Re: Using File::ReadBackwards or equivalent on pre-existing file handle

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Re^2: Using File::ReadBackwards or equivalent on pre-existing file handle by HYanWong (Acolyte) on Jun 25, 2014 at 23:25 UTC
p.s. am I better unshifting the lines then doing a `print(FH) foreach (@arr);` or pushing the lines then doing a `print(FH) foreach (reverse @arr);`? I suppose I'm asking, is pushing faster than unshifting (I assume yes), and does perl make a new array copy when it does a `foreach (reverse ...)`, or is it clever enough just to iterate backwards over the array. I presume it's clever...	[reply] [d/l] [select]
Re^3: Using File::ReadBackwards or equivalent on pre-existing file handle by Anonymous Monk on Jun 26, 2014 at 00:57 UTC
To sure, profile & benchmark the variations. `print ... for reverse @list` will generate a new, complete list I think (currently cannot find the right B magic to produce the optree display supporting the claim).	[reply] [d/l]
Re^3: Using File::ReadBackwards or equivalent on pre-existing file handle by Laurent_R (Canon) on Jun 26, 2014 at 06:19 UTC
Difficult to say without testing. I think that slurping the file from the FH directly into an array will be slightly faster than `push`ing or `unshift`ing it line by line. Then `pop`ing the lines to be printed might be faster than using `reverse`, but only a benchmark can really say. You might even get diffrent results with differents versions of Perl. Overall, the difference is likely to be small or almost unsignificant.	[reply] [d/l] [select]
Re^2: Using File::ReadBackwards or equivalent on pre-existing file handle by HYanWong (Acolyte) on Jun 25, 2014 at 23:02 UTC
It's only a 70Mb text file, so saving in memory is probably OK actually. Cheers	[reply]