Perl Getopt and GetOptions

Two Perl modules (Getopt and Getoptions::Long) work to extract program flags and arguments much like Getopt and Getopts do for shell programming. The Perl modules, especially GetOptions::Long, are much more powerful and flexible.

Simple scripts show the power of these:

#!/usr/bin/perl
# script is "./g"
use Getopt::Std;
%options=();
getopts("od:fF",\%options);
# like the shell getopt, "d:" means d takes an argument
print "-o $options{o}\n" if defined $options{o};
print "-d $options{d}\n" if defined $options{d};
print "-f $options{f}\n" if defined $options{f};
print "-F $options{F}\n" if defined $options{F};
print "Unprocessed by Getopt::Std:\n" if $ARGV[0];
foreach (@ARGV) {
  print "$_\n";
}

Trying it out:

bash-2.05a$ ./g  -f -d F -o -F
-o 1
-d F
-f 1
-F 1
bash-2.05a$ ./g -o -d foo
-o 1
-d foo
bash-2.05a$ ./g -o rough -d foo
-o 1
Unprocessed by Getopt::Std:
rough
-d
foo
 

Processing of arguments stops when it saw "rough".

If you leave off a required argument, it just gets swallowed:

bash-2.05a$ ./g -d
bash-2.05a$ ./g -d foo
-d foo
 

But it's easily confused:

bash-2.05a$ ./g -d -o -f       
-d -o
-f 1
 

It thinks that -o is the argument of -d.

bash-2.05a$ ./g -k    
Unknown option: k
 

Like the simple shell "getopt", this complains when it gets an option that it doesn't know about. Unlike the shell "getopt", prefacing the option string with a ":" doesn't help. Instead, use "getopt":

#!/usr/bin/perl
# we'll call this one ./gg
use Getopt::Std;
%options=();
getopt("odfF",\%options);
print "-o $options{o}\n" if defined $options{o};
print "-d $options{d}\n" if defined $options{d};
print "-f $options{f}\n" if defined $options{f};
print "-F $options{F}\n" if defined $options{F};
 

Note the lack of any ":". This module doesn't care which flags take values and which don't: it assumes ALL of them take arguments.

The "getopt" isn't very bright:

bash-2.05a$ ./gg -f -o -d foo 
-d foo
-f -o
bash-2.05a$ ./g -f -o -d foo 
-o 1
-d foo
-f 1
 

But it doesn't complain:

bash-2.05a$ ./gg -l
bash-2.05a$ ./g -l
Unknown option: l

Unlike their shell cousins, neither of these have any issues with arguments containing spaces:

bash-2.05a$ ./g -o  -d "foo bar"          
-o 1
-d foo bar
bash-2.05a$ ./gg -o "foo"  -d "foo bar" 
-o foo
-d foo bar
 

Far better than either of these is the Getopt::Long module. Here's a script to play with it:

#!/usr/bin/perl
use Getopt::Long;
GetOptions("o"=>\$oflag,
            "verbose!"=>\$verboseornoverbose,
            "string=s"=>\$stringmandatory,
            "optional:s",\$optionalstring,
            "int=i"=> \$mandatoryinteger,
            "optint:i"=> \$optionalinteger,
            "float=f"=> \$mandatoryfloat,
            "optfloat:f"=> \$optionalfloat);
print "oflag $oflag\n" if $oflag;
print "verboseornoverbose $verboseornoverbose\n" if $verboseornoverbose;
print "stringmandatory $stringmandatory\n" if $stringmandatory;
print "optionalstring $optionalstring\n" if $optionalstring;
print "mandatoryinteger $mandatoryinteger\n" if $mandatoryinteger;
print "optionalinteger $optionalinteger\n" if $optionalinteger;
print "mandatoryfloat $mandatoryfloat\n" if $mandatoryfloat;
print "optionalfloat $optionalfloat\n" if $optionalfloat;

print "Unprocessed by Getopt::Long\n" if $ARGV[0];
foreach (@ARGV) {
  print "$_\n";
}
 

The hash array that this uses holds the argument name and the type of argument; what that points to is where it will store values for options processed.

