How to delete everything after the last character in a text file?

Question

Perl

Can you please tell me how to delete everything after the last character (.) in a text file using perl?
For example, there is a file 1.txt
In it:
gkjgklgn.jmnmmm.44444.55555.66666\hyjjkjmh
total should be:
gkjgklgn.jmnmmm.44444.55555

Answer 1

$string = "gkjgklgn.jmnmmm.44444.55555.66666\hyjjkjmh";
print substr($string, 0, rindex($string, "."));

Answer 2

And if the line "gkjgklgn.jmnmmm.44444.55555.66666\hyjjkjmh";
is in the file itself 1.txt
How to specify the file in the Perl script, and not the line?
Since the contents of the 1.txt file may change