Here's a slight variation. This one prints the line before and after the
line(s) that match (the amount of lines is controlled by the variable
$range). It uses a circular buffer, but all the functionality
of dealing with circularity is hidden inside a
tie mechanism.
#!/opt/perl/bin/perl
use strict;
use warnings;
my $file = "/usr/dict/words";
my $word = "perl";
my $range = 1; # -$range .. $range
my $size = 2 * $range + 1;
sub TIEARRAY {bless [("") x $_ [1]] => $_ [0]}
sub STORE {${$_ [0]} [$_ [1] % @{$_ [0]}] = $_ [2]}
sub FETCH {${$_ [0]} [$_ [1] % @{$_ [0]}]}
sub FETCHSIZE {scalar @{$_[0]}}
sub STORESIZE {die}
tie my @buffer => 'main', $size;
open my $fh => $file or die "Failed to open $file: $!";
while (<$fh>) {
$buffer [$.] = $_;
if ($buffer [$. - $range] =~ /$word/) {
print @buffer [$. - $size + 1 .. $.];
}
}
# Borderline, matches at the end:
for my $line ($. - $range + 1 .. $.) {
print @buffer [$line - $range .. $.] if $buffer [$line] =~ /$word/
+;
}
__END__
-- Abigail