#! perl -slw
use strict;

my @lines;
my %seen;
while( <DATA> ) {
    push @lines, $_;
    my $buf = join '', @lines;
    if( $buf =~ /(.{30}these\s+are\s+my\s+keywords.{30})/sm ) {
        print "'$1'" unless $seen{ $1 };
        ++$seen{ $1 };
    }
    shift @lines if @lines > 5;
}

__END__
Here is my text file
I want to save a bunch of
charcaters before the keywords
for example the keywords might be
the phrase: these are my keywords
I want to save a bunch of characters
after the keywords too so I have
context

The keywords may appear multiple
times in any given file and may
span across lines like so: these are
my keywords.  This is one reason
I was using slurp instead of reading
in line by line

##</code><code>##

C:\test>junk
'eywords might be
 the phrase: these are my keywords
 I want to save a bunch of ch'
'y
 span across lines like so: these are
 my keywords.  This is one reason
 I was u'