You need to keep a buffer containing the lines you may need to throw away and print lines from the buffer when you know that they won't be thrown away. This stuff is tricky to get right because you have to correctly handle special cases for start up and ending conditions. Here's one way to do it:
use strict;
use warnings;
my $kPreLines = 1;
my $kPostLines = 1;
my $skipping;
my @bufferedLines;
while (defined (my $line = <DATA>) || @bufferedLines) {
push @bufferedLines, $line if defined $line;
while (@bufferedLines && $skipping) {
shift @bufferedLines;
--$skipping;
}
print shift @bufferedLines while @bufferedLines > $kPreLines + 1;
next if !@bufferedLines;
if ($bufferedLines[-1] =~ /XXXXX/) {
$skipping = $kPostLines;
@bufferedLines = ();
next;
}
next if defined $line;
print @bufferedLines;
last;
}
__DATA__
QQQQQ
PPPPP
XXXXX is my name
YYYYY
KKKKK
UUUUU
BBBBB
CCCCCC
XXXXX is what I play
KKKKK
NNNNN
Prints:
QQQQQ
KKKKK
UUUUU
BBBBB
NNNNN
Premature optimization is the root of all job security
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.
|