This describes writing command-line processing for Perl scripts. Don't re-invent the wheel - this problem has been solved. Use Getopt::Long or a similar module from CPAN. This was presented as one of several "lightning talk" mini-presenations at the Silicon Valley Perl (SVPerl) meeting on Thursday, November 12, 2015 where the primary meeting topic was CPAN, the Comprehensive Perl Archive Network with the tag line "Your project is already half done".

1. Command Line Arguments
with Getopt::Long
By Ian Kluft
Part of short Lightning Talks session
Silicon Valley Perl
November 12, 2015
Santa Clara, California

2. Command-Line Arguments
● Many programs use command line interface
– Software builds
– Automated tools
– Experimental calculations
– Anything there isn't time to make a GUI
● Don't write new code to process CLI arguments
– Standards compliance comes with Getopt::Long
– It's in CPAN

3. Getopt::Long usage (1 of 2)
From the manpage:
use Getopt::Long;
my $data = "file.dat";
my $length = 24;
my $verbose;
GetOptions ("length=i" => $length, # numeric
"file=s" => $data, # string
"verbose" => $verbose) # flag
or die("Error in command line argumentsn");
● Note these things:
● Getopt::Long and its function GetOptions
● Initialization of variables before using them
● Specification and destination variable pairs

4. Getopt::Long usage (2 of 2)
● GetOptions processes the command line
● It removes the Unix-standard CLI options
– Like --optname, --optname=value, etc
– Single dash prefixes single-character options
– These can be in any order
● It leaves everything else in @ARGV list
– Such as filenames or text
– Whatever you use them for

5. Option specifications (1 of 2)
● GetOptions takes specification/destination pairs
– Specification: name/format of argument
– Destination: reference to variable to store data
● Boolean
– GetOptions ( “flag” => $flag );
– Stores true (1) if --flag is present
– With “!flag”, it stores false if --noflag is present
– $flag is not modified if --flag is not present
●
So don't forget to initialize it!

6. Option specifications (2 of 2)
● GetOptions ( “stringarg=s” => $stringarg );
– Use “=s” for mandatory string argument
– Use “:s” for optional string argument
● GetOptions ( “integerarg=i” => $integerarg );
– Use “=i” for mandatory integer argument
– Use “:i” for optional integer argument
● GetOptions ( “floatarg=f” => $floatarg );
– Use “=f” for mandatory floating point argument
– Use “:f” for optional floating point argument

7. Lists from arguments
● GetOptions ("library=s" => @libfiles);
– Multiple occurrences of --library go in @libfiles
● GetOptions ("library=s@" => $libfiles);
– Same thing, but $libfiles is a reference to an array
● Example: use the argument more than once
– prog --library lib/stdlib --library lib/extlib

8. Hashes from arguments
● GetOptions ("define=s" => %defines);
– key=value pair is placed in %defines hash
● GetOptions ("define=s%" => $defines);
– Same thing, except $defines is a ref to a hash
● Example:
– prog --define os=linux --define vendor=redhat

9. Similar CPAN modules
● Getopt::LL – wider set of prcoessing rules
● Getopt::XML – read XML in Getopt::Long style
● MooseX::Getopt – Getopt for Moose
● Many other smaller modules
– Search CPAN for “Getopt”