How can I know if diamond operator moved to the next file?

Question

I have the following code in a file perl_script.pl:

while (my $line = <>) {
    chomp $line;
   // etc. 
}. 

I call the script with more than 1 file e.g.

perl perl_script.pl file1.txt file2.txt

Is there a way to know if the $line is started to read from file2.txt etc?

Answer 1

The $ARGV variable

Contains the name of the current file when reading from <>

and you can save the name and test on every line to see if it changed, updating when it does.

If it is really just about getting to a specific file, as the question seems to say, then it's easier since you can also use @ARGV, which contains command-line arguments, to test directly for the needed name.

---

One other option is to use eof (the form without parenthesis!) to test for end of file so you'll know that the next file is coming in the next iteration -- so you'll need a flag of some sort as well.

A variation on this is to explicitly close the filehandle at the end of each file so that $. gets reset for each new file, what normally doesn't happen for <>, and then $. == 1 is the first line of a newly opened file

while (<>) { 
    if ($. == 1) { say "new file: $ARGV" }
} 
continue { 
    close ARGV if eof;
}