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How to replace the predefined variable which is set after the decleration

3 New Member
I have a hash , and in the value part of that (which is a string , So that variable interpolation can happen) i have used a variable .
Now later in the program i set this variable and try to substitute the value of it in the value of hash but it is returning null;

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  1. %Hash=('add'=> " test  $type ");
  2. $type = 1000;
  4. print " $Hash{$type};";
Aug 15 '09 #1
4 2412
3,509 Recognized Expert Moderator Specialist
You have to define the variable $type before you use it somewhere, otherwise, the place where its used will be filled with a null value.

My suggestion is that you add the following to the beginning of your script:

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  1. use strict;
  2. use warnings;
If you had them in place, you would have seen the following output to your screen:

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  1. Global symbol "%Hash" requires explicit package name at hashtest.pl line 20.
  2. Global symbol "$type" requires explicit package name at hashtest.pl line 20.
  3. Global symbol "$type" requires explicit package name at hashtest.pl line 21.
  4. Global symbol "%Hash" requires explicit package name at hashtest.pl line 23.
  5. Global symbol "$type" requires explicit package name at hashtest.pl line 23.
  6. Execution of hashtest.pl aborted due to compilation errors.
Also, this line:

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  1. print " $Hash{$type};";
is not correct. The first semi-colon needs to be rmoved so it looks like this:

Expand|Select|Wrap|Line Numbers
  1. print " $Hash{$type}";
Another issue is that $type is the value and the way you are referencing it is as if it were a key, so you will always get the following error:

Expand|Select|Wrap|Line Numbers
  1. Use of uninitialized value within %Hash in concatenation (.) or string at hashtest.pl line 24.
To have this code work the way you expect it, you will have to have it as follows:

Expand|Select|Wrap|Line Numbers
  1. use strict;
  2. use warnings;
  5. # Variables
  6. my $type = "1000";
  7. my %Hash=('add' => " test  $type ");
  10. #print " $Hash{$type}";
  11. print("$Hash{add}");
I hope this helps.


Aug 15 '09 #2
3 New Member
Thanks jeff ,
and print " $Hash{$type};"; was a typing mistake.

And what actually my problem is that i want to make the code more generic and to do that i use the variable inside the hash and i replace that variable at the runtime.

So, because of this reason i cant hard code the $type before the hash.

What i want is something like if i can some how refer to the variable and can change the value stored in that variable at the runtime .

Anyways thansk for the reply.
Aug 15 '09 #3
4,059 Recognized Expert Specialist
You can change the value of a variable, but not when it is used in a string. When you put a variable in a string its value replaces the variable, and then perl builds the string. The variable is not stored in the string only its value.
Aug 16 '09 #4
3 New Member
Thanks KevinADC for the reply..
Aug 16 '09 #5

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