Generally, Perl reads data from a file which in the Perl program can be accessed using open and readline functions. However, for users who just want to test something for an urgent requirement, it is pretty boring to put the test data in a file and access it using the open and readline functions. The solution for this : __DATA__.
Let us consider a sample text file:
$ cat f1.txt AIX,1 Solaris,2 Unix,3 Linux,4