(even deadlier simple approach is noted at the end - ed).
How to read Perl command-line arguments
Submitted by alvin on May 22, 2011 - 7:37pm
Perl FAQ: How do I read command-line arguments in Perl (i.e., "Perl command line args")?
If you want to handle simple Perl command line arguments, such as filenames and strings, this tutorial is for you. If you want to handle command-line options (flags) in your Perl scripts (like "-h" or "--help"), this new Perl getopts command line options/flags tutorial is what you need.
Perl command line args and the @ARGV array
With Perl, command-line arguments are stored in a special array named
@ARGV. So you just need to read from that array to access your script's command-line arguments.
ARGV array elements: In the ARGV array,
$ARGV[0] contains the first argument,$ARGV[1] contains the second argument, etc. So if you're just looking for one command line argument you can test for $ARGV[0], and if you're looking for two you can also test for $ARGV[1], and so on.
ARGV array size: The variable
$#ARGV is the subscript of the last element of the @ARGVarray, and because the array is zero-based, the number of arguments given on the command line is $#ARGV + 1.Example 1: A typical Perl command line args example
A typical Perl script that uses command-line arguments will (a) test for the number of command line arguments the user supplied and then (b) attempt to use them. Here's a simple Perl script named "name.pl" that expects to see two command-line arguments, a person's first name and last name, and then prints them:
#!/usr/bin/perl -w
# (1) quit unless we have the correct number of command-line args
$num_args = $#ARGV + 1;
if ($num_args != 2) {
print "\nUsage: name.pl first_name last_name\n";
exit;
}
# (2) we got two command line args, so assume they are the
# first name and last name
$first_name=$ARGV[0];
$last_name=$ARGV[1];
print "Hello, $first_name $last_name\n";
This is fairly straightforward, where adding 1 to $#ARGV strikes me as the only really unusual thing.
To test this script on a Unix/Linux system, just create a file named name.pl, then issue this command to make the script executable:
chmod +x name.pl
Then run the script like this:
./name.pl Alvin Alexander
Or, if you want to see the usage statement, run the script without any command line arguments, like this:
./name.pl
Example 2: Perl command line arguments in a for loop
For a second example, here's how you might work through the command line arguments using a Perl for loop:
#!/usr/bin/perl
#---------------------#
# PROGRAM: argv.pl #
#---------------------#
$numArgs = $#ARGV + 1;
print "thanks, you gave me $numArgs command-line arguments:\n";
foreach $argnum (0 .. $#ARGV) {
print "$ARGV[$argnum]\n";
}
Running the example Perl command line program
To demonstrate how this works, if you run this Perl command line args program from a Unix command-line like this:
./argv.pl 1 2 3 4
or, from a DOS command-line like this
perl argv.pl 1 2 3 4
you'll get this result:
thanks, you gave me 4 command-line arguments: 1 2 3 4
As you can see, it prints all the command line arguments you supply to the Perl program.
------------------------------------------------------------------------------------------------------------
(or, an even simpler approach if you want it:
http://stein.cshl.org/genome_informatics/perl_intro/command_line.html
Processing Command Line Arguments
When a Perl script is run, its command-line arguments (if any) are stored in an automatic array called @ARGV. You'll learn how to manipulate this array later. For now, just know that you can call the shift function repeatedly from the main part of the script to retrieve the command line arguments one by one.
Printing the Command Line Argument
Code:
#!/usr/bin/perl # file: echo.pl $argument = shift; print "The first argument was $argument.\n"; ) |
'via Blog this'
