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11.4 More About the FieldholdersSo far, by example, you know that the fieldholder 11.4.1 Text FieldsMost fieldholders start with If the characters following the If the characters following the Finally, if the characters following the 11.4.2 Numeric FieldsAnother kind of fieldholder is a fixed-precision numeric field, useful for those big financial reports. This field also begins with format MONEY = Assets: @#####.## Liabilities: @#####.## Net: @#####.## $assets, $liabilities, $assets-$liabilities . The three numeric fields allow for six places to the left of the decimal place, and two to the right (useful for dollars and cents). Note the use of an expression in the format - perfectly legal and frequently used. Perl provides nothing fancier than this; you can't get floating currency symbols or brackets around negative values or anything interesting. To do so, you have to write your own spiffy subroutine, like so: format MONEY = Assets: @<<<<<<<<< Liabilities @<<<<<<<< Net: @<<<<<<<<< pretty($assets,10), pretty($liab,9), pretty($assets-$liab,10) . sub pretty { my($n,$width) = @_; $width -= 2; # back off for negative stuff $n = sprintf("%.2f",$n); # sprintf is in later chapter if ($n < 0) { return sprintf("[%$width.2f]", -$n); # negative numbers get brackets } else { return sprintf(" %$width.2f ", $n); # positive numbers get spaces instead } } ## body of program: $assets = 32125.12; $liab = 45212.15; write (MONEY); 11.4.3 Multiline FieldsAs mentioned earlier, Perl normally stops at the first newline of a value when placing the result into the output. One kind of fieldholder, the multiline fieldholder, allows you to include a value that may have many lines of information. This fieldholder is denoted by The substituted value will look just like the original text: four lines of value become four lines of output. For example: format STDOUT = Text Before. @* $long_string Text After. . $long_string = "Fred\nBarney\nBetty\nWilma\n"; write; generates the output: Text Before. Fred Barney Betty Wilma Text After. 11.4.4 Filled FieldsAnother kind of fieldholder is a filled field. This fieldholder allows you to create a filled paragraph, breaking the text into conveniently sized lines at word boundaries, wrapping the lines as needed. There are a few parts that work together here, but let's look at them separately. First, a filled field is denoted by replacing the
When Perl is filling the filled field, it takes the value of the variable and grabs as many words (using a reasonable definition of "word")[4] as will fit into the field. These words are actually ripped out of the variable - the value of the variable after filling this field is whatever is left over after removing the words. You'll see why in a minute.
So far, this isn't much different from how a normal text field works; we're printing only as much as will fit (except that we're respecting a word boundary rather than just cutting it off at the field width). The beauty of this filled field appears when you have multiple references to the same variable in the same format. Take a look at this: format PEOPLE = Name: @<<<<<<<<<<<<< Comment: ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $name, $comment ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment . Note that the variable What happens if the complete text occupies less than four lines? Well, you'll get a blank line or two. This result is probably OK if you are printing out labels and need exactly the same number of lines for each entry to match them up with the labels. But if you are printing out a report, many blank lines merely use up your printer's paper budget. To fix this, use the suppression indicator. Any line that contains a tilde ( format PEOPLE = Name: @<<<<<<<<<<<<< Comment: ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $name, $comment ~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment ~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment ~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment . Now, if the comment covers only two lines, the third and fourth lines are automatically suppressed. What if the comment is more than four lines? Well, we could make about 20 copies of the last two lines of that format, hoping that 20 lines will suffice. But that goes against the idea that Perl helps you to be lazy, so there's a lazy way to do it. Any line that contains two consecutive tildes will be repeated automatically until the result is a completely blank line. (The blank line is suppressed.) This changes our format to look like this: format PEOPLE = Name: @<<<<<<<<<<<<< Comment: ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $name, $comment ~~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<< $comment . This way, if the comment takes 1 line, 2 lines, or 20 lines, we are still OK. Note that the criterion for stopping the repeated line requires the line to be blank at some point. That means you probably don't want any constant text (other than blanks or tildes) on the line, or else the line will never become blank. |