Ack searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN.
but that doesn't seem to be the current behavior anymore, is it? Currently it seems that it does not read from standard input if no files are named.
The information in the man page in file https://github.com/petdance/ack2/blob/dev/ack#L1136 seems to be wrong as it states that
Ack searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN.
but that doesn't seem to be the current behavior anymore, is it? Currently it seems that it does not read from standard input if no files are named.