Handling Parameters

xorl has asked for the wisdom of the Perl Monks concerning the following question:

I've seen lots of scripts where you can invoke them with flags followed by parameters (hopefully that's the right terminology)like this:

./myscript.pl -a param_a -b param_b -d param_d -c param_c input1 input
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[download]

The problem is I don't know how to take that input and use it in the script. I know how to use @ARGV, but that would mean no flags and the params would have to be in the correct and same order every time.

The only solution I can think of right now is to loop through @ARGV.
Check if the value starts with a "-"
if it does then figure out which flag it is and assign the correct variable with the next value in @ARGV
if the value doesn't start with a "-" and the previous value doesn't either, then take that as normal input and proceed with the script.
if the value doesn't start with a "-" but the previous value does, then treat it as the value for that flag

Something about this just says to me there has to be a better way. Is there?

Thanks in advance

Edit: Big thanks to borisz for the first, most concise, and most useful answer. Thanks to everyone else as well.

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Re: Handling Parameters by borisz (Canon) on Jan 07, 2009 at 16:16 UTC
I use `Getopt::Long` or `Getopt::Std`. See: Getopt::Long and Getopt::Std Boris	[reply] [d/l] [select]
Re: Handling Parameters by zentara (Cardinal) on Jan 07, 2009 at 16:15 UTC
See Mixing command line arguments. You should probably use one of the Getopt modules. I'm not really a human, but I play one on earth Remember How Lucky You Are	[reply]
Re: Handling Parameters by properly (Monk) on Jan 07, 2009 at 16:17 UTC
Getopt::Long	[reply]
Re: Handling Parameters by jethro (Monsignor) on Jan 07, 2009 at 17:07 UTC
The right answer is naturally to use one of the Getopt modules as the previous posters said. If you want to know a better way in detail, your algorithm is a good starting point, just change it slightly: loop through @ARGV. Check if the value starts with a "-" if it does then figure out which flag it is and assign the correct variable with the next value in @ARGV. Step over both values if the value doesn't start with a "-" ~~and the previous value doesn't either~~, then take that as normal input and proceed with the script. ~~if the value doesn't start with a "-" but the previous value does, then treat it as the value for that flag~~ Instead of looping over the values you can shift them off the array, which makes the variable stepping much easier	[reply]
Re^2: Handling Parameters by wol (Hermit) on Jan 07, 2009 at 17:41 UTC
Given the effort that's embodied in the Getopt modules, I'd really recommend using them unless you have some obscure requirement that they just can't meet. Re-inventing this wheel (a "better way"?) is well worth avoiding. Still interesting from an academic perspective. Would anyone care to comment on how the Getopt modules are implemented? -- use JAPH; print JAPH::asString();	[reply]
Re^3: Handling Parameters by jethro (Monsignor) on Jan 07, 2009 at 17:53 UTC
"better way" than xorl's algorithm not "better way" than Getopt. Getopt::Std uses the algorithm I described, with shift.	[reply]