open my $in,  '<', 'infile'  or die $!; # open input file
open my $out, '>', 'outfile' or die $!; # open output file
while(my $line = <$in>){
  chomp $line;                       # remove newline
  if( $line =~ s/key1=([^&\s]+)// ){ # capture value in $1 while 
                                     #   replacing with empty string
    $line .= " key1=$1";             # append key and value to line
  }
  print $out "$line\n";              # print line to output file
}
close $in;
close $out;