Formats in PERL, Practical Extraction and Report Language @ DomainAvenue.com | Domain Name Registration and Web Hosting on IBM/Hewlett-Packard (HP) Compaq Servers running Red Hat Linux 7.x w/Apache

Formats in PERL

Output record formats for use with the write-operator may declared as follows:

   format NAME =
   FORMLIST
   .

If name is omitted, format STDOUT is defined. FORMLIST consists of a sequence of lines, each of which may be of one of three types:

A comment.
A "picture" line giving the format for one output line.
An argument line supplying values to plug into a picture line.

Picture lines are printed exactly as they look, except for certain fields that substitute values into the line. Each picture field starts with either @ or ^. The @ field (not to be confused with the array marker @) is the normal case; ^ fields are used to do rudimentary multi-line text block filling. The length of the field is supplied by padding out the field with multiple <, >, or | characters to specify, respectively, left justification, right justification, or centering. As an alternate form of right justification, you may also use # characters (with an optional .) to specify a numeric field. (Use of ^ instead of @ causes the field to be blanked if undefined.) If any of the values supplied for these fields contains a newline, only the text up to the newline is printed. The special field @* can be used for printing multi-line values. It should appear by itself on a line.

The values are specified on the following line, in the same order as the picture fields. The values should be separated by commas.

Picture fields that begin with ^ rather than @ are treated specially. The value supplied must be a scalar variable name which contains a text string. Perl puts as much text as it can into the field, and then chops off the front of the string so that the next time the variable is referenced, more of the text can be printed. Normally you would use a sequence of fields in a vertical stack to print out a block of text. If you like, you can end the final field with ..., which will appear in the output if the text was too long to appear in its entirety. You can change which characters are legal to break on by changing the variable $: to a list of the desired characters.

Since use of ^ fields can produce variable length records if the text to be formatted is short, you can suppress blank lines by putting the tilde (~) character anywhere in the line. (Normally you should put it in the front if possible, for visibility.) The tilde will be translated to a space upon output. If you put a second tilde contiguous to the first, the line will be repeated until all the fields on the line are exhausted. (If you use a field of the @ variety, the expression you supply had better not give the same value every time forever!) For example,

 # a report on the /etc/passwd file
 format STDOUT_TOP =
                         Passwd File
 Name                Login    Office   Uid   Gid Home
 ------------------------------------------------------------
 .
 format STDOUT =
 @<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<
 $name,              $login,  $office,$uid,$gid, $home
 .
 
 # a report from a bug report form
 format STDOUT_TOP =
                         Bug Reports
 @<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>
 $system,                      $%,         $date
 ------------------------------------------------------------
 .
 format STDOUT =
 Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
          $subject
 Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<
        $index,                       $description
 Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<
           $priority,        $date,   $description
 From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<
       $from,                         $description
 Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<
              $programmer,            $description
 ~                                    ^<<<<<<<<<<<<<<<<<<<<<<
                                      $description
 ~                                    ^<<<<<<<<<<<<<<<<<<<<<<
                                      $description
 ~                                    ^<<<<<<<<<<<<<<<<<<<<<<
                                      $description
 ~                                    ^<<<<<<<<<<<<<<<<<<<<<<
                                      $description
 ~                                    ^<<<<<<<<<<<<<<<<<< ...
                                      $description
 .

It is possible to intermix prints with writes on the same output channel, but you'll have to handle $- (lines left on the page) yourself.

If you are printing lots of fields that are usually blank, you should consider using the reset operator between records. Not only is it more efficient, but it can prevent the bug of adding another field and forgetting to zero it.

Click here to go back to the Perl index