# In fat crayon mode for your pleasure
# spoofing your big log file handle as a little array for brevity
my @logs = ();
for(1..20){push(@logs, $_)}


my $lookBack    = 2;   # the number of lines behind the match you want
my $lookAhead   = 2;   # the number of lines ahead the match you want
my $matchReg    = '9'; # what your matching on (can be inlined)
my $matched     = 0;   # flag when we have a match
my @buffer      = ();  # your lookBack buffer

# Iterate through the logs looking for match
foreach my $line (@logs) {

   # Feed the buffer
   push(@buffer, $line);
   # Trim the buffer
   shift(@buffer) if $#buffer > ($lookBack-1);
   # Do stuff if this line matches
   if ($line =~ /$matchReg/) {

      # Print the buffer
      for(@buffer){print "lookback: $_\n"}
      # Wave a flag we have a match
      $matched = $lookAhead;
      # Nothing else to see here, move along
      next;
        
    }

    # Still working the lookAhead from a prior match?
    if($matched){

       # one less match
       --$matched;
       print "LookAhead: $line\n";

    }
}

[download]

In reply to Re: grab 'n' lines from a file above and below a /match/ by Anonymous Monk
in thread grab 'n' lines from a file above and below a /match/ by barathbr

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.