This is a formula snippet for Google Sheets to prepare the From column in WP Engine regex URL redirects.

wpengine-regex-url-rewrites-from-column.txt

/*==========================

1.) Google Sheets spreadsheet should have a sheet named 'source' and a another called 'target'.
2.) 'source' sheet should contain raw/unprocessed export of 'From' and 'To' columns. Therefore, column selectors may need updating.
3.) Copy and paste each of the formulas below as appropriate into your 'target' sheet.

==========================*/

/*. From column */
=ARRAYFORMULA(
  IF(LEN(source!A2:A),
     IF(REGEXMATCH(source!A2:A, "\.[a-zA-Z0-9]+$"),
        "^" & REGEXEXTRACT(source!A2:A, "https?://[^/]+(/.*)"),
        "^" & REGEXREPLACE(REGEXEXTRACT(source!A2:A, "https?://[^/]+(/.*)"), "/$", "") & "/?$"
     ),
  )
)

/*. To column */
=ARRAYFORMULA(IF(LEN(source!B2:B), source!B2:B, ))