Replacing a substring within a string in Perl can be achieved using the s/old_string/new_string/ operator. This operator stands for "substitute", and it is used to replace the first occurrence of a specified substring with a new string.
Here's a simple example to demonstrate how to replace a substring within a string in Perl:
$mystring = "The quick brown fox jumps over the lazy dog";
$mystring =~ s/brown/red/;
print $mystring;
In the code above, we first declare a variable named $mystring and assign it with a string that reads "The quick brown fox jumps over the lazy dog". We then use the s/old_string/new_string/ operator to replace the substring brown with red. Finally, we print out the new string value.
The output of the code above would be:
The quick red fox jumps over the lazy dog
It's also possible to replace all occurrences of a specified substring by using the g (global) modifier. Here's an example:
$mystring = "The quick brown fox jumps over the lazy dog";
$mystring =~ s/o/O/g;
print $mystring;
In this example, we use the s/old_string/new_string/g operator to replace all occurrences of the letter o with an uppercase O. The output of the code would be:
The quick brOwn fOx jumps Over the lazy dOg
The s/old_string/new_string/ operator can also be combined with regular expressions, allowing for more complex and flexible string manipulation.