IO::Compress::Gzip blank output

shug94 has asked for the wisdom of the Perl Monks concerning the following question:

Hello Fellow Monks,

I am trying to compress a text file into gzip format using Perl.

I thought that the best way of doing so would be to use IO::Compress::Gzip. However I seem to be getting no useable output, can anyone tell me what I am doing wrong?

Here is my code:

use IO::Compress::Gzip;

#...

  my $localFilePath = 'C:/adi_vsfz/CTIP/transferFiles/20091015_Timetab
+le.txt';

  my $content;
  #Open a file handle to the file.
  if(open(FILE_TO_TRANSFER, $localFilePath))
  {
    my @transferFileContents = <FILE_TO_TRANSFER>;
    foreach(@transferFileContents)
    {
      $content .= $_;
    }

    close(FILE_TO_TRANSFER);

    my $newContent;
    IO::Compress::Gzip::gzip($content, $newContent);
    print("<BR><BR>\n".$content."<BR><BR>\n");
    print($newContent."<BR><BR>".length($newContent)."\n");
    if($newContent == undef)
    {
      print('$newContent is undef'."<BR>\n");
    }
  }
[download]

The output I get is:

Timetable Info


0 $newContent is undef
[download]

Any idea what I am doing wrong?

I hope you can help,

Cheers,

Shug

Comment on IO::Compress::Gzip blank output Select or Download Code

Replies are listed 'Best First'.
Re: IO::Compress::Gzip blank output by Gangabass (Vicar) on Sep 06, 2009 at 06:39 UTC
First always start your programs with this two lines: `use warnings; use strict;` [download] And second always check results of `open`...	[reply] [d/l] [select]
Re^2: IO::Compress::Gzip blank output by shug94 (Sexton) on Sep 06, 2009 at 23:36 UTC
I am using use strict, but I will add use warnings and see what that gives me. I am also checking the result of open, I just copied a snippet of my code to make it clearer.	[reply]
Re: IO::Compress::Gzip blank output by Sewi (Friar) on Sep 06, 2009 at 12:11 UTC
You may want to check the return value from IO::Compress::Gzip::gzip and maybe $! and $@. Personally, I prefer Compress::Zlib which is also doing Gzip, but this shouldn't make any differenct for your problem.	[reply]
Re: IO::Compress::Gzip blank output by graff (Chancellor) on Sep 07, 2009 at 02:46 UTC
You could also try a much simpler method, involving PerlIO::gzip: `#!/usr/bin/perl use strict; use warnings; use PerlIO::gzip; my $Usage = "Usage: $0 filename-to-compress\n"; die $Usage unless ( @ARGV == 1 and -f $ARGV[0] ); open( IN, "<", $ARGV[0] ) or die "$ARGV[0]: $!\n"; open( GZIP, ">:gzip", "$ARGV[0].gz" ) or die "$ARGV[0].gz: $!\n"; $/ = undef; $_ = <IN>; print GZIP;` [download] If you want to use this on an input file that is too big to fit in memory all at once, just use the normal I/O idiom with a while loop -- the result will be the same: `# $/ = undef; # leave $/ at it's default value... while (<IN>) { print GZIP; }` [download] UPDATE: (2010-10-18) It seems that PerlIO::gzip should be viewed as superseded by PerlIO::via:gzip. (see PerlIO::gzip or PerlIO::via::gzip).	[reply] [d/l] [select]
Re: IO::Compress::Gzip blank output by Burak (Chaplain) on Sep 07, 2009 at 00:27 UTC
The docs clearly state that parameters can not be bare scalars (unless they are file paths, which is not the case for you). Try this: `use IO::Compress::Gzip qw(gzip $GzipError) # other code... IO::Compress::Gzip::gzip(\$content, \$newContent) or die "gzip failed: + $GzipError\n"` [download] Also, you're doing the file slurp in a wrong and slow way: `my @transferFileContents = <FILE_TO_TRANSFER>; foreach(@transferFileContents) { $content .= $_; }` [download] It is possible to write this as: `$content = do { local $/; my $rv = <FILE_TO_TRANSFER>; $rv };` [download] which means: `$content = do { # minimize scope local $/; # make input separator undef 'till the end of this scope my $rv = <FILE_TO_TRANSFER>; # get all contents $rv # return it };` [download]	[reply] [d/l] [select]
Re^2: IO::Compress::Gzip blank output by shug94 (Sexton) on Sep 07, 2009 at 01:51 UTC
Thankyou very much! I will try using references instead. I have only been using Perl for three weeks, and I am getting the hang, but some things are still not clear. Thanks for helping out.	[reply]