both @AND @@ TAILARING used for the hold the 
datalines,difference is how long they hold the data in the 
complilation process,@ hold the the data till the end of 
the line,but it release the dataline when it reach the end 
of the line, but @@ holds the datalines untill the end of 
the process

@@ is used when we have multiple observations per line of
raw data. It is used at the end of the INPUT statement. It
tells SAS to hold that line of data and continue to read
observations until it either runs out of data or reaches an
INPUT statement that does not end with a double trailing @.
When we use @ only without specifying n, SAS will hold that
line of data until it reaches either the end of the DATA
step or an INPUT statement that does not end with a trailing @. 

Both are line-hold specifiers; the difference is how long
they hold a line of data for input. The trailing @ holds a
line of data for subsequent INPUT statements, but releases
that line of data when SAS returns to the top of the DATA
step to begin building the next observation. The double
trailing @ holds a line of data for subsequent INPUT
statements even when SAS starts building a new observation.
In both cases, the line of data is released if SAS reaches a
subsequent INPUT statement that does not contain a line-hold
specifier.

@ is the pointer input that will hold the point at a
specific point variables inthe data

@@  is the on that may be useful to read the singleline of
raw data into multiple observations of the   sas data set.

syn

  data santhi;
   infile path;
      input var 1 2 3 4  @@;
         run;

@it holds the record at the end of the input statement or 
when the next input will come it will read the data.   and 
@ is also pointer controll .if we want to read particular 
character in a data set then we can use this @

@@ it is used for reading single line multiple 
observations.

These are those which works on the variable level by
default.It should appear and besides the variables in
sas.The columnpointers are
1)@
2)@@
@:the '@'is a column pointer which commands SAS to hold the
line strongly.The '@' is if it used,it is trailing of '@'
pointer.It reads only the first line across the available
variables data.

@@:It is used for the entire data from the external source
or internal by reading into a single variable.

both @AND @@ TAILARING used for the hold the 
datalines,difference is how long they hold the data in the 
complilation process,@ hold the the data till the end of 
the line,but it release the dataline when it reach the end 
of the line, but @@ holds the datalines untill the end of 
the process

@-is used to reading part of a rawdata file we using traling @
@@-is used to reading multiple observations of rawdata