Perl v5.25.7 added support for the @{^CAPTURE} variable which wrapped all the regexp parenthesis captures up into an array. If you need this functionality in a version of Perl older than that you can use this function:

my $str =  "Hello Jason Doolis";
$str    =~ /Hello (\w+) (\w+)/;

my @captures = get_captures(); # ("Jason", "Doolis")

sub get_captures {
    my $str      = $&;
    my @captures = ();

    # Build array using the offsets from @- and @+
    for (my $i = 1; $i < @-; $i++) {
        my $start = $-[$i];
        my $end   = $+[$i];
        my $len   = $end - $start;

        my $str = substr($str, $start, $len);
        push(@captures, $str);
    }

    return @captures;
}

I need to change some text in a file that's spread across multiple lines. This means perl -pE won't work because it treats each line as a separate regexp. Reading the file in to one big string and then running a multiline regexp is the best solution.

Using -0777 tells Perl to read the entire file in to one string and allows multi-line regexps to work as intended.

If you have an input file with the content like:

if (foo
    && bar && !true) {
    # Do stuff
}

You can change the if statement with a one-liner like this:

perl -0777 -pE 's/\(foo.*?\)/(test)/s' /tmp/input.txt

In a regular expression you can capture strings into variables using the default syntax:

$str = "2020-05-20";
$str =~ m/(\d{4})-(\d{2})-(\d{2})/;

printf("Year: %s Month: %s Day: %s\n", $1, $2, $3);

In a more complex regular expression/string things may move around. In this case it's better to use named captures instead of numeric captures. This can be done by using the (?<name>) syntax. This will capture that parenthesis pair in to the hash %+ with the name specified.

$str = "2020-05-20";
$str =~ m/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/;

printf("Year: %s Month: %s Day: %s\n", $+{year},$+{month},$+{day});

Using named captures you can easily update your regular expression if the position of elements in your string change.

Note: If you use named captures, Perl also populates the numeric equivalent.

I have an array of items that I want to do a quick regexp replace on each element. Here is a very elegant solution:

@names = ("John", "Paul", "george", "Ringo");
s/^g/G/g for @names;
print join(", ",@names);