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Learning Perl, 5th Edition
book

Learning Perl, 5th Edition

by Randal L. Schwartz, Tom Phoenix, brian d foy
June 2008
Beginner content levelBeginner
352 pages
11h 16m
English
O'Reilly Media, Inc.
Content preview from Learning Perl, 5th Edition

The Invocation Arguments

Technically, the invocation diamond operator isn’t literally looking at the invocation arguments—it works from the @ARGV array. This array is a special array that is preset by the Perl interpreter as the list of the invocation arguments. In other words, this is just 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 just like any other array; you could shift items off of it, perhaps, or use foreach to iterate over it. You could even check to see if any arguments start with a hyphen, so that you could process them as invocation options (like Perl does with its own -w option).[]

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";
}

[] C programmers may be wondering about argc (there isn’t one in Perl), and what happened to the program’s own name (that’s found in Perl’s special variable $0, not @ARGV). Also, depending upon ...

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Publisher Resources

ISBN: 9780596520106Supplemental ContentErrata Page