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:

# script is "./g"
use Getopt::Std;
# 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:

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":

# we'll call this one ./gg
use Getopt::Std;
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:

use Getopt::Long;
            "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

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:

use Getopt::Long;
my %moo=();
            "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.

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© Tony Lawrence

" 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? <Grin>

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

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...


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.



---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 program to flexibly support any flavour of build one can imagine.

---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 "$oflag" requires explicit package name at ./ line 5.
Global symbol "$verboseornoverbose" requires explicit package name at ./ 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;



Wed May 4 00:00:32 2005: 441   Dave -optional test
Use of uninitialized value in hash element at /home/dmckeon/scripts/ line 11.
optionalstring = test

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

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

"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: 445   TonyLawrence

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

Mon Sep 12 18:51:10 2005: 1081   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: 1474   Kika

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

Tue Dec 11 06:42:22 2007: 3314   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,


Tue Dec 11 06:43:58 2007: 3315   gene

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

Tue Dec 11 11:44:24 2007: 3316   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..

Fri Jan 4 15:35:02 2008: 3388   anonymous

do the vars have to be defined as:
my $oflag;
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: 3389   TonyLawrence

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

Fri Jan 4 16:21:09 2008: 3391   anonymous

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

Fri Jan 4 16:49:34 2008: 3392   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!! : )

Tue Jul 8 17:01:11 2008: 4400   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(scalar(@ARGV)>0)[email protected][email protected];}

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

Thu Jul 2 09:50:58 2009: 6591   hemant

Thanks for explanation by wonderful examples.

Wed Feb 9 04:18:28 2011: 9288   PhilGoetz


I've used GetOpt::Long many times. I'm trying to use it on my Windows XP Cygwin system now, and it quite mysteriously will not run.

$ perl -e 'use GetOpt::Long; &GetOptions( "t=s" => $T)'
Undefined subroutine &main::GetOptions called at -e line 1.

$ cpan GetOpt::Long
CPAN: Storable loaded ok (v2.20)
Going to read '/home/brak/.cpan/Metadata'
Database was generated on Tue, 08 Feb 2011 22:42:11 GMT
Warning: Cannot install GetOpt::Long, don't know what it is.
Try the command

i /GetOpt::Long/

to find objects with matching identifiers.
CPAN: Time::HiRes loaded ok (v1.9719)

$ cpan

cpan shell -- CPAN exploration and modules installation (v1.9402)
Enter 'h' for help.

cpan[1]> i /GetOpt::Long/
CPAN: Storable loaded ok (v2.20)
Going to read '/home/brak/.cpan/Metadata'
Database was generated on Tue, 08 Feb 2011 22:42:11 GMT
Module = Getopt::Long (JV/Getopt-Long-2.38.tar.gz)
Module Getopt::Long::Descriptive (RJBS/Getopt-Long-Descriptive-0.089.tar.gz)
Module Getopt::Long::Descriptive::Opts (RJBS/Getopt-Long-Descriptive-0.089.tar.gz)
Module Getopt::Long::Descriptive::Usage (RJBS/Getopt-Long-Descriptive-0.089.tar.gz)
Module Getopt::Long::GUI (HARDAKER/Getopt-Long-GUI-0.1.tar.gz)
Module Getopt::Long::String (N/A)
Module Getopt::LongUsage (RGLAUE/Getopt-LongUsage-0.10.tgz)
Module POD2::IT::Getopt::Long (ENRYS/POD2-IT-Getopt-Long-1.02.tar.gz)
8 items found

cpan[2]> install GetOpt::Long
Warning: Cannot install GetOpt::Long, don't know what it is.
Try the command

i /GetOpt::Long/

to find objects with matching identifiers.
CPAN: Time::HiRes loaded ok (v1.9719)

Tue Feb 26 19:31:13 2013: 11912   spetry


What I had trouble finding documentation on is how to use Getopt::Long to use multiple flags for the same variable. Example: -host sets the same variable as -hostname, or -m sets the same name as -mac. Sure, I could use a hash or array to do the same thing, but this is a piece of specific code to populate a DB with data. Sometimes easier logic is required for debugging.

$IP ='';
$MAC = '';
$HOST = '';
$Serial = '';

's|serial=s', \$Serial,
'm|mac=s', \$MAC);

In the above, -n -host and -hostname will all populate the IP variable with the arg (-h is reserved if you are asking why "-n" instead of "-h"). Similarly, -m and -mac are identical for how GetOptions().

Tue Feb 26 20:46:45 2013: 11913   TonyLawrence



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