You could try something like this: 

use strict;
use warnings;

open (my $in,"<", "/tmp/logbook.log") or die "can not open datei: $!";
my @errors = grep /error/i, <$in>;
my $file = '/tmp/ok.txt';
open my $out, ">", $file or die "Kann Datei $file nicht zum Schreiben 
+oeffnen: $!\n";
if (@errors) {
   print $out @errors;
}
else {
   print $out "OK!\n";
}
close($in);
close($out);

[download]


If the logbook.log file has something like this:
line1 has an error
line2 does not
ERROR on line 3
the following output is in the ok.txt file:

line1 has an error
ERROR on line 3

In reply to Re: Write a file if grep finds a pattern? by mjscott2702
in thread Write a file if grep finds a pattern? by matze77

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.