Following code will help you.

use strict;
use warnings;

print "Enter the string:";
my $string=<STDIN>; #getting the input from user
 
chomp($string); #remove the newline at end in string

if($string=~/^[a-z]+$/) { #checking whether the string is in lowercase
print "String given in Lower Case:$string\n";
$string=~s/([a-z])/\u$1/g; #replacing the string to be in upper case
print "Uppercase String:$string\n";
}
elsif($string=~/^[A-Z]+$/) { #checking whether the string is in upperc
+ase
print "String given  in Upper Case:$string\n";
$string=~s/([A-Z])/\l$1/g; #replacing the string to be in lower case
print "Lowercase String:$string\n";
}
elsif($string=~/^[a-zA-Z]+$/) { #checking whether the string is in mix
+ed case
print "String given in Mixed Case:$string\n";
$string=~s/([a-z])/\u$1/g; #replacing the string to be in upper case
print "Uppercase String:$string\n";
$string=~s/([A-Z])/\l$1/g; #replacing the string to be in lower case
print "Lowercase String:$string\n";
}
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