Re: Syntax error when trying to use a hash value as a file stream specifier

[kcott]

G'day Fireblood,

In the examples below, I've used a common alias of mine which picks up many problems:

$ alias perle
alias perle='perl -Mstrict -Mwarnings -Mautodie=:all -MCarp::Always -E
+'

Probably the first thing to note is that filehandles are globrefs. Here's an example (along with a hashref for comparison).

$ perle 'open my $fh, ">", "not_a_file"; say "$fh"; unlink "not_a_file
+";'
GLOB(0x8000c42e0)

$ perle 'my $hashref = {}; say "$hashref";'
HASH(0x800003bc8)

Had you used the strict pragma, you would have seen:

Bareword "STDERR" not allowed while "strict subs" in use ...

Always start your code with the following:

use strict;
use warnings;

or code that gives you one or both of those (e.g. use v5.12 gives you strict; use v5.36 gives you strict and warnings; various modules have similar effects):

The next question might be, what should you use instead of STDERR? I'd argue that \*STDERR is strictly correct as it's a globref; however, *STDERR will also work.

$ perle 'my $x = \*STDERR; say "$x";'
GLOB(0x80008fcd0)

$ perle 'my $x = *STDERR; say "$x";'
*main::STDERR

That finally brings us to how to use the hash value without an intermediate scalar value. You have two main options (perhaps others will suggest additional ones).

• As already mentioned by ++AnomalousMonk, continue to use "Indirect Object Syntax" and wrap the hash value in braces:

  $ perle 'my %fh = (err => \*STDERR); print {$fh{err}} "errmsg\n";'
  errmsg
  
  $ perle 'my %fh = (err => *STDERR); print {$fh{err}} "errmsg\n";'
  errmsg
  

• Use the hash value with the filehandle, and invoke print, say, and so on, as methods:

  $ perle 'my %fh = (err => \*STDERR); $fh{err}->print("errmsg\n");'
  errmsg
  
  $ perle 'my %fh = (err => *STDERR); $fh{err}->print("errmsg\n");'
  errmsg
  

Side note: All of the above examples were run using Perl v5.36. This version disables the indirect feature by default (see "perl5360delta: use v5.36"). Obviously, the filehandle case is still allowed; however, if you do use that syntax elsewhere (e.g. my $obj = new Class ...), you may want to consider getting out of the habit of doing so.