[ruby-talk:04221] Re: getopt(s|long) and ARGF

Hugh Sasse Staff Elec Eng <[e-mail]> writes:

> How do the getopt libraries interact with ARGF?  I know they can remove
> things from ARGV, but will this mean that ARGF is affected at the same
> time?  I'm not sure from the information I have found.

ARGF used ARGV whenever it needs to: it is evaluated lazily. What this 
means is that whenever you do a gets, ARGF says "do I have a file to
read from?" If not, it picks the next thing off ARGV and uses it. For
example, here's som code that skips a file in the middle of ARGV.


     File.open("_f1", "w") {|f| f.puts "f1" }
     File.open("_f2", "w") {|f| f.puts "f2" }

     ARGV.shift while ARGV.length > 0

     ARGV <<  "_f1" << "gumby" << "_f2" 

     puts gets
     ARGV.shift   # skip gumby
     puts gets

And here it is again, changing the name of the next fil to open just
before it opens it.

     File.open("_f1", "w") {|f| f.puts "f1" }
     File.open("_f2", "w") {|f| f.puts "f2" }

     ARGV.shift while ARGV.length > 0

     ARGV <<  "_f1" << "gumby"

     puts gets
     ARGV.shift   # skip gumby
     ARGV << "_f2"
     puts gets


Hope this helps.


Dave