Arguments are the values you pass to a Perl script. Each value on the command line after the name of the script will be assigned to the special variables$ARGV[0],$ARGV[1],$ARGV[2], and so on. The number of arguments passed to the script is stored in the$#ARGVvariable, and the full argument string is in the variable@ARGV. The name of the currently running program is stored in the$0variable.
Let’s try some examples working with arguments and other special variables. Create an executable script calledtestvars.plcontaining these lines:
#!/usr/bin/perl
print “My name is $0 \n”;
print “First arg is: $ARGV[0] \n”;
print “Second arg is: $ARGV[1] \n”;
print “Third arg is: $ARGV[2] \n”;
$num = $#ARGV + 1; print “How many args? $num \n”;
print “The full argument string was: @ARGV \n”;
Now if you run this script, here’s what you’ll see:
$./testvars.pl dogs can whistle
My name is testvars.pl
First arg is: dogs
Second arg is: can
Third arg is: whistle
How many args? 3
The full argument string was: dogs can whistle
Just a few notes about that example. I did say that the$#ARGVvariable contained the number of arguments, but I lied–sort of. Since the arguments are numbered starting at zero, you have to add one to the value of$#ARGVto get the actual number of arguments. It’s a bit weird, but if you’re a fan of the C language, it’ll all seem quite normal.
Also note that the@ARGVvariable doesn’t start with a dollar sign. That’s because it’s anarrayvariable, as opposed to the regularscalarvariables we’ve worked with so far. An array can be thought of as a list of values, where each value is addressed by a scalar (dollar sign) variable and an index number in square brackets, as in$ARGV[0],$ARGV[1], and so on. Don’t worry too much about arrays for now–that’s a topic for more study on your own.
