Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?)

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

Hi,

I'm using someone else's code which opens a file for reading like so:

$fh = do {local *FH};
open ($fh, $filename)
[download]

I'd never seen that trick before. I found an explanation here: http://perl.plover.com/local.html#3_The_First_Class_Filehandle_Tr.

I want to be able to report the last line number read. I could use $., but I thought IO::Handle's input_line_number method would be better (so I don't have to worry about whether this filehandle was the last one accessed).

However, IO::Handle seems not to like the "do {local *FH};" trick. Here's a small example:

use strict;
use warnings;

use IO::Handle;
my $fh;
# $fh = do {local *FH};   #bad
open ($fh, './test') or die("open failed: $!");
print "line: " . $fh->input_line_number();

__END__

output with "#bad" commented out:
line: 0

output with "#bad" included:
Can't call method "input_line_number" without a package or object refe
+rence at test line 10.
[download]

I have two easy workarounds -- use $. carefully, or modify the original code -- but I was wondering if there's a cleaner way of getting the line number?

Thanks,
Joe

Comment on Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) Select or Download Code

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Re: Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) by shmem (Chancellor) on Jun 07, 2007 at 21:04 UTC
Quick fix: make your $fh into an IO::Handle object: `# odd way to count lines of a file :-) use strict; use warnings; use IO::Handle; my $fh = IO::Handle->new; #good # $fh = do {local *FH}; #bad open ($fh, './test') or die("open failed: $!"); 1 while <$fh>; print "line: " . $fh->input_line_number(); __END__` [download] `$.` has its drawbacks - it contains the line number of last filehandle accessed. So there's no safe evaluation at a distance. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re: Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) by ysth (Canon) on Jun 08, 2007 at 05:53 UTC
You can't do $fh->input_line_number, but you can do (\$fh)->input_line_number.	[reply]
Re^2: Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) by naikonta (Curate) on Jun 08, 2007 at 06:18 UTC
I'm sorry, but I'm confused with your statement. $ perl -MIO::Handle -le 'open my $fh, "<", shift or die $!; print $fh- +>input_line_number while <$fh>' a_file_name 1 2 3 4 . . . $ perl -MIO::Handle -le 'open my $fh, "<", shift or die $!; print (\$f +h)->input_line_number while <$fh>' a_filename REF(0x99d7cdc) Can't call method "input_line_number" without a package or object refe +rence at -e line 1, <$fh> line 1. # $fh = do {local FH}; #bad $ perl -MIO::Handle -le 'my $fh = do {local FH}; open $fh, "<", shift + or die $!; print (\$fh)->input_line_number while <$fh>' a_file_name GLOB(0x846ccdc) Can't call method "input_line_number" without a package or object refe +rence at -e line 1, <FH> line 1. [download] Update: Added example code with "#bad" mark Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!	[reply] [d/l]
Re^3: Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) by ysth (Canon) on Jun 08, 2007 at 08:22 UTC
Always always always use warnings; teach your fingers to type -wle, not -le. You are doing (print(\$fh))->input_line_number there, not print((\$fh)->input_line_number).	[reply]
Re^4: Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) by naikonta (Curate) on Jun 08, 2007 at 08:42 UTC
Re^5: Last Line Read? (Any way to use IO::Handle methods on a "First-Class" Filehandle?) by ysth (Canon) on Jun 08, 2007 at 09:11 UTC


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