Probably best to leave the command-line parsing to the pros. Getopt::Long can handle almost all of these formats except for the first one, which I don't think is actually legal. But we can make it work:

#!/usr/bin/env perl

use strict;
use warnings;
use Getopt::Long qw(GetOptionsFromString :config gnu_compat :config pa
+ss_through);

foreach my $string (
    q{--rsync-path = 'blah blah'},                 # might be spaces b
+efore/after equal sign
    q{--rsync-path=/usr/bin/rsync},                # no quotes around 
+value (assuming this allowed by rsync)
    q{--rsync-path="blah blah \"blah"},            # double quotes, wi
+th possible escaped quotes
    q{--rsync-path='blah blah \'blah'},            # single quotes, wi
+th possible escaped quotes
    q{--rsync-path='blah blah' --another-option},  # additional option
+s might follow
    q{--another-option --rsync-path='blah blah'},  # additional option
+s precede
) {
    my $tidy_string = $string =~ s/(--rsync-path)\s*=\s*/$1=/r; # This
+ cleans up the whitespace around = in the first example.

    my $rsync_path;
    my ($ret, $args) = GetOptionsFromString(
        $tidy_string,
        'rsync-path=s' => \$rsync_path,
    );

    printf "%-48s: rsync_path => %-32s\n", "($string)" => "($rsync_pat
+h)";
}
[download]

The output:

(--rsync-path = 'blah blah')                    : rsync_path => (blah 
+blah)                     
(--rsync-path=/usr/bin/rsync)                   : rsync_path => (/usr/
+bin/rsync)                
(--rsync-path="blah blah \"blah")               : rsync_path => (blah 
+blah "blah)               
(--rsync-path='blah blah \'blah')               : rsync_path => (blah 
+blah \'blah)              
(--rsync-path='blah blah' --another-option)     : rsync_path => (blah 
+blah)                     
(--another-option --rsync-path='blah blah')     : rsync_path => (blah 
+blah)
[download]

I think that's correct handling for each of your examples.

The GetOptionsFromString subroutine was used, but if you're just parsing directly from the command line, GetOptions would have been adequate. The gnu_compat config option provides better handling for =, and the pass_through returns the un-handled options without noisy warnings.