How to recursively search for a repeated character in a text file and replace it with a new line using SED (e.g comma-delimited text)

Summary: 

In this post, I am going to show you how to search for repeated character in a text file and replace it with a new line to create a list. 

Problem or Goal: 

Take for example the task below, I have a log file containing parameters separated by a comma (","), see snippet below: 

3gdt,aace_support,access_restriction,adc,add,apn_conversion_wg,apn_redirection,apn_resolution_extension,attach_iot_limit,authentication_stationary_subscriber,conversational_qos_class,detach_inactive_subscriber_da,dual_access_support,dual_transfer_mode,ebm,edge_support,enhanced_uplink_mbr,gb_over_ip,gsm_adaptive_paging,gtp_user_location,gtpprime,gw_failure_restoration_gsm,gw_failure_restoration_wcdma,highest_qos_imsi,imei_check,integrated_traffic_capture,ipsec_support,lawful_interception,national_roaming_restriction,nw_init_sec_pdpctxt,payload_limit,pdp=1575,ps_ho,qos_hsdpa_mbr,rim_transfer,s_cdr_cause_code_ext,sau=2200,sau_lte=1,secondary_context,selective_service_request,sgsn_pool,sms_limit,srns_relocation,ss7_over_ip,streaming_qos_class,subscription_restriction,ue_signalling_control,ue_trace_mme

These are Ericsson SGSN-MME features, my task is to present these features in a neat list :-)

Cause:

Most log files are comma-delimited (Comma-delimited is a type of data format in which each piece of data is separated by a comma. This is a popular format for transferring data from one application to another, because most database systems are able to import and export comma-delimited data.)

Solution: 

The SED command below will read the file recursively and spit out a very nice list of Ericsson SGSN-MME features. 

linux-v7yi:/home# cat SGSN01-ER-SER-AD-Features-Summary.txt | sed -E 's/,/\n/g'

3gdt

aace_support

access_restriction

adc

add

apn_conversion_wg

apn_redirection

apn_resolution_extension

attach_iot_limit

authentication_stationary_subscriber

conversational_qos_class

detach_inactive_subscriber_da

dual_access_support

dual_transfer_mode

ebm

edge_support

enhanced_uplink_mbr

gb_over_ip

gsm_adaptive_paging

gtp_user_location

gtpprime

gw_failure_restoration_gsm

gw_failure_restoration_wcdma

highest_qos_imsi

imei_check

integrated_traffic_capture

ipsec_support

lawful_interception

national_roaming_restriction

nw_init_sec_pdpctxt

payload_limit

pdp=1575

ps_ho

qos_hsdpa_mbr

rim_transfer

s_cdr_cause_code_ext

sau=2200

sau_lte=1

secondary_context

selective_service_request

sgsn_pool

sms_limit

srns_relocation

ss7_over_ip

streaming_qos_class

subscription_restriction

ue_signalling_control

ue_trace_mme

Problem Solved?

Yes, a simpler example to understand is below:

linux-v7yi:/home# echo a,b,c,d,e,f,g,h,i,j,k | sed -E 's/,/\n/g'

a

b

c

d

e

f

g

h

i

j

k

linux-v7yi:/home#