#! /usr/bin/perl -w

my $target = shift || 'word';
my $re = qr/a=<(.*?$target.*?)>/;

while( <DATA> ) {
    print "[$1]\n" if /$re/;
}

__DATA__
a=<wordy>
b=<rappinghood>
a=<thisword>
b=<thatword>
a=<foreword>
b=<junk>
a=<nothing>
b=<word>
b=<wordplay>
a=<swords>
b=<end>