Perl's Special variable $^i

In the text processing often encounter this situation: there are a number of files need to modify the contents, but also want to retain the contents of the original file. This time Perl provides a handy variable $^i, after you save the suffix for the backup file in the variable, when we modify the contents of the file, Perl will: 1, first open the original file and save it as a backup file with the filename "suffix characters stored in the original filename +$^i". 2, in the original document modification. For example, in the following procedure, I'll change the ABC in all. Dat text to DFG and back up as a. bak file #!/usr/bin/perl-w use strict; $^i= ". Bak";   while (<>) {s/abc/dfg/g; Print }