Is there a word for "truncate to size zero", preferably one which could be used and understood in the following way:
"...ing the file" := "truncating the file to zero bytes"?
RECAP: The best answers so far seem to be "empty the file", "zero the file size" and "truncate to (size|length) zero". In a suitable context, "truncate" has "truncate to (size|length) zero" as the default meaning (esp. since it's the commonest specific length to which files are truncated) but it's by no means the only one
O_TRUNC
without breaking lots of code.man fopen
uses "Truncate file to zero length" once explicitly and from then on just "truncate" for the same concept, the zero length thus being understood