Playing with it:

#
# doesn't care if it's -o or --o
bash-2.05a$ ./ggg -o
oflag 1
bash-2.05a$ ./ggg --o
oflag 1
#
# abbreviating is ok too
bash-2.05a$ ./ggg -verbose
verboseornoverbose 1
bash-2.05a$ ./ggg -verb   
verboseornoverbose 1
#
# but not this
bash-2.05a$ ./ggg -verbosity 
Unknown option: verbosity
#
# $verboseonoverbose will be 0 here
bash-2.05a$ ./ggg -noverb
#
# strings
bash-2.05a$ ./gggg -s    
Option string requires an argument
bash-2.05a$ ./ggg -s=foo
stringmandatory foo
bash-2.05a$ ./ggg -optional
bash-2.05a$ ./ggg -optional=foo
optionalstring foo
#
# ambiguity
bash-2.05a$ ./ggg --opt     
Option opt is ambiguous (optfloat, optint, optional)
#
# floats and integers
bash-2.05a$ ./ggg --optfloat=75.6
optionalfloat 75.6
bash-2.05a$ ./ggg --optint=75.6
Value "75.6" invalid for option optint (number expected)
bash-2.05a$ ./ggg --optint=75  
optionalinteger 75
bash-2.05a$ ./ggg -f --optfloat=75.6 -o
Value "--optfloat=75.6" invalid for option float (real number expected)
oflag 1
# once it runs out of options, it leaves @ARGV alone:
bash-2.05a$ ./ggg -o foo bar
oflag 1

Unprocessed by Getopt::Long
foo
bar

GetOpt::Long is obviously much more flexible. The hash you pass is a little clumsy, but if you think about it, there's no better way to do it. In some places, you might use something like this:

#!/usr/bin/perl
use Getopt::Long;
my %moo=();
GetOptions("o"=>\$moo{$oflag},
            "verbose!"=>\$moo{verbose},
            "string=s"=>\$moo{stringmandatory},
            "optional:s"=>\$moo{optionalstring},
            "int=i"=> \$moo{mandatoryinteger},
            "optint:i"=> \$moo{optionalinteger},
            "float=f"=> \$moo{mandatoryfloat},
            "optfloat:f"=> \$moo{optionalfloat});

foreach (keys %moo) {
 print "$_ = $moo{$_}\n";
}

print "Unprocessed by Getopt::Long\n" if $ARGV[0];
foreach (@ARGV) {
  print "$_\n";
}
 

but if you have so many flags that you are thinking that is helpful, your program is surely trying much too hard to be all things to all people.

Click here to add your comments
" but if you have so many flags that you are thinking that is helpful, your program is surely trying much too hard to be all things to all people."

Isn't that the philosophy behind Windows development?

After reading through all this, I said to myself, "One of these days I have to become an expert in Perl."

I have to admit that I'm much more likely to turn to a shell script or C to do a lot of the things that Perl would probably be better suited to doing. In many cases, a Perl program would certainly involve less work than writing and compiling a C program, and would undoubtably be more elegant and efficient than a typical shell script. However, as with using greenbar paper, old habits are hard to shake. I grok C and the shell, whereas I'm a rank amateur when it comes to Perl. One of these days...

--BigDumbDinosaur

The nice thing about Perl is that you don't have to be anything close to an expert to have it be helpful. If you know awk and sed and a little sh or ksh, you already understand a lot of Perl without even knowing it yet.

See http://aplawrence.com/Unixart/loveperl.html

--TonyLawrence



---September 18, 2004


I recently resumed perl programming after a ten year hiatus;
yup, just like riding a bike - I was really suprised how much perl lore lay dormant in the deep recesses of my aging brain. It has been a boon in refining a nascent automated java build framework I unexpectedly inherited. Combing ant, cruisecontrol, java, ksh, and perl, I was able to produce a flexible production grade build process in a matter of days... Getopts::Long was instrumental in enabling the central build.pl program to flexibly support any flavour of build one can imagine.
--Fleh

---February 10, 2005
SO how would I define the vars when I want to use-strict ? When I put it in I get:
Global symbol "$oflag" requires explicit package name at ./tester.pl line 5.
Global symbol "$verboseornoverbose" requires explicit package name at ./tester.pl line 6.
...etc. etc

Which is easy to fix with normal vars but I don't know how with references in this context! Help appreciated.

--Scary B.


