Perl was designed to manipulate text files with very little programming effort. Our first Perl program should compare a list of abbreviations and then find the duplicates in that list. With duplicates we mean abbreviations that appear several times in the list. You can download the list here . The open function takes a file descriptor as first argument and the name of the file to read as second argument.
File descriptors are some kind of special variables.
You just put it in the open function, you use it in the function that reads out the data from the file and finally you give it to the close function. Traditionally file descriptors are written with all upper case letters in Perl. Perl has a number of implicit variables. These are variables which you did not declare. They are always there.