Here's a version without Tie::File and with minimal buffering:
use strict;
use warnings;
use Getopt::Std;

our %opts;
getopts('A:B:n',\%opts);
die "USAGE: $0 [-n] [-An] [-Bn] pattern [file] ..." unless @ARGV;
my $pattern = shift;


my @buffer;
my @matches;

my $nextmatch;
my $prevmatch;
my $linenum;
my $shownames;
my $fname;
my $showlines = $opts{n};
my $behind = $opts{B} || 0;
my $after  = $opts{A} || 0;
my $bufsize = 1 + $behind;

if (@ARGV == 0) {
  procfile("-");
} else {
  $shownames = 1 if @ARGV > 1;
  procfile($fname) while ($fname = shift @ARGV);
}

sub procfile {
  $prevmatch = -2 - $after;
  $linenum = 0;
  $nextmatch = 0;
  my $f = shift;
  unless (open IN, "<$f") {
    warn "$0: $f: $!\n";
    return;
  }
  while (<IN>) {
    push @buffer, $_;
    my  $matched = m/$pattern/o;
    push @matches, $matched;
    $linenum++;
    $nextmatch = $linenum if $matched;
    if (@buffer >= $bufsize) {
      proconeline();
    }
  }
}

proconeline() while @buffer && ($nextmatch || $prevmatch);

sub proconeline {
  my $oldlinenum = $linenum - @buffer + 1;
  my $oldmatch   = shift @matches;
  $_ = shift @buffer;
  if ($oldmatch || $oldlinenum - $prevmatch <= $after || $nextmatch) {
    print "$fname:" if $shownames;
    print "$oldlinenum:" if $showlines;
    print;
  }
  $prevmatch = $oldlinenum if $oldmatch;
  $nextmatch = 0 if $oldlinenum == $nextmatch;
}

[download]

In reply to Re: linux grep feature by Thelonius
in thread Emulating GNU grep -A and -B switches with perl (was: linux grep feature) by perlisfun

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.