EXIST Function

Verifies the existence of a SAS library member.

Category:

SAS File I/O

Syntax

EXIST(member-name<,member-type<, generation> > )

Required Argument

member-name

is a character constant, variable, or expression that specifies the SAS library member. If member-name is blank or a null string, then EXIST uses the value of the _LAST_ system variable as the member name.

Optional Arguments

member-type

is a character constant, variable, or expression that specifies the type of SAS library member. A few common member types include ACCESS, CATALOG, DATA, and VIEW. If you do not specify a member-type, then the member type DATA is assumed.

generation

is a numeric constant, variable, or expression that specifies the generation number of the SAS data set whose existence you are checking. If member-type is not DATA, generation is ignored.

Positive numbers are absolute references to a historical version by its generation number. Negative numbers are relative references to a historical version in relation to the base version, from the youngest predecessor to the oldest. For example, –1 refers to the youngest version or, one version back from the base version. Zero is treated as a relative generation number.

Details

If you use a sequential library, then the results of the EXIST function are undefined. If you do not use a sequential library, then EXIST returns 1 if the library member exists, or 0 if member-name does not exist or member-type is invalid.

Use the CEXIST function to verify the existence of an entry in a catalog.

Examples

Example 1: Verifying the Existence of a Data Set

This example verifies the existence of a data set. If the data set does not exist, then the example displays a message in the log:

%let dsname=sasuser.houses;
%macro opends(name);
%if %sysfunc(exist(&name)) %then
   %let dsid=%sysfunc(open(&name,i));
%else %put Data set &name does not exist.;
%mend opends;
%opends(&dsname);

Example 2: Verifying the Existence of a Data View

This example verifies the existence of the SAS view TEST.MYVIEW. If the view does not exist, then the example displays a message in the log:

data _null_;
dsname="test.myview";
   if (exist(dsname,"VIEW")) then
      dsid=open(dsname,"i");
   else put dsname 'does not exist.';
run;

Example 3: Determining If a Generation Data Set Exists

This example verifies the existence of a generation data set by using positive generation numbers (absolute reference):

data new(genmax=3);
   x=1;
run;
data new;
   x=99;
run;
data new;
   x=100;
run;
data new;
   x=101;
run;
data _null_;
   test=exist('new', 'DATA', 4);
   put test=;
   test=exist('new', 'DATA', 3);
   put test=;
   test=exist('new', 'DATA', 2);
   put test=;
   test=exist('new', 'DATA', 1);
   put test=;
run;

These lines are written to the SAS log:

test=1
test=1
test=1
test=0

You can change this example to verify the existence of the generation data set by using negative numbers (relative reference):

data new2(genmax=3);
   x=1;
run;
data new2;
   x=99;
run;
data new2;
   x=100;
run;
data new2;
   x=101;
run;
data _null_;
   test=exist('new2', 'DATA', 0);
   put test=;
   test=exist('new2', 'DATA', -1);
   put test=;
   test=exist('new2', 'DATA', -2);
   put test=;
   test=exist('new2', 'DATA', -3);
   put test=;
   test=exist('new2', 'DATA', -4);
   put test=;
run;