I saw this in a piece of code that I was reviewing today:

# first arguement is a -f; collect it and ignore it for now
my $optionalArgument = shift;

# get filename of the config file
my $configFile = shift;
[download]

In reply, I added this comment:

Eventually this should use one of the Getopt modules (like Getopt::Long - parsing the cmd line manually can lead to bugs, especially as code is refactored.

The response that I got back was essentially, "we use this method in a lot of our code - how can it lead to bugs?"

I rattled off a few of the advantages that sprang to mind:

• named params tend to be more flexible (it is easy to add params at a later date without risking breaking anything)
• named params are less error-prone because they are not order-dependent (e.g., shift)
• named params make it easier from the caller's perspective because they don't have to remember the exact order of the arguments
• meaningful param names aid memory and add clarity
• Getopt::Long provides basic parameter validation (required/optional/string/integer/etc)
• Getopt::Long makes it trivial to use flags and named params simultaneously

After looking back at the list, I realized that I was arguing for using named parameters and Getopt::Long - not explaining why parsing the command line manually is a Bad Idea.

I admit that my initial comment was more of a conditioned knee-jerk response than a well thought out reply. To be honest, I haven't really thought about it. I always use Getopt::Long when I need to parse the command line, but apparently I'm using it to gain several advantages, not to avoid disadvantages. Was I incorrect when I said "parsing the cmd line manually can lead to bugs"?

How do you parse the command line, and why? What are the risks for not using a module?

Thanks in advance for the input. pun intended ;-)

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