Webmaster Forum / HTML, CSS, Scripts / JavaScript / November 2006

 #!/usr/bin/perl
 use strict;
 use warnings;
 $SIG{"ABRT"} = "something";
 print $SIG{"ABRT"};

It prints "main::something" and not "something".

Yes, they are. You can somewhat compare %ENV to the 'navigator'-object
in javascript until a certain level.

I would say they are both. %ENV is definitely an environmental
informant (hence its name), but %INC or %SIG are not, they hold other
kinds of information that the programmer might be interested in.

See example above with $SIG{"ABRT"}.

I would logically say that those associative arrays treat certain keys
differently simply because they are pre-defined.

He can overwrite the keys in question, only in his own program/scope,
but that's not recommended for obvious reasons.

 #!/usr/bin/perl
 use strict;
 use warnings;
 print $ENV{"SYSTEMROOT"} . "\n";
 $ENV{"SYSTEMROOT"} = "somethingelse";
 print $ENV{"SYSTEMROOT"};

says:

 C:\WINDOWS
 somethingelse

That is correct. And the general rule is to not modify them unless you
have a (very) good reason. I haven't seen any such case where that
would be desired though.

Well, the hashes in question are pre-existing and have a number of
pre-defined keys. You might reset the hash or do what you like with it.
But you should really try to avoid that, the purpose for their
existence is to read them out for whatever reason.

 #!/usr/bin/perl
 use strict;
 use warnings;
 while (my ($key, $value) = each %ENV)  {
   print "$key = $value \n";
 }

prints (for me):

 USERPROFILE = C:\Documents and Settings\DOT
 HOMEDRIVE = C:
 TEMP = C:\DOCUME~1\DOT\LOCALS~1\Temp
 SYSTEMDRIVE = C:
 PROCESSOR_REVISION = 0304
 SYSTEMROOT = C:\WINDOWS
 CLIENTNAME = Console
 COMMONPROGRAMFILES = C:\Program Files\Common Files
 COMSPEC = C:\WINDOWS\system32\cmd.exe
 SESSIONNAME = Console
 LOGONSERVER = \\BART
 APPDATA = C:\Documents and Settings\DOT\Application Data
 WINDIR = C:\WINDOWS
 PROGRAMFILES = C:\Program Files
 OS = Windows_NT
 PROCESSOR_LEVEL = 15
 PATHEXT = .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
 USERNAME = DOT
 PROMPT = $P$G
 NUMBER_OF_PROCESSORS = 1
 FP_NO_HOST_CHECK = NO
 HOMEPATH = \Documents and Settings\DOT
 PROCESSOR_IDENTIFIER = x86 Family 15 Model 3 Stepping 4, GenuineIntel
 PATH = c:\Perl\bin;C:\WINDOWS\system32;C:\WINDOWS
 USERDOMAIN = BART
 COMPUTERNAME = BART
 ALLUSERSPROFILE = C:\Documents and Settings\All Users
 PROCESSOR_ARCHITECTURE = x86
 CLASSPATH = .;
 TMP = C:\DOCUME~1\DOT\LOCALS~1\Temp

I can change every key and/or value, but that only effects %ENV as a
variable and not the 'real' environmental information that I got at the
start. Next time, or even next scope, %ENV will have the same
prepopulated key/values again. It differs from javascript where one
cannot change such predefined values. Instructions like, say,
navigator.appName = '1234'  are not accepted in javascript.

No, it applies to all variables - it's a simple mechanism. Perl modules
might behave the same as an external .js file in this regard. Variables
originating from external code can be exported to the main programme.