Another large bug in your code is that due to operator precedence, your dies won't work.

Basically, open FILE1,">$_[0]" || die "could not open $_[0]" is being interpreted as open FILE1,(">$_[0]" || die "could not open $_[0]")

$ perl -MO=Deparse -e 'open INP, "<", "hello" || die $!'              
+                               

open INP, '<', 'hello';
-e syntax OK



$ perl -MO=Deparse -e 'open(INP, "<", "hello") || die $!'             
+                                         
die $! unless open INP, '<', 'hello';
-e syntax OK



$ perl -MO=Deparse -e 'open INP, "<", "hello" or die "could not open: 
+$!"'                                                      
die $! unless open INP, '<', 'hello';
-e syntax OK
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You either need to use the lower-precedence or operator or call the open() function with parentheses.