Regular expression differences between sed 4.2.2 and 4.5

[SAMUEL VISCAPI]

Dear all,

I believe we just stumbled upon one of the key differences between sed 4.2.2 on 
CentOS 7 and sed 4.5 on RedHat 8.

We found out some time ago that one of our application errors out when fed some 
XML file containing incorrect date formats, e.g different from 
“YYYY-MM-DDTHH:MM:SS”

For some unknown reason, the seconds get truncated from the date, leading to 
some error further down the line.

The workaround we are trying to put in place with sed is:

1/  find those occurrences of bad date format in the XML file, e.g: 
<EventDateTime>2021-08-17T06:06</EventDateTime>

2/ prepend each occurrence with “:00” (the missing seconds), e.g: 
<EventDateTime>2021-08-17T06:06:00</EventDateTime>

The regular expression we use reads as follows:

sed -i 
'/[0-9/][0-9/][0-9/][0-9/]-[0-9/][0-9/]-[0-9/][0-9/]T[0-9/][0-9/]:[0-9/][ 
0-9/]</ 
s/[0-9/][0-9/][0-9/][0-9/]-[0-9/][0-9/]-[0-9/][0-9/]T[0-9/][0-9/]:[0-9/][0-9/]/&:00/g'
 somefile.xml

It’s running just fine on our development environment (sed 4.2.2 on CentOS 7), 
but fails on RedHat 8 where a more recent version of sed is installed (4.5). It 
looks like as if the regular expression no longer works the same, and matches 
large chunks of the XML file instead of just the erroneous date.

What would be in your opinion the right command to use with sed 4.5 on RedHat 8 
?

Thank you all in advance for your help.

Best regards

Samuel
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