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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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readfile(1F)							   FMLI Commands						      readfile(1F)

NAME
readfile, longline - reads file, gets longest line SYNOPSIS
readfile filename longline [filename] DESCRIPTION
The readfile function reads filename and copies it to stdout. No translation of NEWLINE is done. It keeps track of the longest line it reads and if there is a subsequent call to longline, the length of that line, including the NEWLINE character, is returned. The longline function returns the length, including the NEWLINE character, of the longest line in filename. If filename is not specified, it uses the file named in the last call to readfile. EXAMPLES
Example 1: Typical use of readfile and longline Here is a typical use of readfile and longline in a text frame definition file: . . . text="`readfile myfile`" columns=`longline` . . . ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
cat(1), attributes(5) DIAGNOSTICS
If filename does not exist, readfile will return FALSE (that is, the expression will have an error return). longline returns 0 if a readfile has not previously been issued. NOTES
More than one descriptor can call readfile in the same frame definition file. In text frames, if one of those calls is made from the text descriptor, then a subsequent use of longline will always get the longest line of the file read by the readfile associated with the text descriptor, even if it was not the most recent use of readfile. SunOS 5.10 5 Jul 1990 readfile(1F)
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