How to extract a field based on character count?

[eamuncal]

I have a field name X with the following value: 0123456789.
I want to create another field that is based on the first 4 characters of the field name X.
Then call it Y.

Any idea on how to do this? If its in bash my way would be to use cut -c1-4

Trying the regex and rex to no avail.

Thanks in advance.

emn.

[Ayn · Accepted solution]

This should do it:

rex field=X "^(?<Y>\d{4})"

[eamuncal]

This sure did it! Thanks Ayn