How can I get the filename when using the <> Perl construct?

Question

Perl offers this very nice feature:

while ( <> )
{
    # Do something
}

...which allows the script to be used as script.pl <filename> as well as cat <filename> | script.pl.

Now, is there a way to determine if the script has been called in the former way, and if yes, what the filename was?

Answer 1

The variable $ARGV holds the current file being processed.

$ echo hello1 > file1
$ echo hello2 > file2
$ echo hello3 > file3
$ perl -e 'while(<>){s/^/$ARGV:/; print;}' file*
file1:hello1
file2:hello2
file3:hello3