750W-AC
HwRev (UDI_VID): V01
Chip HwRev: V0.0
New Deviation Number: 0
CLEI: IPUPAJAAAA
Board State : PRESENT
PLD: Motherboard: N/A, Processor version: N/A, Power: N/A
Board FPGA/CPLD/ASIC Hardware Revision:
NODE power-module 0/PS0/M1/SP ASR-9001 AC Power Supply
MAIN: board type 0xf00404
S/N: ART21274X095
Top Assy. Number: 341-0424-01
PID: A9K-750W-AC
HwRev (UDI_VID): V01
Chip HwRev: V0.0
New Deviation Number: 0
CLEI: IPUPAJAAAA
Board State : PRESENT
PLD: Motherboard: N/A, Processor version: N/A, Power: N/A
Board FPGA/CPLD/ASIC Hardware Revision:
Rack 0 - ASR-9001 Chassis
RACK NUM: 0
S/N: FOC2345N1UG
PID: ASR-9001
VID: V07
Desc: ASR-9001 Chassis
CLEI: IPMDX00BR

Answer 1

Use the re.S flag to dotall along with the reg
/ASR-9001 Chassis.+S\/N:\s+([A-Z\d]+)/
This finds your target header, skips everything up until the next S/N:, then grabs the next sequence of upper alpha and digit characters.
>>> import re
>>> re.search(r"ASR-9001 Chassis.+S\/N:\s+([A-Z\d]+)", data, re.S).group(1)
'FOC2345N1UG'
I notice some of your serial numbers have missing :s in them and the data is generally loosely formatted, so you may need to make that optional with S\/N:? and make other tweaks depending on your use case.

Answer 2

I think you need the S/N followed by PID, so the regexp should be like this:
m = re.match(r"S/N: (\w+) PID", content)
sn = m.group(0)
Here is the example