What is the error in this code

[Vincent Cannavale]

#open a text file for reading, since opening for writing wipes the file
open(INFILE, "<perlfile.txt");
#assign the file, identified by the file handle to an array, then "transform"
#the array into a scalar variable by joining each element in the array
#(a line) with a new line character
$variable = join(@variable = <INPUT>, "\n");
close(INFILE);
open(OUTFILE, ">perlfile.txt");

$variable =~ s/0/zero/g ;
$variable =~ s/1/one/g ;
$variable =~ s/2/two/g ;
$variable =~ s/3/three/g ;
$variable =~ s/4/four/g ;
$variable =~ s/5/five/g ;
$variable =~ s/6/six/g ;
$variable =~ s/7/seven/g ;
$variable =~ s/8/eight/g ;
$variable =~ s/9/nine/g ;

#print the changed text back to the file and close it.
print OUTFILE "$variable";
close(OUTFILE);