找到了用if

There a couple ways for 前五十条数据.
1) use firstobs option of infile statement
2) construct a count and when count reaches 50 then stop

148  data t1;
149    infile 'C:\temp\test.txt' firstobs=3;
150    input;
151    cnt=1;
152    if cnt=3 then stop;
153  run;

NOTE: The infile 'C:\temp\test.txt' is:
      Filename=C:\temp\test.txt,
      RECFM=V,LRECL=256,File Size (bytes)=15,
      Last Modified=20Aug2010:22:42:08,
      Create Time=20Aug2010:22:42:08

NOTE: 3 records were read from the infile 'C:\temp\test.txt'.
      The minimum record length was 1.
      The maximum record length was 1.
NOTE: The data set WORK.T1 has 3 observations and 1 variables.
NOTE: DATA statement used (Total process time):
      real time           0.01 seconds
      cpu time            0.00 seconds


154
155  data t1;
156    infile 'C:\temp\test.txt' ;
157    input;
158    cnt+1;
159    if cnt=4 then stop;
160  run;

NOTE: The infile 'C:\temp\test.txt' is:
      Filename=C:\temp\test.txt,
      RECFM=V,LRECL=256,File Size (bytes)=15,
      Last Modified=20Aug2010:22:42:08,
      Create Time=20Aug2010:22:42:08

NOTE: 4 records were read from the infile 'C:\temp\test.txt'.
      The minimum record length was 1.
      The maximum record length was 1.
NOTE: The data set WORK.T1 has 3 observations and 1 variables.
NOTE: DATA statement used (Total process time):
      real time           0.01 seconds
      cpu time            0.01 seconds

lz,希望下面的程序能有所帮助，仅供参考：

data a;
input x @@;
cards;
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
;
data b;
set a(firstobs=1 obs=5);/*取前5条记录*/
run;
data c;
set a(firstobs=16 obs=20);/*取后5条记录*/
run;