Please explain: A hash of file handles peculiarity

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

I'm looking for an explaination as to why this code fails, but a seemingly superfluous change makes it ok. This is broken

$file_h{$temp1} = "$temp2";
open($file_h{$temp1}, "< $file");
$line = <$file_h{$temp1}>;
[download]

However, if the last line is replaced by

$fh = $file_h{$temp1};
$line = <$fh>;;
[download]

then all is well. Ideas?

Comment on Please explain: A hash of file handles peculiarity Select or Download Code

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(tye)Re: Please explain: A hash of file handles peculiarity by tye (Sage) on Jan 30, 2001 at 10:00 UTC
The `<...>` operator can mean `...->readline()` or `glob("...")`. Perl has to decide which of those two you wanted. `<BAREWORD>` always means readline() as `glob("BAREWORD")` isn't very useful. `<.c>` always means glob() since ".c" isn't ever going to be a file handle. Now, things like `<$scalar>, <$array[0]>, <$hash{KEY}>` were harder to call. For some reason that I'm not completely sure of, it was decided that the first would always be readline() and all others would be glob(). I think this is generally acknowledged as not an ideal design decision, but we are stuck with it. So I tend to never use `<>` when I mean glob() and to write `$hash{KEY}->readline()` when my file handles aren't simple like `<FILE>` or `<$fh>`. I was surprised to find Perl smart enough to make this work even when I didn't create file handles with an IO::* module. I'm not sure how smart it is, though, so using a module is probably a good idea. - tye (but my friends call me "Tye")	[reply] [d/l] [select]
Re: Please explain: A hash of file handles peculiarity by japhy (Canon) on Jan 30, 2001 at 09:49 UTC
Perl demands that whatever appears inside the `<>` operator be a simple scalar value -- no subscripts or expressions allowed. You've "stumbled" upon a common workaround for this limitation. Another one would be to use a module like `IO::Handle` or `IO::File`, so that you can use the `readline` method of the objects instead. `japhy` -- Perl and Regex Hacker	[reply]
Re: Please explain: A hash of file handles peculiarity by repson (Chaplain) on Jan 30, 2001 at 09:49 UTC
The problem is based around the fact that the `< >` structure is used for globbing as well as reading. Therefore anything other than a simple variable or bareword, confuses perl. The solution (from memory) is to enclose the contents in braces or (slightly clearer) use the underlying function readline. `# $line = <$file_h{$temp1}>; $line = < {$file_h{$temp1}} >; $line = readline($file_h{$temp1});` [download]	[reply] [d/l] [select]