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

Hi Monks,
I'm working on linux and win32 machines. This routine parses mostly big LOG files, often from the *other* OS. The files contain ether \r\n or \n as EOL and may not be changed.
I have written a routine, which uses Tie::File in RO mode to get the lines. But this proggy dies if it ties an single-element-array which happens when getting newline text while running under win32.
Any suggestions?

# $/ = "\x0d\x0a"   # this is default (OS = Win32)
tie my @array, 'Tie::File', $file, mode => O_RDONLY, memory => 0 or di
+e $!;   # ReadOnly und *no MemBuffer* !!
# $_ =~ s/\r?\n/\n/g for (@array);  # doesn't work because $file will 
+be written
$n_recs = @array;  # how many records/lines are in the file?
unless ($n_recs > 1) {
   untie @array;
   local $/ = "\x0a";
   tie @array, 'Tie::File', $datei, mode => O_RDONLY, memory => 0 or d
+ie $!;
   $n_recs = @array;
   print join ("~LF~", @array);   # test to see...
   die "Sorry -- only one line!\n" unless $n_recs > 1;
}

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Re: Problems with changing $/ and Tie::File in RO mode (:crlf)
by almut (Canon) on Oct 01, 2009 at 14:24 UTC

    As an alternative to your approach, you might want to look into PerlIO, in particular the :crlf layer, which is responsible for Perl's different handling of newlines on Windows vs. Unix:

    :crlf
    A layer that implements DOS/Windows like CRLF line endings. On read converts pairs of CR,LF to a single "\n" newline character. On write converts each "\n" to a CR,LF pair. (...)

    By default, that layer is active on Windows perls, but nothing is keeping you from using the layer on Unix to read Windows-style text files, or removing the layer on Windows to write Unix-style files.

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      Hi almut,
      you are right, this is interesting and I'm going to study on that, but does it also work with the 'Tie::File' to an @array? (If so, what do I have to code?)
      The advantage of 'Tie'ing in my way is to use zero memory, because I do not read the file into RAM.

[reply]
        does it also work with the 'Tie::File' to an @array?

        Yes.  For example, to read Windows-style files on Unix: 

        #!/usr/bin/perl

use Tie::File;

my $fname = shift @ARGV;

open my $fh_crlf, "<:crlf", $fname or die "Couldn't open '$fname': $!"
+;

tie my @array, 'Tie::File', $fh_crlf, mode => O_RDONLY, memory => 0 or
+ die $!;

for my $line (@array) {
    # ...
    # $line has no trailing \r
}

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