lgordoncurtis has asked for the wisdom of the Perl Monks concerning the following question:

This is related to the solution arrived at in my previous question: http://www.perlmonks.org/?node_id=462126 When using the FileHandle module, you can getpos() and setpos() the current position in the file. I can't figure out exactly what it is that getpos() returns, only that using its value accurately resets setpos(). Anyhow, I read in a line from a text file using this: 
 $mypos = $myhandle->getpos();
 $line = $myhandle->getline();

[download]
And then I want to find the first ; or / character in the line, and reset the position to that. I can find the index in $line of the character I'm looking for, but adding that to $mypos doesn't do what I thought it would do. Is there a way to convert that index into something I can add to $mypos and then use ->setpos($mypos)? Appreciate any help.

Replies are listed 'Best First'.
Re: FileHandle setpos function
by thundergnat (Deacon) on Jun 02, 2005 at 21:29 UTC

    Rather than getpos() and setpos(), I think you may have better luck with tell() and seek().

    Maybe this (very contrived) example will give you ideas.

    use strict;
use warnings;
use IO::File;
use IO::Seekable;

my $file = 'whatever.fil';

$/ =';';

my  $fh = new IO::File;
if ($fh->open("< $file")) {
    my $last = 0;
    while (<$fh>){
       if ($_ =~ m|([^/]+/)|){
           $fh->seek($last+$+[0],0);
           print $1,"\n";
       }else{
           print "$_\n";
       }
       $last = $fh->tell;
    }
    $fh->close;
}else{
    die "$file not found. $!\n";
}

    [download]

    Minor update to remove some unnecessary cruft.

[reply]
[d/l]
Re: FileHandle setpos function
by fishbot_v2 (Chaplain) on Jun 02, 2005 at 21:42 UTC

    See ->seek( pos, SEEK_CUR ) in IO::Seekable. You can record your reference position, grab the index, then setpos(), then SEEK_CUR (which take a relative scalar position).

    What getpos() returns is an opaque value that is meaningful only to setpos.

    All that said, it sounds like you are doing this the hard way. Building a parser with seek calls seems like... something that you don't really want to do.

    Update: minor correction

[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom