Derive unique libref and/or fileref in SAS - sas

Question

I often need to assign (and de-assign) temporary librefs/filerefs as part of utility macros - and thus I need to avoid naming conflicts with any existing librefs/filerefs. I know I could query the sashelp or dictionary tables and use conditional logic to iterate until I find one that isn't assigned, but I wondered if there was some easier way?
For instance, the following will create a uniquely named dataset in the work library:
data;run;
Is there some equivalent for librefs / filerefs?

Answer 1

The FILENAME() function already provides a method for this. When you call it with a missing value for the fileref it generates one using format #LNnnnnn.
6 data test;
7 length fileref $8 ;
8 rc=filename(fileref,,'temp');
9 put rc= fileref=;
10 run;
rc=0 fileref=#LN00056
NOTE: The data set WORK.TEST has 1 observations and 2 variables.
NOTE: DATA statement used (Total process time):
real time 0.02 seconds
cpu time 0.01 seconds
11 %global fileref ;
12 %let rc=%sysfunc(filename(fileref,,temp));
13 %put &=rc &=fileref ;
RC=0 FILEREF=#LN00058

Answer 2

The undocumented monotonic function, invoked in the open execution space, is very handy for obtaining an unused value.
libname mylib "C:\temp\sandbox";
data mylib.data%sysfunc(monotonic());
…
run;
Or code a macro to deliver a name for a libref. The macro can also check for existence if so desired:
%macro nextName(lib=,base=data,check=1);
%local index name;
%if %length(&lib) %then %let lib=&lib..;/* handle non-empty lib */
%do %until (&check and not %sysfunc(exist(&name,data)));
%let name = &lib.&base.%sysfunc(monotonic());
%end;
&name
%mend;
data data3;run;
data data4;run;
%put %nextName();
%put %nextName();
%put %nextName();
%put %nextName();
proc sort data=sashelp.class out=%nextname();
by age;
run;
You could go robust macro implementation and test for lib existence and valid check value.

Answer 3

The LIBNAME function has a similar feature as FILENAME but it does not populate the reference name variable as with FILENAME. The only way I can think of would be to compare SASHELP.VLIBNAM before and after. The librefs are in the form WC00000n.
79 data _null_;
80 length libref $32.;
81 libref = ' ';
82 rc = libname(libref,'.');
83 msg = sysmsg();
84 put _all_;
85 run;
libref= rc=-70004 msg=NOTE: Libref refers to the same physical library as WC000004. _ERROR_=0 _N_=1

Answer 4

actually writing one was fairly trivial, and didn't involve querying the (expensive) dictionary table:
libname mcore0 (work);
libname mcore1 (work);
libname mcore2 (work);
%macro mf_getuniquelibref(prefix=mcore,maxtries=1000);
%local x;
%let x=0;
%do x=0 %to &maxtries;
%if %sysfunc(libref(&prefix&x)) ne 0 %then %do;
%put Libref &prefix&x is available!;
&prefix&x
%return;
%end;
%end;
%put unable to find available libref in range &prefix.0-&maxtries;
%mend;
%let libref=%mf_getuniquelibref();
%put &=libref;
which returns;
UPDATE:
I've added macros for both of these to the MacroCore library and they can be utilised as follows:
filename mc url "https://raw.githubusercontent.com/sasjs/core/main/macrocore.sas";
%inc mc;
%let libref=%mf_getuniquelibref();
%let fileref=%mf_getuniquefileref();