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 Hall
 
 
 
 

  
  COLUMMNAR
 
 
 
 

  
  


 
 

  
  open 
  
  my 
  
  (
  
  $fh
  
  ), 
  
  '<'
  
  , 
  
  
  
  $string
  
  ;
 
 
 
 

  
  my 
  
  @headers 
  
  = 
  
  unpack 
  
  $format
  
  , 
  
  <$fh>
  
  ;
 
 
 
 

  
  my 
  
  @names
  
  ;
 
 
 
 

  
  while
  
  (
  
  <$fh>
  
  ) 
  
  {
 
 
 
 

  
  ????
  
  my 
  
  %hash
  
  ;
 
 
 
 

  
  ????
  
  @hash 
  
  { 
  
  @headers 
  
  } 
  
  = 
  
  $_
  
  ;
 
 
 
 

  
  ????
  
  push 
  
  @names
  
  ,128)">%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.