in reply to Formatting with sprintf

The answers thus far do not really go into a why, so I will weigh in.

sprintf is intended to take individual values and insert them into a template. In this case, your values do not remain continuous, so that means before you use a sprintf you need to separate the 4 digits sequences before re-joining them. You can split a couple of different ways:

and you can join them together a couple different ways

You can also do it with a compound operation like (my $CCformatted = $cardNum) =~ s/.{4}\K(?=.)/-/g;. TIMTOWTDI. I think my $CCformatted = join '-', unpack '(A4)*', $cardNum; is cleanest, but YMMV.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

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Re^2: Formatting with sprintf
by AnomalousMonk (Archbishop) on Nov 10, 2015 at 16:01 UTC

    I think I also prefer the join/unpack approach, but here's a regex with the highly prized "one-liner" property that works at least back to 5.8.9: 

    c:\@Work\Perl>perl -wMstrict -le
"print qq{perl version $]};
 ;;
 for my $cc (qw(
   1234987656785432 0000000000000000 0001000200030004 1000200030004000
   )) {
   print qq{'$cc'};
   ;;
   (my $fcc = $cc) =~ s{ \B (?= (?: ....)+ \z) }{-}xmsg;
   print qq{'$fcc' \n};
   }
"
perl version 5.008009
'1234987656785432'
'1234-9876-5678-5432'

'0000000000000000'
'0000-0000-0000-0000'

'0001000200030004'
'0001-0002-0003-0004'

'1000200030004000'
'1000-2000-3000-4000'

    [download]

    Give a man a fish:  <%-{-{-{-<

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