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Re: Mimick tac with python.

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From Terry Reedy <tjreedy@udel.edu>
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Subject Re: Mimick tac with python.
Date Sat, 30 Jan 2016 04:38:54 -0500
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On 1/30/2016 1:03 AM, Christian Gollwitzer wrote:
> 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?

One could read the file by lines and make a list of start-of-line 
positions.  Reverse the list. Read each line.  Details omitted.

-- 
Terry Jan Reedy

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Thread

Mimick tac with python. Hongyi Zhao <hongyi.zhao@gmail.com> - 2016-01-30 04:46 +0000
  Re: Mimick tac with python. Random832 <random832@fastmail.com> - 2016-01-29 23:58 -0500
    Re: Mimick tac with python. Christian Gollwitzer <auriocus@gmx.de> - 2016-01-30 07:03 +0100
      Re: Mimick tac with python. Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-01-30 09:56 +0200
        Re: Mimick tac with python. Christian Gollwitzer <auriocus@gmx.de> - 2016-01-30 10:23 +0100
      Re: Mimick tac with python. Peter Otten <__peter__@web.de> - 2016-01-30 09:21 +0100
      Re: Mimick tac with python. Terry Reedy <tjreedy@udel.edu> - 2016-01-30 04:38 -0500
    Re: Mimick tac with python. Hongyi Zhao <hongyi.zhao@gmail.com> - 2016-01-30 06:18 +0000
  Re: Mimick tac with python. Chris Angelico <rosuav@gmail.com> - 2016-01-30 15:56 +1100

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