I'm building a hash, %student, whose key is a student ID, and whose value is a reference to an array of course descriptions of every course they've taken.

I want to print each student ID, and their course numbers ... and a lot of extra information about each course that can be found using the course number but is expensive to do.

Many students will have taken the same courses, and I only want to gather that extra information once per course. So I keep another hash, %catalog, whose key is the course number and whose value is "a lot of extra information that was expensive to gather". If exists $catalog{$course_number}, I needn't look up the extra information again.

Now I want for $student{$student_id} to be a reference to an array of references to the key/value pair stored at $catalog{$course_number}. I'm having a lot of trouble concocting the Perl grammar to create this. 

# if this course ID hasn't yet been added to the catalog
if (!exists $catalog{$course_id}) {    
   # add course ID and complex description to catalog
   $catalog{$course_id} = 1;           
}
# add a reference to the catalog entry to the student's course array
push @{$students{$student_id}}, \$catalog{$course_id};

[download]
When I look at %students in the debugger with the 'x' command, this is how it looks: 
0  10002538
1  HASH(0x1d3a850)
   'SCALAR(0x1d21458)' => 1
   'SCALAR(0x1d3a868)' => 1
2  681462925
3  HASH(0x1bcea58)
   'SCALAR(0x1010cc0)' => 1
   'SCALAR(0x1d21458)' => 1
   'SCALAR(0x1d215c0)' => 1
   'SCALAR(0x1d21608)' => 1
   'SCALAR(0x1d216f8)' => 1
   'SCALAR(0x1d3a868)' => 1
   'SCALAR(0x1d3ac70)' => 1

[download]
What I expected to be a course number is coming out 'SCALAR(0x1d3ac70)'.

(In the time it's taken to write this, it occurred to me I could store the course number, rather than a catalog reference, in the student's array of courses. But assuming there *might* be a reason to do it as I described, how do you do it?

In reply to How to make a reference to a hash cell by ibm1620

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