my @words = qw(data set); 
 
open FILE1, "file.txt"; 
my @file = <FILE1> 
close FILE1; 
 
open FILE2, ">>file2.txt"; 
foreach (@file){ 
 foreach my $word (@words){ 
     if($word eq $_){ 
         print FILE2 uc($_); 
     }else { 
         print FILE2 $_; 
    } 
 } 
} 
close FILE2

 #!/usr/bin/perl    
use strict;    
use warnings;    
  
my $code = <<EOF;    
data output;    
set input;    
if varname=1 then var_flag=1;    
else var_flag=0;    
run;    
EOF    
  
my $keywords = <<EOF;    
data    
set    
if    
then    
else    
run    
EOF    
  
my $keyword;    
{    
	local $/; # slurp the keyword file (in this limited scope)    
	open my $kw, "<", \$keywords;    
	$keyword = join "|", split ' ', <$kw>;    
	close $kw;    
}    
  
open my $c, "<", \$code;    
while (<$c>) {    
	s/($keyword)/uc $1/eg;    
	print;    
}   
close $c; 
__END__ 
 
{ 
	local $^I = '.bak'; 
	local @ARGV = ("code.txt", ..., ...  ); 
	while (<>) { 
		s/($keyword)/uc $1/eg;    
		print;  			 
	} 
}