Replace existing date with new format

Question

I have a 4GB JSON file in which there are multiple Date fields. the Date format is 2021-10-15T06:02:50.455Z. I want to replace this format with a simple date and time like this 2021-10-15T06:02:50

Is there any way I can do this with sed command
sed -e 's/[1-9][0-9]\{3\}-[0-9]\{2\}-[0-1][0-9]T[0-3][0-9]:[0-9]\{2\}:[0-9]\{2\}.[0-9]\{3\}Z/magic_here/g' test.json

I'm looking forward to Linus script but node or python also worked.

PS: regex is working fine

Answer 1

This look like task where zero-length assertion might be useful, consider following example in python:

import re
txt = "something 2021-10-15T06:02:50.455Z something"
clean = re.sub(r'(?<=\d\d\d\d-\d\d-\d\dT\d\d:\d\d:\d\d)\.\d+Z','',txt)
print(clean)

output

something 2021-10-15T06:02:50 something

Explanation: Just remove \.\d+Z which are after pattern describing datetime part you want to preserve. Note that I used so called raw-string to make escaping easier, see re module docs for further discussion. Note that . needs to be espaced as it is denoting literal dot. \d denotes any digit. This solution might be reworked to any regex tool supporting positive lookbehind assertion.