On Jan 10, 2008 4:43 PM, Gunnar Hjalmarsson <[EMAIL PROTECTED]> wrote:
> Zembower, Kevin wrote:
> > I'm trying to write a program in which I have to make two passes through
> > the file. I want to call the file on the command line and process it
> > with 'while (<>){...'. Can I use something like 'seek STDIN, 0, 0'
> > between the two while loops to reset the diamond operator to the
> > beginning of the input file? I tried this but the program seemed to just
> > hang, waiting for input.
>
> You can do it by reopening ARGV after the first iteration:
>
> my $file = $ARGV[0];
> print "First time: $_" while <>;
> open ARGV, $file or die $!;
> print "Second time: $_" while <>;
>
> --
> Gunnar Hjalmarsson
> Email: http://www.gunnar.cc/cgi-bin/contact.pl
>
>
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>
>
That only works if filenames were passed in via the commandline, and
in that case it is better to use
my @input_files = @ARGV;
@ARGV = @input_files;
than a scalar that only captures the first item. If you try to use
the scalar when the <> operator is reading from STDIN you will get
Use of uninitialized value in open at t.pl line 8, <> line 9.
No such file or directory at t.pl line 8, <> line 9.
and when you use the array method it just won't read anything the
second time. There is no good, portable way that I know of to rewind
the standard input. If you really need to reuse the data then you
should save it to disk or to an array (depending on its size).
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