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grep function - Get only array elements that meet certain conditions

You can use the " grep function " to retrieve only the elements that match the conditions in the array. Each element of @array is passed to the default argument $_. Only elements that meet conditional statement will be added to @matched.

# Extract only the elements that match the conditions
@matched = grep {conditional statement} @array;

Example

This is an example to get only the elements that match regular expression. In this example, only integers are taken. If @nums is (1.23, 123, 43) then @matched will be (123, 43).

# Get only the elements that match the regular expression
my @nums = (1.23, 123, 43);
my @matched = grep {/^\d+$/} @nums;

If the pattern matching operator (=~ ) is omitted in the regular expression, the default variable $_ will be the target of pattern matching. The example above has the same meaning as:

# Explicitly specify the default variable $_
my @matched = grep {$_ =~ /^\d+$/} @nums;

This is an example to get only multiples of 2. If @nums is (1, 2, 3, 4) then @even is (2, 4).

# Get only multiples of 2
my @nums = (1, 2, 3, 4);
my @even = grep {$_ % 2 == 0} @nums;

Processing using grep can be written using foreach statement. Grep is often used in Perl because it is easier to write.

# for
my @nums = (1.23, 123, 43);
my @matched;
for my $num (@nums) {
  push @matched, $num if $num =~ /^\d+$/;
}

Reference "Array of Perl"

See below for a description of Perl's "arrays".

• Understand Perl's "arrays"