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in reply to Re^2: How can you sysread an entire file?
in thread How can you sysread an entire file?

I would recommend it because it's the least memory-intensive approach, and you're potentially using a lot of memory already. (Best would of course be to read the file line-by-line, but since you can't do that, this is the next best thing I could come up with.)

As to the other, you didn't stipulate what you wanted to do with the records when you had them split, and I needed a dummy subroutine to show the outline right (and to note that your data is found in $1). Blame the chatterbox for the odd word choice. :-)


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Re^4: How can you sysread an entire file?
by NeilF (Sexton) on Jan 14, 2006 at 17:22 UTC
    OK :)

    Here's an example...

        my $rec;
    sysopen(DF,"test.txt", O_RDONLY | O_CREAT);
    sysread(DF, $rec, -s DF);
    close DF;

    # Split up records into array.
    # Will lose \n on recs - add later.
    @test=split("\n",$rec);

    # Do some work on @test
     Work... Work... Work...

    # Build up into a single record, putting \n back in
    my $rec;foreach(@test){$rec.=$_."\n";}

    sysopen(DF,"test.txt", O_WRONLY | O_CREAT);
    syswrite DF,$rec;
    close DF;

    [download]
    Does that help set the scene a little better? :)

    So basically I want to make this as efficient as possible. I have to use SYSREAD and SYSWRITE to make the IO as optimal as possible. ie: Reading a 1 meg file would take 2000 IO processes if buffered!!!!! SYSREAD will in effect take 1!
[reply]
[d/l]

      It won't affect your IO count but 

      my $rec;foreach(@test){$rec.=$_."\n";}

      [download]

      Is much better coded as 

      my $rec = join "\n", @test;

      [download]

      roughly 3 times faster on 1000 elements.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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[reply]
[d/l]
[select]
        Thanks! Anything like that is most appreciated!
[reply]

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