Am 30.01.16 um 08:56 schrieb Jussi Piitulainen:
Christian Gollwitzer writes:
Am 30.01.16 um 05:58 schrieb Random832:
On Fri, Jan 29, 2016, at 23:46, Hongyi Zhao wrote:
awk '{a[NR]=$0} END {while (NR) print a[NR--]}' input_file
perl -e 'print reverse<>' input_file
Well, both of those read the whole file into memory - tac is sometimes
smarter than that, but that makes for a more complex program.
Now I'm curious. How is it possible to output the first line as last
again if not by remembering it from the every beginning? How could tac
be implemented other than sucking up everything into memory?
It may be possible to map the data into virtual memory so that the
program sees it as an array of bytes. The data is paged in when
accessed. The program just scans the array backwards, looking for
end-of-line characters. I believe they can be identified reliably, as
bytes, even in a backward scan of UTF-8-encoded data.
The data needs to be in a file.
If it's in a file, then I agree. I was thinking about the case where tac
is used in a pipe - obviously here you can't reverse the file in
constant memory.
Christian
--
https://mail.python.org/mailman/listinfo/python-list
