Two things need to note for unpack in Perl

概述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

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.

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