Perl Cd Bookshelf [Electronic resources] نسخه متنی

2.16. Putting Commas in Numbers

2.16.1. Problem

You want to output a number with
commas in the right places. People like to see long numbers broken up
in this way, especially in reports.

2.16.2. Solution

Reverse the string so you can use backtracking to avoid substitution
in the fractional part of the number. Then use a regular expression
to find where you need commas, and substitute them in. Finally,
reverse the string back.

sub commify {
my $text = reverse $_[0];
$text =~ s/(\d\d\d)(?=\d)(?!\d*\.)/$1,/g;
return scalar reverse $text;
}

2.16.3. Discussion

It's a lot easier in regular
expressions to work from the front than from the back. With this in
mind, we reverse the string and make a minor change to the algorithm
that repeatedly inserts commas three digits from the end. When all
insertions are done, we reverse the final string and return it.
Because reverse is sensitive to its implicit
return context, we force it to scalar context.

This function can easily be adjusted to accommodate the use of
periods instead of commas, as are used in many countries.

Here's an
example of commify in action:

# more reasonable web counter :-)
use Math::TrulyRandom;
$hits = truly_random_value( );       # negative hits!
$output = "Your web page received $hits accesses last month.\n";
print commify($output);
Your web page received -1,740,525,205 accesses last month.

2.16.4. See Also

perllocale(1); the reverse
function in perlfunc(1) and Chapter 29 of
Programming Perl; the section "Adding Commas
to a Number with Lookaround" in Chapter 2 of Mastering
Regular Expressions, Second Edition