[Perl-beginners] Command line interface

Use GetOpt::Long or GetOpt::Std modules for processing command-line options.

- Rex

-----Original Message-----
From: Schooley, Chris
Sent: Tuesday, August 14, 2001 1:47 PM
To: '[email protected]'
Subject: Command line interface


I am working on a program that has users enter commands in a command line
interface. Is a giant switch / case statement the only way to structure a
program like this? There will probably be several hundred commands, some
with several arguments.

Thanks,

Chris Schooley

Forgot to send to the list...

-----Original Message-----
From: Schooley, Chris
Sent: Tuesday, August 14, 2001 10:53 AM
To: '[email protected]'
Subject: RE: Command line interface


Sorry, I should clarify - the program itself is like shell, has its own
commands, etc. It is intended to simulate the command line interface found
on various Cisco devices.

-----Original Message-----
From: [email protected]
Sent: Tuesday, August 14, 2001 10:47 AM
To: [email protected]
Cc: [email protected]
Subject: RE: Command line interface


Use GetOpt::Long or GetOpt::Std modules for processing command-line options.

- Rex

-----Original Message-----
From: Schooley, Chris
Sent: Tuesday, August 14, 2001 1:47 PM
To: '[email protected]'
Subject: Command line interface


I am working on a program that has users enter commands in a command line
interface. Is a giant switch / case statement the only way to structure a
program like this? There will probably be several hundred commands, some
with several arguments.

Thanks,

Chris Schooley

Based on this, I'm going to assume you have a set of commands that you're
checking thusly:

if ($command eq 'foo') {
do_foo();
} elsif ($command eq 'bar') {
do_bar();
} ...


What I typically do for problems like these is use a hash of hashes:

%commands = (
foo => {
sub => \&do_foo,
},

bar => {
sub => \&do_bar,
},
);

Then you simply do a lookup:

if ($commands{$command}) {
$commands{$command}{'sub'}->();
} else {
die("Unknown command name \"$command\".\n");
}


I use a hash of hashes, instead of a hash of name => subroutine pairs, so
that I can include other meta-data along with the command. For instance:

%commands = (
foo => {
sub => \&do_foo,
arguments => 2,
usage => '<arg1> <arg2>',
},

bar => {
sub => \&do_bar,
arguments => [0, 1],
usage => '[<optional arg1>]',
},
);

With this, you can do things like check the number of arguments specified
for the command, and if there aren't enough, or there are too many, print out
a usage message.


Michael

Right on! This is a much better way than I was considering.

"There is more than one way to do it"

Thanks,
Chris

-----Original Message-----
From: Michael Fowler
Sent: Tuesday, August 14, 2001 11:20 AM
To: Schooley, Chris
Cc: '[email protected]'
Subject: Re: Command line interface

Based on this, I'm going to assume you have a set of commands that you're
checking thusly:

if ($command eq 'foo') {
do_foo();
} elsif ($command eq 'bar') {
do_bar();
} ...


What I typically do for problems like these is use a hash of hashes:

%commands = (
foo => {
sub => \&do_foo,
},

bar => {
sub => \&do_bar,
},
);

Then you simply do a lookup:

if ($commands{$command}) {
$commands{$command}{'sub'}->();
} else {
die("Unknown command name \"$command\".\n");
}


I use a hash of hashes, instead of a hash of name => subroutine pairs, so
that I can include other meta-data along with the command. For instance:

%commands = (
foo => {
sub => \&do_foo,
arguments => 2,
usage => '<arg1> <arg2>',
},

bar => {
sub => \&do_bar,
arguments => [0, 1],
usage => '[<optional arg1>]',
},
);

With this, you can do things like check the number of arguments specified
for the command, and if there aren't enough, or there are too many, print
out
a usage message.


Michael