For those of you who actually took up the challenge and got started, you likely followed my blog through the summer. Not every article has been about Perl, but a good few have. The time has come for more.<\/p>\n Today’s article plugs an obvious hole in our knowledge base so far: getting user input. After all, it’s hard to interact with a program if you can’t give it different values to see how the output changes.<\/p>\n Perl has an array called @ARGV that is dedicated to storing inputs from the command line. (See my article on arrays here<\/a>.) The following program serves as an example:<\/p>\n The activity of this code is likely not mysterious. It is given the input array @ARGV with three values in it. $ARGV[0] is expected to contain your name; $ARGV[1] and $ARGV[2] should each contain a number. The program fetches your name from $ARGV[0], then stores it in the variable $name. Next, the program fetches the numbers from $ARGV[1] and $ARGV[2], stores them in $firstnumber and $secondnumber, adds the two, then stores the sum in $ans. On the command line, it gives you a friendly greeting by the name you gave, afterwards reminding you the numbers you gave and telling you their sum. Where you see \\n, the terminal will start a new line. That’s just done to make space on the screen for the output.<\/p>\n At this point, the serious reader might have four questions in mind:<\/p>\n <\/p>\n <\/p>\n <\/p>\n The answer is that you enter those inputs, in order, after the program name. Let’s imagine the program above is called lucy.txt<\/span>,and that your own name is Edward. Furthermore, you are just now wondering what the sum of 329 and 1982 is. Without a pencil or calculator handy, you’d like to call on lucy.txt<\/span> for the answer. First, you will go into the terminal (see my articles here, <\/a>here,<\/a> and\/or here<\/a>, depending on your operating system). Next, you will place yourself in the directory where lucy.txt<\/span> resides. Finally, you will call her and give her the three inputs by entering the following line:<\/p>\n perl lucy.txt Edward 329 1982<\/span><\/p>\n If all goes well, Lucy will answer with<\/p>\n Hello, Edward. You entered 329 and 1982. Their sum is 2311.<\/span><\/p>\n The very first line of lucy.txt<\/span>, specifically<\/p>\n #!\/usr\/bin\/perl<\/span><\/p>\n is called the shebang line. (You can read more about it here.<\/a>) It is needed in non-Windows environments. While it’s not necessary in Windows, it doesn’t seem to hurt if it’s there.<\/p>\n Good luck with this!<\/p>\n Source<\/em>: Robert Pepper’s Perl Tutorial<\/a><\/p>\n
\nBack on June 22,<\/a> I broached the idea of getting started with Perl. After all, I argued, academic pursuits can continue through the summer, the motivation being interest rather than preparing for an exam.<\/p>\n
\n#!\/usr\/bin\/perl
\n$name=$ARGV[0];
\n$firstnum=$ARGV[1];
\n$secondnum=$ARGV[2];
\n$ans=$firstnum + $secondnum;
\nprint “\\n\\nHello, $name.”;
\nprint ” You entered $firstnum and $secondnum.”;
\nprint ” Their sum is $ans\\n\\n.”<\/span><\/p>\n\n