I am reading the Perl Tutorial on Regex: https://perldoc.perl.org/perlretut.html
The piece of code uses "qw" in front of a list of dates.
When I use the "qw" code from the tutorial , I get an error.
I went digging
I found an example of what "qw" looks like ('data1' , 'data2' , ...) without "qw"

If I remove the "qw" and then single quote the data and separate with a comma ; it works.

See below code where I comment out the code:
for my $d ( '2006-10-21', '15.01.2007', '10/31/2005' ) - success
OR
for my $d qw( 2006-10-21 15.01.2007 10/31/2005 ) - error msg

The results for each run are shown - error or success

Included below is web page , a do a "find" and sys information

Why is "qw" not working for me?

###################################################################
#### the bad - use "qw" ###########################################
###################################################################
C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>> type zz.pl

print("\n ######################### \n");
    $fmt1 = '(?<y>\d\d\d\d)-(?<m>\d\d)-(?<d>\d\d)';
    $fmt2 = '(?<m>\d\d)/(?<d>\d\d)/(?<y>\d\d\d\d)';
    $fmt3 = '(?<d>\d\d)\.(?<m>\d\d)\.(?<y>\d\d\d\d)';

#   for my $d ( '2006-10-21', '15.01.2007', '10/31/2005' )
    for my $d qw( 2006-10-21 15.01.2007 10/31/2005 )
        {
        if ( $d =~ m{$fmt1|$fmt2|$fmt3} )
        {
            print "day=$+{d} month=$+{m} year=$+{y}\n";
        }
        }
[download]

C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>> zz.pl

syntax error at C:\Users\cash_\Documents\Perl\02 Learn 21 Days\zz.pl line 7, near "$d qw( 2006-10-21 15.01.2007 10/31/2005 )"
Execution of C:\Users\cash_\Documents\Perl\02 Learn 21 Days\zz.pl aborted due to compilation errors.

C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>>

###################################################################
######## the good - use single quotes (') around data #############
###################################################################

C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>> type zz.pl

print("\n ######################### \n");
    $fmt1 = '(?<y>\d\d\d\d)-(?<m>\d\d)-(?<d>\d\d)';
    $fmt2 = '(?<m>\d\d)/(?<d>\d\d)/(?<y>\d\d\d\d)';
    $fmt3 = '(?<d>\d\d)\.(?<m>\d\d)\.(?<y>\d\d\d\d)';

    for my $d ( '2006-10-21', '15.01.2007', '10/31/2005' )
#    for my $d qw( 2006-10-21 15.01.2007 10/31/2005 )
        {
        if ( $d =~ m{$fmt1|$fmt2|$fmt3} )
        {
            print "day=$+{d} month=$+{m} year=$+{y}\n";
        }
        }
[download]

C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>> zz.pl


#########################
day=21 month=10 year=2006
day=15 month=01 year=2007
day=31 month=10 year=2005

C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>>

###################################################################
######## from the web page #############
######## https://perldoc.perl.org/perlretut.html #############
######## do a find on "Named backreferences" #############
###################################################################
perlretut
Perl 5 version 26.1 documentation
Named backreferences
Perl 5.10 also introduced named capture groups and named backreferences.
To attach a name to a capturing group, you write either (?<name>...) or (?'name'...).
The backreference may then be written as \g{name} .
It is permissible to attach the same name to more than one group, but then only the leftmost
one of the eponymous set can be referenced. Outside of the pattern a named capture group is accessible through the %+ hash.

Assuming that we have to match calendar dates which may be given in one of the three
formats yyyy-mm-dd, mm/dd/yyyy or dd.mm.yyyy, we can write three suitable patterns
where we use 'd' , 'm' and 'y' respectively as the names of the groups capturing the
pertaining components of a date. The matching operation combines the three patterns as alternatives:

$fmt1 = '(?<y>\d\d\d\d)-(?<m>\d\d)-(?<d>\d\d)';
$fmt2 = '(?<m>\d\d)/(?<d>\d\d)/(?<y>\d\d\d\d)';
$fmt3 = '(?<d>\d\d)\.(?<m>\d\d)\.(?<y>\d\d\d\d)';
for my $d qw( 2006-10-21 15.01.2007 10/31/2005 ){
if ( $d =~ m{$fmt1|$fmt2|$fmt3} ){
print "day=$+{d} month=$+{m} year=$+{y}\n";
}
}

If any of the alternatives matches, the hash %+ is bound to contain the three key-value pairs.



###################################################################
######## sys stuff #############
###################################################################


##################################################################
C:\Users\cash_\Documents\Perl\02 Learn 21 Days ==>> perl -v

This is perl 5, version 26, subversion 1 (v5.26.1) built for MSWin32-x64-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2017, Larry Wall

Binary build 2601 404865 provided by ActiveState http://www.ActiveState.com
Built Dec 11 2017 12:23:25

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

omplete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl". If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.



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