Getting file handle glob name instead of contents

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

I have been successfully reading files in a function for quite some time (see sample code snippet "WORKS" below). I am working on changing how I read the arguments that come into my function so that it is easier for other people to use. I tried changing to the use of a hash (see snippet "FAILS" below), but instead of getting the contents of the file that I opened, I get the glob address, e.g. GLOB(0x1499a8). I feel like the answer is right in front of me, but I still cannot see it. Can anyone help?

WORKS

#!/usr/bin/perl

my $handle1;
open($handle1, "< /tmp/1") || die "Input file does not exist.\n";

# Case 1
GetFileContentsViaScalar(\*$handle1);

close($handle1);

sub GetFileContentsViaScalar
{
  my $FH = shift;
  print "SHIFT:\n";
  {
    local($/);
    print <$FH>;
  }
}
[download]

FAILS

#!/usr/bin/perl

my $handle1;
open($handle1, "< /tmp/1") || die "Input file does not exist.\n";

# Case 2 -- fails
GetFileContentsViaFnHash(\*$handle1);

close($handle1);

sub GetFileContentsViaFnHash
{
  my %test;
  $test{FH} = shift;
  print "Function hash:\n";
  {
    local($/);
    print <$test{FH}>;
  }
}
[download]

Comment on Getting file handle glob name instead of contents Select or Download Code

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Re: Getting file handle glob name instead of contents by TGI (Parson) on Sep 10, 2008 at 18:08 UTC
Why are you passing typeglobs? There's no reason to use typeglobs here, just pass the lexical handle as a scalar. Plenty of older tutorials say to pass filehandles as globs, but that only applies to global filehandles generated when you do stuff like: `open( FOO, ">/bar/baz" )`. It's best to use a 3 argument version of open and a lexical handle. `#!/usr/bin/perl open(my $handle1, "<", "/tmp/1") or die "Input file does not exist.\n" +; # Case 2 -- fails GetFileContents($handle1); close($handle1); sub GetFileContents { my $foo = shift; print "Function hash:\n"; { local($/); print <$foo>; } }` [download] On a side note, I like to use the lower precedence or for error detection, becuase it won't mess with my lists if I leave off parens. See perlop section on C-Style Logical Or for more info. Update: Clarified globs vs typeglobs. Also, it's worth pointing out that using a lexical handle and not a typeglob doesn't resolve the issue with the `<$hash{lexical_handle}>` construct. Others have covered that issue. TGI says moo	[reply] [d/l] [select]
Re: Getting file handle glob name instead of contents by stevendel (Novice) on Sep 10, 2008 at 18:36 UTC
My apologies to all for not RTFM (or more precisely, not finding the relevant section to read). TGI, thanks for your additional remarks concerning passing scalars. I don't use global file handles any more, so passing just the scalar will work perfectly.	[reply]
Re: Getting file handle glob name instead of contents by Fletch (Bishop) on Sep 10, 2008 at 17:36 UTC
Quoth perlop: If what's within the angle brackets is neither a filehandle nor a simple scalar variable containing a filehandle name, typeglob, or typeglob reference, it is interpreted as a filename pattern to be globbed, and either a list of filenames or the next filename in the list is returned, depending on context. This distinction is determined on syntactic grounds alone. That means "<$x>" is always a readline() from an indirect handle, but "<$hash{key}>" is always a glob(). That's because $x is a simple scalar variable, but $hash{key} is not--it's a hash element. Even "<$x >" (note the extra space) is treated as "glob("$x ")", not "readline($x)". Your `$test{FH}` isn't a simple scalar variable so it's interpreted as a glob pattern. The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l]
Re: Getting file handle glob name instead of contents by Tanktalus (Canon) on Sep 10, 2008 at 17:41 UTC
The evil `<>` operator which tries to figure out if it's dealing with a filehandle or a glob operation ... you'll want to take a look at perlop for more details of how perl figures this out: If what’s within the angle brackets is neither a filehandle nor + a sim‐ ple scalar variable containing a filehandle name, typeglob, or +typeglob reference, it is interpreted as a filename pattern to be globbe +d, and either a list of filenames or the next filename in the list is returned, depending on context. This distinction is determined + on syn‐ tactic grounds alone. That means "<$x>" is always a readline() + from an indirect handle, but "<$hash{key}>" is always a glob(). That’s + because $x is a simple scalar variable, but $hash{key} is not--it’s a h +ash ele‐ ment. Even "<$x >" (note the extra space) is treated as "glob( +"$x ")", not "readline($x)". [download] You'll want to either do: `my $fh = $test{FH}; print <$fh>;` [download] or you'll want to: `use IO::Handle; print $test{FH}->getlines();` [download] Hope that helps,	[reply] [d/l] [select]