I think you *need* to rewind the file by calling seek FH, 0, 0; in the subroutine find.
The file operation in Perl is ultimately linked to the underlying unix file handles. When you read from a Perl file handle, Perl uses and updates the underlying unix file handle, thus giving the side effect.
I think ideally you are looking for the Perl's equivalent to the C stdio's dup function, to duplicate/copy an existing file handle into a new file handle (not just an alias to the existing file handle, but a new independent file handle), and operate on the second file handle in the subroutine. I am not aware of such facility in Perl 5 (my lack of research perhaps), but I think Perl 6 has implimented the dup function for the File Object.
Update:
Ok, I just learned that you can duplicate a file handle in Perl with open NEW, "<&OLD";. I quickly came up with the following code -
#!/usr/bin/perl -w
use strict;
sub find {
local *IN = shift;
my $find_me = shift;
my $count = 0;
# duplicate existing file handle
open F2, '<&', *IN or die "Can not duplicate file handle";
my $tell = tell(F2);
while (<F2>) {
$count++ if (/$find_me/);
}
return "count: $count tell: $tell\n";
close F2;
}
open OUT, '>', 'tmp.txt' or die "$!\n";
print OUT while (<DATA>);
close OUT or die "$!\n";
open IN, 'tmp.txt' or die "$!\n";
print find( *IN, 'a' );
print find( *IN, 'a' );
print find( *IN, 'd' );
print find( *IN, 'e' );
__DATA__
a
a
a
c
d
e
The output is still -
#count: 3 tell: 0
#count: 0 tell: 13
#count: 0 tell: 13
#count: 0 tell: 13
That didn't work either! Ok, that taught me a lession - my assumption on the duplicated file handle could be wrong. I need some re-education.
Fellow monks, could you please tell me what is wrong with the duplicated file handle? Is perl actually creating a second independent file handle? Am I doing the right thing at all?
Thanks!
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[d/l]
[select] |
#...
my $pos=tell(FH);
#...
seek(FH,$pos,0);
return
The file handle duplicating thing looks interesting though...
update: fixed dumb semantic error
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Now if only you could localize a variable that represents the file position, you wouldn't have to manually save/restore its value. Hmmm....
package Tie::Scalar::FHPos;
use FileHandle;
sub TIESCALAR
{
my( $pkg, $fh ) = @_;
bless [$fh], $pkg;
}
sub FETCH
{
my( $self ) = @_;
$self->[0]->tell
}
sub STORE
{
my( $self, $pos ) = @_;
$self->[0]->seek($pos,0);
}
Test:
open F, "< foo.dat";
our $pos;
tie $pos, 'Tie::Scalar::FHPos', \*F;
{
local $pos = 20;
print "$pos: ", scalar(<F>);
}
print "$pos: ", scalar(<F>);
Cool!
jdporter
The 6th Rule of Perl Club is -- There is no Rule #6.
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[d/l]
[select] |
Update:
Ok, I just learned that you can duplicate a file handle in Perl with open NEW, "<&OLD";. I quickly came up with the following code -
From a Linux man page...
After successful return of dup or dup2, the old and new descriptors may be used interchangeably. They share locks, file position pointers and flags; for example, if the file position is modified by using lseek on one of the descriptors, the position is also changed for the other.
| [reply] |
The file operation in Perl is ultimately linked to the underlying unix file handles. When you read from a Perl file handle, Perl uses and updates the underlying unix file handle, thus giving the side effect.
Well not on windows, or other non-unix operating systems ....
| [reply] |
Besides what Roger said, if this is all what you want to do, you can:
use Data::Dumper;
use strict;
use warnings;
my @lines = <DATA>;
my $count = {};
map {chomp;$count->{$_} ++} @lines;
print Dumper($count);
__DATA__
a
a
a
c
d
e
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[d/l] |
