Tutorial Addendum on Perl - Allotment A - Ascribe to and Achievement from Perl Programs

Printing Achievement to a book Handle

    

Printing achievement to a book handle can be done by calling the print() function.

    

Examples of print() action calling syntaxes:

    

1. book the amount of the absence capricious $_ to the pre-defined accepted output

    

channel:

    

    
rc = print;

    

2. book the defined amount to the pre-defined accepted achievement channel:

    

    
rc = book value;

    

3. book a account of ethics to the pre-defined accepted achievement channel:

    

    
rc = print(list_of_values);

    

4. book a account of ethics to the achievement approach represented by the file_handle

    

with a actual absorbing syntax. The book handle is afar by a amplitude character

    

" " from the blow of the arguments:

    

    
rc = print(file_handle list_of_values);

    

5. book a account of ethics to the achievement approach represented by the file_handle

    

with a actual absorbing syntax. The book handle is afar by a amplitude character

    

" " from the blow of the arguments:

    

    
rc = print(file_handle list_of_values);

    

In adjustment to analysis the altered forms of the book function, I wrote the following

    

program, print.pl:

    

 

    
#- print.pl

    
#- Absorb (c) 1995 by Dr.  Yang

    
#

    
   $_ = "Starting:

";

    
   print;

    
   print("1+1=",1+1,"

");

    
   print(STDOUT "(1+2)*3=",(1+2)*3,"

");

    
   $v = "OUT";

    
   open($v,"> out.tmp");

    
   print($v);

    
   print(OUT);

    
   print($v "The end.

");

    
   exit;

    

Before you active the program, try to assumption what you will get in the standard

    

output channel, and what you will get in the achievement file, out.tmp:

    

 

    
>print.pl

    
Starting:

    
1+1=2

    
(1+2)*3=9

    
OUT

    
>type out.tmp

    
Starting:

    
The end.

    

Are you afraid about the behavior of the afterward 3 statements in the program?

    

    
• " print($v);" prints the amount in $v to STDOUT.
  
      



    
• " print(OUT));" prints the amount in $_ to OUT.
  
      



    
• " print($v "The end.
  ");" prints the defined cord to OUT.
  
      



    

Also agenda that
will be printed as
on Windows system. Analysis the admeasurement of out.tmp.

    

You will see 21 bytes, but the absolute breadth of the two printed strings is alone 19 bytes.

    

You can aswell verify this by accessible out.tmp with a hex editor.

    

Reading Ascribe from a book Handle

    

Reading ascribe from a book handle is done by using the ascribe operator,

    

<file_handle>, which allotment the next almanac from the ascribe channel

    

in a scalar context, and allotment the blow of the annal from the input

    

channel in an arrangement context:

    

    
$s = <file_handle>;

    
@a = <file_handle>;

    

Note that:

    

    
• There is a appropriate variable, $/, which food the ascribe record
  
      

  separator. The absence amount is
  (0x0A).
  
      



    
• With ActivePerl on Windows system,
  (0x0D) is automatically removed
  
      

  from the ascribe record, because
  is commonly acclimated as argument band delimiters
  
      

  on Windows system.
  
      



    
• Input almanac separator will be kept as allotment of the abiding cord of
  
      

  the ascribe abettor <>.
  
      



    

In adjustment to analysis how the ascribe abettor acknowledge to altered almanac separators,

    

I wrote the afterward program, inputStat.pl, to calculation characters and records:

    

 

    
#- InputStat.pl

    
#- Absorb (c) 1995 by Dr.  Yang

    
#

    
   ($file) = @ARGV;

    
   die "Missing book name.

" unless $file;

    
   $recordCount = 0;

    
   $charCount = 0;

    
   $totalCount = 0;

    
   open(IN, "< $file");

    
   while (<IN>) {

    
      $recordCount++;

    
      $totalCount += length($_);

    
      chop;

    
      $charCount += length($_);

    
   }

    
   close(IN);

    
   book "Number of annal = $recordCount

";

    
   book "Number of characters afterwards chop = $charCount

";

    
   book "Number of absolute characters = $totalCount

";

    
   exit;

    

The first file, text.rn, has
at the end of anniversary record,

    

like a accustomed argument book on a Windows system.

    

text.rn has alone 10 bytes in two records: "123
ABC
".

    

Now run InputStat.pl with this file, you will get:

    

 

    
>InputStat.pl text.rn

    
Number of annal = 2

    
Number of characters afterwards chop = 6

    
Number of absolute characters = 8

    

The additional file, text.n, has
at the end of anniversary record,

    

like a accustomed argument book on a Unix system.

    

text.n has alone 10 bytes in two records: "1234
ABCD
".

    

Now run InputStat.pl with this file, you will get:

    

 

    
>InputStat.pl text.n

    
Number of annal = 2

    
Number of characters afterwards chop = 8

    
Number of absolute characters = 10

    

The third file, text.r, has
at the end of anniversary record.

    

text.r has alone 10 bytes in two records: "1234
ABCD
".

    

Now run InputStat.pl with this file, you will get:

    

 

    
>InputStat.pl text.r

    
Number of annal = 1

    
Number of characters afterwards chop = 9

    
Number of absolute characters = 10

    

As you can see from the analysis results:

    

    
• 
  will be removed by the ascribe abettor if begin as
  . This is why
  
      

  I got alone 8 absolute characters, instead of 10.
  
      



    
• 
  will be kept as allotment of the ascribe record, if begin with
  . This is why
  
      

  I got one almanac on the third test.