Perl 5.26, Strawberry on Windows I'm writing a parser to decode an options file effectively into perl-like assignments. A primitive config might look like:

@arr[2] = 5
var = 10

The example regex block is: 

sub parse_options {    # \%options_we_can_write, \@lines_of_options_fi
+le. [ $die_on_extra_options ] 
    #loads all matching values from an array of lines into the options
+ hash
    #uses '=' as the separator, one ( 1 ) space on either side
    my ($options_we_can_write, $options_file_lines, $die_on_extra_opti
+ons) = @_;
    
    my $var = "";
    my $sigil = "";
    my $val = "";
    my $setter = "";
    my $arraything = "";
    my $fd = "";
    my $rd = "";
    my $index = "";
    
    if( ! %{$options_we_can_write} ){ die "no options to match\n" }


    foreach ( @{ $options_file_lines } ){
        if( $_ =~ m/
                    ^([@%\$]?) # open sigil
                    ([a-zA-Z_]+) # variable
                    (\[)? #optional open bracket
                    ([\d]*) #optional number
                    (])? #optional close bracket
                    \ # space
                    = # equals
                    \ # space
                    ([a-zA-Z0-9_\\\/:]+)$ # string until end of line
                /x #end regex
            ){ #startif
            #print "##$1## ##$2## ##$3## ##$4## ##$5## ##$6##\n"; #com
+plains about undefined values

            if( defined ($sigil = $1) eq "" ){ $sigil = '$' }
            print "####sigil $sigil ##>$1<##\n";
            $var = $2;
            if( defined ($fd = $3) eq "" ){ $fd = "" };
            if( defined ($index = $4) eq "" ){ $index = "" }
            if( defined ($rd = $5) eq "" ){ $rd = "" };
            
            if ( ($fd eq '[' and $rd ne ']') or ($fd eq "{" and $rd ne
+ '}') ){
                print STDERR "Mismatched delimiters for $var, skipping
+\n";
                next;
            }
            
            if ( ($fd eq '[' and $rd eq ']') and ( ! is_whole_number($
+index) ) ){
                print STDERR "array assignment $var needs whole number
+ index\n";
                next;
            }
            
#            if ($fd eq "{" and $rd != '}' ){
#                print STDERR "Error bad delimiter for $var";
#            }


            $setter = "$sigil\{ \$options_we_can_write->{$var} }$fd$in
+dex$rd = $val";
            print "$setter\n";
            
            if( exists $options_we_can_write->{"$var"} ){
                eval $setter;            
            }
        
            next;
        }
    
    
    
    
    
        if( $_ =~ m/^(.*?) = (.*)$/ ){
            $var = $1;
            $val = $2;

            if( exists $options_we_can_write->{"$var"} ){
                ${ $options_we_can_write->{"$var"} } = $val;
            } else {
                print "Error: desired option $var not found\n";
            }
        }
        #print "$_\n";
    }
    return 0;
}

[download]
It's obviously in-work, but $1 seems to always be being set to "" if there's no match and not undef as the other values are. For example: 
if( defined ($fd = $3) eq "" ){ $fd = "" };

[download]
can be changed to: 
if( defined ($fd = $3) eq "" ){ $fd = "ssssssssss" };

[download]
and the ssssssss gets shown in 'print $setter' for an assignment without a front-delimiter. I first thought it was because I had "\$" vs '$' but that made no difference. If I explicitly assign $sigil right after the defined line it is assigned, but the else is never executed for $1, unlike $3 and $5. There are no extra characters being passed (\r, \n, etc)

In reply to Regex result being defined when it shouldn't be(?) by chenhonkhonk

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