Dear monks,

I have some files which I would like to parse somehow using regular expressions. The files could be several gigabytes or even up to a terabyte in size, so loading the files to memory is not an option.

The files are not guaranteed to have line breaks, and it is not known in advance if the search pattern exists in a certain file, where it is and how often it occurs.

Hence the question: Is it possible to let a regular expression act directly on a file *without* reading any part of the file to memory?

Sorry if this has been answered already; of course, I have tried to do my homework, but probably used the wrong search keywords (I just found the usual posts or tutorials where people suggest to read the whole file into a scalar variable and let the regular expression act on that variable, or to split the file in chunks and test each chunk etc.).

Thank you very much for any thoughts,

Nocturnus

In reply to Possible to have regexes act on file directly (not in memory) by Nocturnus

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, details, 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, summary, 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.