---February 10, 2005

Just like usual:

my $oflag;
my $verboseornoverbose;

etc.

--TonyLawrence







Wed May 4 00:00:32 2005: Subject: Anyway to get rid of this warning?   Dave


test_opts2.pl -optional test
Use of uninitialized value in hash element at /home/dmckeon/scripts/test_opts2.pl line 11.
optionalstring = test

Program
**********************************************
#!/usr/bin/perl -w
# Option test dm


use strict;
use Getopt::Long;
my moo=();
my $oflag;


GetOptions("o"=>\$moo{$oflag},
"verbose!"=>\$moo{verbose},
"string=s"=>\$moo{stringmandatory},
"optional:s"=>\$moo{optionalstring},
"int=i"=> \$moo{mandatoryinteger},
"optint:i"=> \$moo{optionalinteger},
"float=f"=> \$moo{mandatoryfloat},
"optfloat:f"=> \$moo{optionalfloat});

foreach (keys moo) {
if ( defined $moo{$_} && exists $moo{$_}) {
print "$_ = $moo{$_}\n";
}
}

print "Unprocessed by Getopt::Long\n" if $ARGV[0];
foreach (@ARGV) {
print "$_\n";
}





Wed May 4 10:28:54 2005: Subject:   TonyLawrence


Don't use -w or define your variables. Simple as that.



Mon Sep 12 18:51:10 2005: Subject:   anonymous


-optional is the same as -o -p -t -i -o -n -a -l. You should use --optional.



Wed Jan 4 01:08:18 2006: Subject:   Kika


The reason is probably the typo where '$oflag' should be just 'oflag'.



Tue Dec 11 06:42:22 2007: Subject:   Gene


Uh. It's "GetOpt::Std" not "Getopt:Std" and "GetOpt::Long" not "Getoptions::Long"

You obviously never actually ran this code.

It is dishonest to publish something as "Information and Resources" that has blatant errors and is untested (and would never work).

In syntax, spelling is important.

Hope this helps,

Gene



Tue Dec 11 06:43:58 2007: Subject:   gene


heh. Ok. "Getopt" not "GetOpt" as I thought. Maybe I need to relax some... ;)



Tue Dec 11 11:44:24 2007: Subject:   TonyLawrence


Who never ran the code, Gene?

:-)

Hey, we all do make typo's, But I usually cut and paste from working code. Not that I can't screw it up later with editing, of course..

---

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---

Fri Jan 4 15:35:02 2008: Subject:   anonymous


do the vars have to be defined as:
my $oflag;
etc.....
I already have vars in a hash and when I try to do something like this:
GetOptions ( "root=r" => \$conf->{root},
"cl=c" => \$conf->{client_name});
I get this error:
Error in option spec: "root=r"
Error in option spec: "cl=c"








Fri Jan 4 15:49:52 2008: Subject:   TonyLawrence


Send me your actual code in email; I'll take a look at it..



Fri Jan 4 16:21:09 2008: Subject:   anonymous


Sorry I did not realize about the fees..Thanks Anyways.



Fri Jan 4 16:49:34 2008: Subject:   anonymous


I figured it out.... wrong option specifiers. Amazing how syntax plays so much into programming and without knowing the correct one will drive u crazy. Logic is overrated!! : )
Thanks



Tue Jul 8 17:01:11 2008: Subject: GetOptions is cool, what is the best way to handle defaults   Elden


This it my current method for handling 'default' values. Is there a cleaner way?

####### set up the defaults..........
my @file = ("CDN_DD.csv","PPDN_DD.csv");
my $unit =$ENV{"${pn}__LRU" } || "LSU_uP1";
my $numVarThresh =$ENV{"${pn}__PRINT_VAR_THRESH" } || 5;
my $w =$ENV{"${pn}__PRINT_VAR_WIDTH" } || -60;
my $na ="n/a";
my $help =0;
GetOptions( "lru=s" , \$unit
,"print_var_thresh=i" , \$numVarThresh
,"print_var_width=i" , \$w
,"na" , \$na
,"help" , \$help
);
if($help){usage();}
if(scalar(@ARGV)>0){@file=@ARGV;}

And how do you post <code> font to this site?





Thu Jul 2 09:50:58 2009: Subject:   hemant


Thanks for explanation by wonderful examples.

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