Two things need to note for unpack in Perl

In item 116 of the book  "Effective Perl", author demonstrates how to use unpack to process fix-width columnar data.
I tried to write a toy code for practice,  and found two things need to note.

First thing,  MUST use  single quote '  before and after the format string,  or you'll get unexpected result,  because @xx can be parsed as an array in Perl if enclosed within double quote.

Second thing,  format @xxx makes unpack move to specified position, NOTICE here unpack will work from position xxx+1, not position xxx.

Code is as below.

my $format = 'A2 @4 A10 @16 A6 @24 A*';
my $string = <<'COLUMMNAR';ID  First Name  Middle  Last Name                      1  brian       d       foy 2  Joshua              McAdams  3  Joseph      N       HallCOLUMMNAR
open my ($fh), '<', \$string;my @headers = unpack $format, <$fh>;my @names;while(<$fh>) {    my %hash;    @hash { @headers } = unpack $format, $_;    push @names, \%hash;}
use Data::Dumper::Names;print Dumper( \@names );

• Update:  I should say above format  of unpack in Perl is very similar with REXX.  Moreover, REXX is older than Perl, so MAYBE Perl community learned the pattern from REXX.