Using backreferences

First a PHP example.

$string = "Hello to the World";
$string = eregi_replace("^.*(to) (the) World.*$","\\1 and \\2");
print($string); #> outputs "to and the"

In Perl, you use the =~ operator to start a RegExp. Below I have used it to get back references which can be used outside of the expression via in this case $1 and $2.

my $string = "Hello to the World";
$string =~ /^.*(to) (the) World.*$/;
print $string . " && the last two back references are |$1| and |$2|";

You can use the back references inside the string like below which is like the first PHP example.

my $string = "Hello to the World";
$string =~ s/^.*(to) (the).*$/$1 and $2/gi;

For more information, see in this document for Regular Expressions.

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