Hi c64whiz,

Some shells have ludicrously complex quoting/interpolation rules, so personally I'd avoid trying to re-implement them. If you really wanted to implement a simple subset of them though, there's Text::ParseWords, this is what Getopt::Long's GetOptionsFromString uses.

But I have the same question afoken already asked: why are you getting the command line on STDIN?

Here is a possible solution for applying getopts to a string:

use warnings;
use strict;

=head2 getopts_from_str(string, argumentspec, hashref)

This function uses L<Text::ParseWords>'s C<shellwords> to parse the
given I<string>, and then applies C<getopts> from L<Getopt::Std> to
the result, passing it the I<argumentspec> and I<hashref>.
If C<getopts> returns a true value, this function returns an arrayref
of the arguments remaining after applying C<getopts>,
and if C<getopts> reports an error by returning false,
this function also returns false.

=cut

use Text::ParseWords 'shellwords';
use Getopt::Std 'getopts';

sub getopts_from_str {
    my ($str,$argspec,$hashref) = @_;
    local @ARGV = shellwords($str);
    return unless getopts($argspec, $hashref);
    return [@ARGV];
}

# Example Code:
my $optstr = q{ -a "hello world" -b "some \"text\"" -c 'abc def' };
my $argv = getopts_from_str($optstr, 'a:b:c', \my %opts)
    or die "bad options";

use Data::Dumper;
print Dumper(\%opts, $argv);

__END__

$VAR1 = {
          'b' => 'some "text"',
          'a' => 'hello world',
          'c' => 1
        };
$VAR2 = [
          'abc def'
        ];
[download]

Update 2016-12-20: Since I've linked to this node a few times, I updated the above code so that it provides the function getopts_from_str. The original code follows.

Hope this helps,
-- Hauke D

I can answer part of the "why". (Probably not the OP's reason, though.)

A number of standard tools also take options from environment variables. E.g. less, gzip. This is a dubious practice, for sure. Less instructs the user to terminate any string args with a dollar sign '$' in that case. Gzip's handling of environment is still broken AFAIK was broken¹⁾. (It'll gladly read filenames, not just arguments—to a very comical effect when "GZIP=/bin/gzip" happens to be the case.)

The problem may also arise from attempting to bypass shell invocation for whatever reason.

1) Correction: this seems to be fixed in gzip version 1.7.

"getopt" will split @argv for you, and do the right thing.

perl -MGetopt::Std -E  'getopts("oif:"); say $_,"=",${"opt_$_"} for qw
+|o i f|' -- -o -f this 
o=1
i=
f=this
[download]

I want to have Getopt::Std parse a "command line" for me, but the "command line" is coming from STDIN.

Why? Usually, the shell (Unix, cygwin) or the C runtime (Windows, DOS, OS/2) handles command line parsing.

Alexander