How to count the number of matches in a Perl string?

In Perl, we can find the number of matches in a string by different approaches. In this tutorial, we will discuss the three most widely used approaches.

Searching for a Single Character in a Perl String

Let's first take the case where we would want to search for a single character pattern in a string. For example, let's suppose we have a string that look something like this −

"India.Japan.Russia.USA.China" 

And, we want to find the number of times "." (dot) appears in the above string.

Example

Consider the code shown below.

my $countries = "India.Japan.Russia.USA.China";
print "The given string is: ", $countries;
print "\n";
my @countDotOccurrences = $countries =~ /\./g;
print "Number of dots in the string: ", scalar @countDotOccurrences;

Output

If you run the above code in a Perl compiler online, then you will get the following output in the terminal −

The given string is: India.Japan.Russia.USA.China
Number of dots in the string: 4

Example

Now let's take another approach that will also allow us to find the occurrence of a single character in a Perl string. Consider the code shown below.

$someString = "Perl Codes Can Be Difficult To Read";
print "The given string is: ", $someString;
print "\n";
$countT = ($someString =~ tr/T//);
$countX = ($someString =~ tr/X//);
print "$countT T characters in the string\n";
print "$countX X characters in the string";

Output

If you run the above code in a Perl compiler, then you will get the following output in the terminal −

The given string is: Perl Codes Can Be Difficult To Read
1 T characters in the string
0 X characters in the string

As shown in the output, the given string has 1 "T" and no "X" characters. Note that we are searching for capital letters only.

Searching for Multiple Characters in a Perl String

In the above two examples, we explored the case where we would want the occurrence of a single character in a string. In this example, we would explore how to search multiple characters.

Example

Consider the code shown below. Here, we have a string with some positive and negative numbers. We will find out how many negative numbers are there in the given string.

$someString = "-9 57 48 -2 -33 -76 4 13 -44";
print "The given string is: ", $someString;
print "\n";
while ($someString =~ /-\d+/g) {
   $negativeCount++
}
print "There are $negativeCount negative numbers in the string.";

Output

If you run the above code in a Perl compiler online, you will get the following output in the terminal −

The given string is: -9 57 48 -2 -33 -76 4 13 -44
There are 5 negative numbers in the string.

Conclusion

In this tutorial, we used multiple examples to show how you can count the number of matches in a Perl string.