Equivalent to retrieving the contents and looking for a line that starts with ${fieldName}: (the fieldName argument followed by a colon). The remainder of the line (everything after the first colon) will be trimmed and returned.

For example, if you run pass google.com/personal and get the following output:

hunter2 username: johnsmith full_email:johnsmith@gmail.com app_password: abcd 1234 efgh 5678

Then fieldFor("google.com/personal", "app_password") would return abcd 1234 efgh 5678.