Perl Cookbook

Printing a List with Commas

Problem

You’d like to print out a list with an unknown number of elements with an “and” before the last element, and with commas between each element if there are more than two.

Solution

Use this function, which returns the formatted string:

sub commify_series {
    (@_ == 0) ? ''                                      :
    (@_ == 1) ? $_[0]                                   :
    (@_ == 2) ? join(" and ", @_)                       :
                join(", ", @_[0 .. ($#_-1)], "and $_[-1]");
}

Discussion

It often looks odd to print out arrays:

@array = ("red", "yellow", "green");
print "I have ", @array, " marbles.\n";
print "I have @array marbles.\n";

                  I have redyellowgreen marbles.
               
                  I have red yellow green marbles.

What you really want it to say is, "I have red, yellow, and green marbles". The function given in the solution generates strings in that format. The word "and" is placed between the last two list elements. If there are more than two elements in the list, a comma is placed between every element.

Example 4.1 gives a complete demonstration of the function, with one addition: If any element in the list already contains a comma, a semi-colon is used for the separator character instead.

Example 4-1. commify_series

#!/usr/bin/perl -w # commify_series - show proper comma insertion in list output @lists = ( [ 'just one thing' ], [ qw(Mutt Jeff) ], [ qw(Peter Paul Mary) ], [ 'To our parents', 'Mother Theresa', 'God' ], [ 'pastrami', 'ham and cheese', 'peanut butter and jelly', 'tuna' ], [ 'recycle tired, old phrases', 'ponder big, happy thoughts' ], [ 'recycle tired, old ...