First off, you can pick up the entire file in one bang by setting $/

open(IN,"somefile.pl");
undef $/;
$string = <IN>;
[download]

save yourself a while and a join.

$string = q{ 
print "Content-type:text/html\n\n";
print "Some big hunk of code\n";
print("Content-type:text/html","\n","\n");
print ('Content-type: text/html',"\n","\n");
print "Yet another big hunk of code\n";
print "Yet more big hunks of code\n";
print ("Content-type: text/html"); print 'Content-type: text/html',"\n
+\n";
print "Some other big hunk of code that does something really cool\n";
print ("Content-type: text/html"); print 'CONTENT-type: text/html' , "
+\n", "\n";
print "Some code that ends the program\n";
};

print $string,"\n";

$string =~ s/print[\s'"\(]+content-type:\s*text\/html[\\nr\s'"\),]+;//
+gi;

print "---------------\n";
print $string,"\n";
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This covered all the 'normal' ways of printing a line that I could think of. I you run across any more, I'll update the expression.
/\/\averick