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Sunday, July 9, 2017

Random Libref macro function

Certain SAS procedures such as PROC DATASETS show examples with fixed library references or librefs such as source and dest as follows:

   proc datasets library = source ;
      copy out = dest ;
   run ;

A libref is 1 to 8 characters long, begins with a letter or underscore and contains only letters, numbers or underscores. If you use the SAS dictionary tables you will see that all libnames are stored in upper case.

What if the popularly named librefs of SORUCE and/or DEST are already in use and are not defined in metadata? Since a libref is simply a pointer to a folder (used by Windows and Linux), why not use a random value assigned to a macro variable to avoid any conflicts? The below macro function named %uuidgenlibref() does just that.

The SAS UUIDGEN() function returns a universally unique identifier (UUID) also know as a globally unique identifier (GUID) that looks like this: 83a6f563-67ee-2a47-8498-8f8dc706d0db. As you can see, the first character starts with an 8 which would violate the libref requirement to start with a letter. Here is an example of generating 10 UUIDs from a DO loop:

According to Wikipedia, "In its canonical textual representation, the sixteen octets of a UUID are represented as 32 hexadecimal (base 16) digits, displayed in five groups separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters (32 alphanumeric characters and four hyphens)."

The macro appends the first seven characters from the UUIDGEN() function using the SUBSTR() function to the 'X' prefix. Here is an example:

   %let sourcelibref = %uuidgenlibref() ;
   %let destlibref = %uuidgenlibref() ;

   libname &sourcelibref. "/lev1/abc" ;
   libname &destlibref. "/lev1/def" ;
 
   proc datasets library = &sourcelibref. ;
      copy out = &destlibref. ;
   run ;

   libanme &sourcelibref. clear ;
   libname &destlibref. clear ;   

The source consists of a single line of code as you can see below.

/**************************************************************************
*     Program: uuidgenlibref.sas
*      Author: Tom Bellmer
*     Created: 09Jul2017
*     Purpose: Creates an upper case 8 character libref
*       Usage: %put %uuidgenlibref() ;
**************************************************************************/
%macro uuidgenlibref() ; 
   X%upcase( %substr( %sysfunc( uuidgen() ), 1, 7 ) ) 
%mend ; 
 
/*EOF: uuidgenlibref.sas */

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