Best way to check if argument is a filename or a file containing a list of filenames?

I'm writing a Perl script, and I'd like a way to have the user enter a file or a file containing a list of files in $ARGV[0].

The current way that I'm doing it is to ch开发者_StackOverflow中文版eck if the filename starts with an @, if it does, then I treat that file as a list of filenames.

This is definitely not the ideal way to do it, because I've noticed that @ is a special character in bash (What does it do by the way? I've only seen it used in $@ in bash).

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You can specify additional parameter on your command line to treat it differenly e.g.

perl script.pl file

for reading file's content, or

perl script.pl -l file

for reading list of files from file.

You can use getopt module for easier parsing of input arguments.

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First, you could use your shell to grab the list for you:

perl script.pl <( cat list )

If you don't want to do that, perhaps because you are running against the maximum command line length, you could use the following before you use @ARGV or ARGV (including <>):

@ARGV = map {
   if (my $qfn = /^\@(.*)/s) {
      if (!open(my $fh, '<', $qfn)) {
          chomp( my @args = <$fh> );
          @args
      } else {
          warn("Can't open $qfn: $!\n");
          ()
      }
   } else {
      $_
   }
} @ARGV;

Keep in mind that you'll have unintended side effects if you have a file whose name starts with "@".

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'@' is special in Perl, so you need to escape it in your Perl strings--unless you use the non-interpolating string types of 'a non-interpolating $string' or q(another non-interpolating $string) or you need to escape it, like so

if ( $arg =~ /^\@/ ) {
    ...
}

Interpolating delimiters are any of the following:

• "..." or qq/.../
• `...` or qx/.../
• /.../ or qr/.../

For all those, you will have to escape any literal @.

Otherwise, a filename starting with a @ has pretty good precedence in command line arguments.