There are multiple ways to replace text in a file in Perl. Let's say example.txt contains the following lines of text.

apple
orange
grape
pineapple

I like to first store the content of the file in an array. In this example, the @fruit array will contain apple orange grape pineapple.

open(FH, "<", "/path/to/example.txt") or die "cannot open file $! \n";
my @fruit = <FH>;
close FH;

Then I use the map operator to update the array. In this example, "orange" is replace with "peach".

map { s/orange/peach/g } @fruit;

Then the file is overwritten to contain the values in the array.

my $file = "/path/to/file.txt";
open(FH, ">", "$file") or die "cannot open $file $! \n";

foreach my $line (@fruit) {
  print FH "$line";
}

close FH;