#! /usr/bin/gawk -f

BEGIN { 
  if (key == "") 
    { printf "must specify -v 'key=xxx'\n"; exit 1 }
  for (i=-5; i <= 5; i++) wd[i] = ""
}

function push(x,  i)
{ 
  for (i=-5; i <= 4; i++) wd[i] = wd[i+1]; 
  wd[5] = x;
  if (wd[0] == key)
    { len = 50;
      for (i=-5; i < 0; i++) len -= length(wd[i]);
      for (i= 0; i < len; i++) printf " ";
      for (i=-5; i <= 5; i++) printf "%s ", wd[i];
      printf "\n";
    }
}

/./ { push($0); }

END { for(i=1; i<=5; i++) push(""); }