Re: symbol table vs. eval

This will do what you want, I think:

my $test="my_variable_name";
my $default_value="the value I set";
$$test = "old value";
print "the value of \$my_variable_name = $my_variable_name\n";
$my_variable_name = "A new value";
print "the value of \$my_variable_name = $my_variable_name\n";
[download]

... but don't do that :)

Update: Perhaps I read & posted too quickly, does this do what you want?

my $test="my_variable_name";
my $default_value="the value I set";

$default_value = *$test;
$$default_value = "old value";

print "the value of \$my_variable_name = $my_variable_name\n";
$my_variable_name = "A new value";
print "the value of \$my_variable_name = $my_variable_name\n";
[download]

Update2: Thanks ikegami. You'll notice I omitted the obligatory "use strict;" and "use warnings;", because when they're not omitted:

$ perl symbol.pl
Global symbol "$my_variable_name" requires explicit package name at sy
+mbol.pl line 12.
Global symbol "$my_variable_name" requires explicit package name at sy
+mbol.pl line 13.
Global symbol "$my_variable_name" requires explicit package name at sy
+mbol.pl line 14.
Execution of symbol.pl aborted due to compilation errors.
[download]

--chargrill

$/  =  q#(\w)#  ;  sub  sig { print scalar reverse  join  ' ',  @_  } 
+ sig
map { s$\$/\$/$\$2\$1$g && $_ } split( ' ', ",erckha rlPe erthnoa stJu
+" );
[download]

Comment on Re: symbol table vs. eval Select or Download Code

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Re^2: symbol table vs. eval by raflach (Pilgrim) on Feb 23, 2006 at 18:49 UTC
A clear case of my overthinking the problem. Your first example does what I am needing. However I wonder if you can explain why the following occurs: Code: `package apackage; my $test="my_variable_name"; my $default_value="the value I set"; $$test = $default_value; print "the value of \$my_variable_name = $my_variable_name\n"; package main; $my_variable_name = "A new value"; print "the value of \$my_variable_name = $my_variable_name\n"; print "the value of the package variable = $apackage::my_variable_name +\n";` [download] Output: `the value of $my_variable_name = the value I set the value of $my_variable_name = A new value the value of the package variable = the value I set` [download] which works and is what I need, but... Code: `package apackage; my $test="my_variable_name"; my $default_value="the value I set"; our $$test = $default_value; print "the value of \$my_variable_name = $my_variable_name\n"; package main; $my_variable_name = "A new value"; print "the value of \$my_variable_name = $my_variable_name\n"; print "the value of the package variable = $apackage::my_variable_name +\n";` [download] Output: `Can't declare scalar dereference in our at -e line 5, near "$test =" Execution of -e aborted due to compilation errors.` [download]	[reply] [d/l] [select]
Re^3: symbol table vs. eval by ikegami (Patriarch) on Feb 23, 2006 at 18:59 UTC
You need to use `our $my_variable_name;` You may thing hardcoding the name is a problem, but it's not. The only reason you need `our` is because you hardcoded the name in the `print`. For example, `use strict; use warnings; package Hack; sub slash { my $var_ref = do { no strict 'refs'; \${'ExistingPackage::var'} }; $$var_ref = 'bar'; } package main; ExistingPackage->print_it(); Hack->slash(); ExistingPackage->print_it();` [download] whether ExistingPackage is `use strict; use warnings; package ExistingPackage; our $var = 'foo'; sub print_it { print("$var\n"); } 1;` [download] or `package ExistingPackage; $var = 'foo'; sub print_it { print("$var\n"); } 1;` [download]	[reply] [d/l] [select]
Re^4: symbol table vs. eval by raflach (Pilgrim) on Feb 23, 2006 at 19:23 UTC
yes but imagine the following situation include_file.pl (this is the only file I can edit) `my $test="my_variable_name"; # I pulled this from the db. I have no +idea what it actually is, plus I need to be able to support arbitrary + additions to the db anyway my $default_value="the value I set"; $$test = $default_value;` [download] module.pm (I can't touch this file) `use strict; package apackage; do "include_file.pl"; print "the value of \$my_variable_name = $my_variable_name\n"; # I can +'t control the fact that this variable is being referred to without i +ts package name` [download] script.pl (this is the code that will be run. I also can't touch it) `use strict; use module; $my_variable_name = "A new value"; print "the value of \$my_variable_name = $my_variable_name\n"; #print +the local value print "the value of the package variable = $apackage::my_variable_name +\n"; # print the package value` [download] The question is how do I while only modifying the include file avoid failing use strict. While still allowing the module file to access the variable by name directly and the script file to access it by package.	[reply] [d/l] [select]
Re^5: symbol table vs. eval by ikegami (Patriarch) on Feb 23, 2006 at 19:37 UTC
Re^3: symbol table vs. eval by chargrill (Parson) on Feb 23, 2006 at 19:03 UTC
Hrm. Note where I declare vars: `package apackage; my $test="my_variable_name"; my $default_value="the value I set"; $$test = $default_value; print "the value of \$my_variable_name = $my_variable_name\n"; package main; $my_variable_name = "A new value"; our $test; print "the value of \$my_variable_name = $my_variable_name\n"; print "the value of the package variable = $apackage::my_variable_name +\n";` [download] Yields: `the value of $my_variable_name = the value I set the value of $my_variable_name = A new value the value of the package variable = the value I set` [download] --chargrill `$/ = q#(\w)# ; sub sig { print scalar reverse join ' ', @_ } + sig map { s$\$/\$/$\$2\$1$g && $_ } split( ' ', ",erckha rlPe erthnoa stJu +" );` [download]	[reply] [d/l] [select]
Re^2: symbol table vs. eval by ikegami (Patriarch) on Feb 23, 2006 at 18:45 UTC
Caveat: Your solution won't work if `$my_variable_name` is a lexical (`my`) variable. It will only work if it's a package (`our`) variable.	[reply] [d/l] [select]
Re^3: symbol table vs. eval by raflach (Pilgrim) on Feb 23, 2006 at 18:51 UTC
I am working with package variables, so in this case I'm OK, but I do wonder why I can't declare it using 'our' (see my post below). Thanks!	[reply]
Re^2: symbol table vs. eval by ikegami (Patriarch) on Feb 23, 2006 at 18:53 UTC
Concerning your update, strict has nothing to do with it. If `use strict` is already present, so is either `our $my variable_name;` or `my $my variable_name;`. I was saying your code will only work with the former, not the latter. The OP's code (and the code in my reply) works with both.	[reply] [d/l] [select]