Re: Localization gotcha?

The special variable '$.' is convenient when you want a quick way to detect the line number of the currently read file. But it can get a little confusing when you're dealing with multiple input files. In such cases, it might be advisable to take advantage of the added control and comfort of an object-oriented interface to filehandles such as that provided by IO::File.

IO::File inherits from IO::Handle and IO::Seekable. And one of the methods of IO::Handle is: input_line_number(), which happens to be an object-encapsulated substitute for '$.', but benefitting from all the scoping that applies to object instances.

A usage example:

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

{
    my $fh = IO::File->new( '< filename.txt' );
    if( defined $fh ) {
        while( my $line = <$fh> ) {
            print $fh->input_line_number(), 
                  ":\t",
                  $line;
        }
    }
}   # As $fh falls out of scope it is closed automatically.
[download]

It seems that input_line_number() is probably somewhat of a misnomer. Given that the input record separator needn't be '\n', the method would probably be better named input_record_number(), but that's just water under the bridge. :)

Dave

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Re: Localization gotcha? by benizi (Hermit) on May 19, 2005 at 19:38 UTC
Thanks for the suggestion, though I solved my actual problem per the response below (localizing $. wherever my module performed a seek() or used <>). Instead of using IO::File as you propose, since open()'ed files are automatically IO::Handles, you can just "use IO::Handle;" to provide the input_line_number method (note the continue): `use strict; use warnings; use IO::Handle; while (<>) { my $lineno = ARGV->input_line_number; # print a status message every 100 lines warn "Processing $ARGV line $lineno\n" unless $lineno % 100; # do some processing stuff } continue { close ARGV if ARGV->eof; # else input_line_number won't reset per- +file }` [download] (Update:) s/eof/ARGV->eof/ in the code example. (else a poorly written function, like my original seeky() would let the eof refer to the wrong file)	[reply] [d/l]

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Re: Localization gotcha?
by benizi (Hermit) on May 19, 2005 at 19:38 UTC

Thanks for the suggestion, though I solved my actual problem per the response below (localizing $. wherever my module performed a seek() or used <>).

Instead of using IO::File as you propose, since open()'ed files are automatically IO::Handles, you can just "use IO::Handle;" to provide the input_line_number method (note the continue):

use strict;
use warnings;
use IO::Handle;

while (<>) {
    my $lineno = ARGV->input_line_number;
    # print a status message every 100 lines
    warn "Processing $ARGV line $lineno\n" unless $lineno % 100;
    # do some processing stuff
} continue {
    close ARGV if ARGV->eof; # else input_line_number won't reset per-
+file
}
[download]

(Update:) s/eof/ARGV->eof/ in the code example. (else a poorly written function, like my original seeky() would let the eof refer to the wrong file)

[reply]
[d/l]