s/To_be_replaced/Replacement/

s/To_be_replaced/Regular_Expression/e;

#!/usr/bin/perl
  
# Defining the string to be converted
String = "Geeks for Geeks is the best";
print "Original String:String\n";
  
# Converting the string to UPPERCASE
# using 'uc' Function
String =~ s/(\w+)/uc(1)/ge;
print"Uppercased String: String\n";
  
# Converting the string to lowercase
# using 'lc' FunctionString =~ s/(\w+)/lc(1)/ge;
print"Lowercased String:String\n";

Original String: Geeks for Geeks is the best
Uppercased String: GEEKS FOR GEEKS IS THE BEST
Lowercased String: geeks for geeks is the best

#!/usr/bin/perl
  
# Defining the string to be converted
String = "Geeks for Geeks is the best";
print "Original String:String\n";
  
# Converting a single character using e modifier
String =~ s/(e)/uc(1)/ge;
print"Updated String: String\n";
  
# Converting a word using e modifierString =~ s/(for)/uc(1)/ge;
print"Updated String:String\n";

Original String: Geeks for Geeks is the best
Updated String: GEEks for GEEks is thE bEst
Updated String: GEEks FOR GEEks is thE bEst

#!/usr/bin/perl
  
# Subroutine for substitution operation
sub subroutine
{
    regex = shift;
    regex =~ s/Friday/Tuesday/;
    return regex;
}
  
# Defining the string to be convertedString = "Monday Friday Wednesday";
print "Original String: String\n";
  
# Calling the subroutine for substitutionString =~ s/(\w+)/subroutine(1)/ge;
print"Updated String:String\n";
  
  
# Defining a new String to be converted
String2 = "Today is Friday";
print "\nOriginal String:String2\n";
  
# Calling the subroutine for substitution
String2 =~ s/(\w+)/subroutine(1)/ge;
print"Updated String: $String2\n";

Original String: Monday Friday Wednesday
Updated String: Monday Tuesday Wednesday

Original String: Today is Friday
Updated String: Today is Tuesday