5.3. The Invocation ArgumentsTechnically, the diamond operator isn't looking at the invocation argumentsit works from the @ARGV array. This array is a special array preset by the Perl interpreter as the list of the invocation arguments. In other words, this is like any other array, (except for its funny, all caps name), but when your program starts, @ARGV is already stuffed full of the list of invocation arguments.[]
You can use @ARGV like any other array; you can shift items off of it or use foreach to iterate over it. You could even check to see if any arguments start with a hyphen, so you could process them as invocation options (like Perl does with its own -w option).[Dagger;]
The diamond operator looks in @ARGV to determine what filenames it should use. If it finds an empty list, it uses the standard input stream; otherwise, it uses the list of files that it finds. This means that after your program starts and before you start using the diamond, you've got a chance to tinker with @ARGV. For example, here we can process three specific files regardless of what the user chose on the command line: @ARGV = qw# larry moe curly #; # force these three files to be read while (<>) { chomp; print "It was $_ that I saw in some stooge-like file!\n"; } |