Sort files by date and copy every other to new folder

Question

I was wondering what would be the most concise way of sorting files by date and then copying every other to a new folder.

My problem: I've got files renamed such that they are called

file1 (101)
file2 (103)
file3 (110)
.
.
.

where the numbering is not indicative of the intrinsic file difference. The only thing that's really different between the two file types I want to sort is their alternating creation date, therefore my rather convoluted above problem statement.

To sort the files by date you can use `ls -t` _"-t sort by modification time, newest first"_. What do you mean with "copying every other"? PS> Do not parse the output of `ls` you can incur in [problems](http://unix.stackexchange.com/a/128987/66388). — Hastur, Jan 20 '16 at 14:40
Thanks for that already! After sorting I want to copy every other file to a new folder, meaning that I take the first file, copy it, skip the second file, take the third one, copy it, skip the fourth and so on. — lhcgeneva, Jan 20 '16 at 14:44
Have you considered that if someone (human or program) touches (or added) a file you will get a mess... :-) Even that if you generate(d) or copied those files really fast, they can be modified (=closed) in an asynchronous way? ... [Think weird because it sadly happens each day]. — Hastur, Jan 20 '16 at 14:50
:D good point! Initially the files were named properly so I could distinguish the two 'classes' of files by name. Then I batch renamed on windows, as I assumed it would work similar to MacOs' finder. Not a good idea because it made 1600 files of the exact same name, only adding a number at the very end. Only thing I know is that the two file classes were created alternatingly. — lhcgeneva, Jan 20 '16 at 14:56
__Start again from the original files, if you can.__ You can do some tests maybe, but you cannot seriously work if you are not sure `100%` about the data. Which kind of results will you obtain? Note that when you proceed _lossy_, relying on the sureness that a major failure will warn you if something is not correct... the [Murphy's_law](https://en.wikipedia.org/wiki/Murphy's_law) will show. If those files are of a different kind (check with `file file1 file2`) you can rely a little more. You can wipe out the doubts with `md5sum` on local and original copy... — Hastur, Jan 20 '16 at 15:05
They are imaging files, so I can easily distinguish and check them afterwards. Which makes me wonder why I haven't been loading them all in one go in a bog standard image analysis software to then split that stack the way I like it. Thanks anyway :) — lhcgeneva, Jan 20 '16 at 15:08

score 1 · Accepted Answer · edited Apr 13 '17 at 12:37

The following script seems to be a good one but it will work only if you have "well behaving" filenames ^[1]:

#!/bin/bash
foo=0
for f in $(ls -rt) ; do 
  if [ $((foo%2)) -eq 0 ];
    then
       echo "even " "$f";  // maybe here copy
    else
       echo "odd" "$f" ;   // maybe here skip
  fi
  let foo++
done

So essentially no newlines, no tab, no spaces... as it seems in your case.
Please remember that is not safe to parse the output of ls ^[1] and doublecheck always.

If you are not in the safe area in which you can use ls, then you may consider to find a solution with find, maybe taking some inspiration from Gilles' answer ^[2].

Ps> In case of data corruption, even in a light case as yours, it always needed to check that the patch worked. Often is more convenient to start again from the beginning. If, as I guess, the data size is huge and you cannot transfer/download it again, it's always possible to do some check (e.g. md5sum^[3]) on the original data and the patched one.

I knew but __remember,remember,remember__ all the warning. :) — Hastur, Jan 20 '16 at 16:47

Sort files by date and copy every other to new folder

1 Answers1