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Top Forums Shell Programming and Scripting Perl : How is file handling working here?? Post 302831873 by siddharthjindal on Friday 12th of July 2013 05:56:38 AM
Old 07-12-2013
Perl : How is file handling working here??

Hi,

I have a perl script which is just reading from the file but what I would like to understand is how the counter is moving without using the loop in the script.

Below are the details:
Code:
$ more /tmp/abc.txt
This is 0
This is 1
This is 2
This is 3
This is 4
This is 5
This is 6
This is 7
This is 8
This is 9

Script to read the above file is as :
Code:
$ more file1.pl
#!/usr/bin/perl
#
sub readfile
{
     my ($rec,$INFO);
     $INF=shift;
     if (defined($rec = scalar <$INF>))
     {
          print $rec;
     }
}
$file='/tmp/abc.txt';
open(xyz,$file);
$i=0;
$tes=readfile(xyz);
$tes=readfile(xyz);

when I am executing the above script, it is throwing the output as :

Code:
$ perl file1.pl
This is 0
This is 1

How counter in the file is moving to next row when I am not moving it and I am also not using any loops anywhere? I would just like to understand that? Does that mean loops are not required for moving through the file or I am getting it wrong somewhere?

Thanks in advance for any help on this!


Moderator's Comments:
Mod Comment Use code tags please, see PM.

Last edited by zaxxon; 07-12-2013 at 07:51 AM.. Reason: code tags and indention
 

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Plack::App::CGIBin(3pm) 				User Contributed Perl Documentation				   Plack::App::CGIBin(3pm)

NAME
Plack::App::CGIBin - cgi-bin replacement for Plack servers SYNOPSIS
use Plack::App::CGIBin; use Plack::Builder; my $app = Plack::App::CGIBin->new(root => "/path/to/cgi-bin")->to_app; builder { mount "/cgi-bin" => $app; }; # Or from the command line plackup -MPlack::App::CGIBin -e 'Plack::App::CGIBin->new(root => "/path/to/cgi-bin")->to_app' DESCRIPTION
Plack::App::CGIBin allows you to load CGI scripts from a directory and convert them into a PSGI application. This would give you the extreme easiness when you have bunch of old CGI scripts that is loaded using cgi-bin of Apache web server. HOW IT WORKS
This application checks if a given file path is a perl script and if so, uses CGI::Compile to compile a CGI script into a sub (like ModPerl::Registry) and then run it as a persistent application using CGI::Emulate::PSGI. If the given file is not a perl script, it executes the script just like a normal CGI script with fork & exec. This is like a normal web server mode and no performance benefit is achieved. The default mechanism to determine if a given file is a Perl script is as follows: o Check if the filename ends with ".pl". If yes, it is a Perl script. o Open the file and see if the shebang (first line of the file) contains the word "perl" (like "#!/usr/bin/perl"). If yes, it is a Perl script. You can customize this behavior by passing "exec_cb" callback, which takes a file path to its first argument. For example, if your perl-based CGI script uses lots of global variables and such and are not ready to run on a persistent environment, you can do: my $app = Plack::App::CGIBin->new( root => "/path/to/cgi-bin", exec_cb => sub { 1 }, )->to_app; to always force the execute option for any files. AUTHOR
Tatsuhiko Miyagawa SEE ALSO
Plack::App::File CGI::Emulate::PSGI CGI::Compile Plack::App::WrapCGI See also Plack::App::WrapCGI if you compile one CGI script into a PSGI application without serving CGI scripts from a directory, to remove overhead of filesystem lookups, etc. perl v5.14.2 2011-11-02 Plack::App::CGIBin(3pm)
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