Beefy Boxes and Bandwidth Generously Provided by pair Networks
Just another Perl shrine
 
PerlMonks  

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

If you want to slurp the entire file, don't read it line by line and then build up a giant $printout string. That will result (internally) in lots of copying and reallocating of larger memory chunks as the string grows. ...Perl's pretty smart, but you could almost look at that technique as an optimized version of Schlemiel the Painter's Algorithm. As you append, Perl has to allocate a larger chuncks of memory, and move the entire string to the new, larger locations.

Better to just slurp it in one step using one of the following:

my $string = do{ open my $fh, '<', 'filename' or die $!; local $/ = undef; <$fh>; };

...or...

use File::Slurp; my $text = read_file('filename');

...or...

use File::Slurp; my @lines = read_file('filename');

Any of the above ought to be relatively efficient, though the File::Slurp methods are easier on the eyes. But if reading the file line by line (your existing approach) is too slow, slurping is only going to yield incremental savings, at best. Either way, you've got to touch the entire file. Line-by-line approaches tend to work out well, and scale well.

You're probably already aware of this, but if the file size is large enough to swamp physical memory, slurping is not a good approach.


Dave


In reply to Re: printout of large files. loop vs. flush at once by davido
in thread printout of large files. loop vs. flush at once by ISAI student

Title:
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?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others romping around the Monastery: (4)
    As of 2018-07-21 12:01 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?
      It has been suggested to rename Perl 6 in order to boost its marketing potential. Which name would you prefer?















      Results (448 votes). Check out past polls.

      Notices?