Beefy Boxes and Bandwidth Generously Provided by pair Networks
Don't ask to ask, just ask

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Don't use Perl if you don't want to read the whole file in
Sure you can do this in perl without reading the whole file. Here's some code (untested) (updated to fix a couple of mistakes).
#!/usr/bin/perl -w use strict; my $file = shift or die; open my $fh, "+<$file" or die "$!"; my $size = 4096; my ($cur_pos, $buf); seek $fh, -$size, 2; while (1) { $cur_pos = tell $fh; read $fh, $buf, $size; last if $buf =~ m/\S/s; seek $fh, -$size, 1; } $buf =~ m/(\s+)$/s; $cur_pos += $-[0]; truncate $fh, $cur_pos; close $fh; exit 0;
This will read only what is necessary and does not keep what it has already processed.

I am sure there are better ways of doing this.


Update: I finally got some time and tested the above and found another bug (fixed in the code above). I was not supposed to use sysread and seek<code> together (<code>sysseek will probably do fine), so I changed the sysread to <code>read<code>, and it worked ok.

(Note to self: Never post untested code.)

In reply to Re: Re: Remove Blank Lines Off the End of a File by PrakashK
in thread Remove Blank Lines Off the End of a File by jbisbee

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others drinking their drinks and smoking their pipes about the Monastery: (11)
    As of 2018-09-26 10:46 GMT
    Find Nodes?
      Voting Booth?
      Eventually, "covfefe" will come to mean:

      Results (205 votes). Check out past polls.

      • (Sep 10, 2018 at 22:53 UTC) Welcome new users!