Re: Variable Names and References

${"str$_"} is not a "hard" reference, it's a symbolic reference. i.e. it just refers to the name of a variable. You can't use symbolic refences while you have "strict refs" in use (as the error correctly states).

You can use symbolic references if you switch off "strict refs":

for (1..3) {
    no strict 'refs';
    my $ref = \${'str'.$_}; # this creates a hard reference VIA a symb
+olic reference
    # or:  my $ref = "str$_";  # this is a purely symbolic reference, 
+access is the same as above
    print "The string is $$ref"; 
}
[download]

update: you can only refer to GLOBALs with symbolic references. (update2: here's the relevant documentation in perlref) That's why that code still won't work. Here's a working version:

#!/usr/bin/perl -l

use warnings;
use strict;

our $str1 = qq[A-M o'Foo'];
our $str2 = qq[.,rtyu_''];
our $str3 = qq[$<%^];
our $str4 = qq[this works];

my $ref4 = \$str4;

print $$ref4;  # works as expected

for (1..3) {
    no strict 'refs';
    my $ref = \${'str'.$_};
    print "The string is $$ref"; 
}
[download]

Note that in your example using a simple array would be much easier, less error-prone and more efficient. Symbolic references are almost only useful these days for creating subroutines / packages at runtime (basically, wherever the only alternative is to use eval STRING).

updated again, added some comments

"What should it profit a man, if he should win a flame war, yet lose his cool?"

Comment on Re: Variable Names and References Select or Download Code

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Re^2: Variable Names and References by chakram88 (Pilgrim) on Mar 09, 2007 at 16:13 UTC
huh. Thanks. I understand what you mean about the symbolic reference. I just was not seeing it that way. (hence, while I understood the error message, I thought my problem was in the syntax, when all along it was improper referencing.) Thanks. And re your suggestion, I was going to go the route of an array -- but got hung up on why I couldn't make this work. Thank you, I can now stop floundering and get back to being productive.	[reply]
Re^2: Variable Names and References by rvosa (Curate) on Mar 12, 2007 at 00:52 UTC
`# or: my $ref = "str$_"; # this is a purely symbolic reference, +access is the same as above` [download] I don't see how that is a symbolic reference? I think this is (had to think a while to come up with something contrived, here): `my $class = 'CGI'; my $version; { no strict 'refs'; $version = ${"${class}::VERSION"}; use strict; } print $version # e.g. 3.05 on my machine` [download] In other words, we construct a variable's name ($CGI::VERSION) out of expanded variables ($class), and expand (it's almost like a string eval()) the result in turn to return the value stored under the constructed variable's name. ...mmmm still not really put elegantly, sorry.	[reply] [d/l] [select]
Re^3: Variable Names and References by Joost (Canon) on Mar 12, 2007 at 10:25 UTC
Symbolic references are just names of global variables. That means "str2" is a symolic reference, just like "CGI::VERSION" is. In other words; `"${class}::VERSION";` is a symbolic reference, and `${"${class}::VERSION"};` derefences the reference into the value of $CGI::VERSION. Note that "hard" references use exactly the same syntax to dereference. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]