How can I use a Perl hash key that has a literal d

问题:

I have a hash in Perl which has been dumped into from some legacy code the name of the key has now changed from simply reqHdrs to reqHdrs.bla

$rec->{reqHdrs.bla}

My problem is now I cant seem to access this field from the hash any ideas? The following is my error

Download Script Output: Bareword "reqHdrs" not allowed while "strict subs" in use

回答1:

As described in perldoc perldata:

...An identifier within such curlies is forced to be a string, as is any simple identifier within a hash subscript. Neither need quoting. Our earlier example, $days{'Feb'} can be written as $days{Feb} and the quotes will be assumed automatically. But anything more complicated in the subscript will be interpreted as an expression. This means for example that $version{2.0}++ is equivalent to $version{2}++, not to $version{'2.0'}++.

In general, if you have a hash key with a character outside the [A-Za-z0-9_] range, use quotes (either single or double) inside the braces. As with normal strings, contents in double quotes will be parsed for any contained variables, while single quoted strings are taken literally:

use strict; use warnings;
use Data::Dumper;
my $x = 1;
my %hash = (
    bare_string => 'hi there',
    "not a bare string" => 'yup',
);
$hash{'$x'} = 'foo';
$hash{"$x"} = 'bar';
print Dumper(\%hash);

prints:

$VAR1 = {
      'bare_string' => 'hi there',
      'not a bare string' => 'yup',
      '$x' => 'foo'
      '1' => 'bar',
    };

回答2:

According to perldoc perldata that when an identifier is used within curlies, such as when accessing a hash value via a key, that identifier is assumed to be a string and is treated as such. Quotes will be assumed automatically, however, anything more complicated can be interpreted.

From perldata

In fact, an identifier within such curlies is forced to be a string, as is any simple identifier within a hash subscript. Neither need quoting. Our earlier example, $days{'Feb'} can be written as $days{Feb} and the quotes will be assumed automatically. But anything more complicated in the subscript will be interpreted as an expression. This means for example that $version{2.0}++ is equivalent to $version{2}++ , not to $version{'2.0'}++ .

Since the . is used for string concatenation, the interpreter I'm guessing is trying to concat those two strings together. Regardless it's always better to just use quotes to make it explicit, and if you have strict on it will probably throw a "bareword not allowed" error.

The solution to your problem:

$rec->{'reqHdrs.bla'}

回答3:

If the key is a string, just:

$rec->{"reqHdrs.bla"}

回答4:

Enclose the key in quotes:

$rec->{'reqHdrs.bla'}

回答5:

The bareword reqHdrs.bla is really just a... synonym, I guess, for a string. I'm not completely sure, but I think you should be able to simply use a string, e.g. 'reqHdrs.bla' as your key and that should retrieve your value OK.