use Data::Dump qw(dump);
print dump( pack("c*", 10, 3, 30, 21 ) );   # outputs: "\n\3\36\25"
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Okay, that "\n" isn't octal notation obviously, it's the Perl string escape code.

Thank you, but I'm still missing a clue. The reason I remain confused is perlop:

The following escape sequences are available in constructs that interpolate, and in transliterations:

    Sequence Note Description
    \t tab (HT, TAB)
    \n newline (NL)
    \r return (CR)
    \f form feed (FF)
    \b backspace (BS)
    \a alarm (bell) (BEL)
    \e escape (ESC)
    \x{263A} 1,8 hex char (example: SMILEY)
    \x1b 2,8 restricted range hex char (example: ESC)
    \N{name} 3 named Unicode character or character sequence
    \N{U+263D} 4,8 Unicode character (example: FIRST QUARTER MOON)
    \c[ 5 control char (example: chr(27))
    \o{23072} 6,8 octal char (example: SMILEY)
    \033 7,8 restricted range octal char (example: ESC)

Should this not be "\n\003\036\025"?

Well footnote 7 does say:

Some contexts allow 2 or even 1 digit, but any usage without exactly three digits, the first being a zero, may give unintended results. (For example, in a regular expression it may be confused with a backreference; see "Octal escapes" in perlrebackslash.)

So it would be much more clear with the 3 digit representation. But in this particular context, it works out:

use feature 'say';
use Data::Dump qw(dump);
say dump( pack("c*", 10, 3, 30, 21 ) ); # outputs "\n\3\36\25"
say dump( unpack("c*", "\n\3\36\25") );  # outputs (10, 3, 30, 21)
say dump( unpack("c*", "\n\003\036\025") );  # outputs (10, 3, 30, 21)
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$ perl -le " print 041 "
33

$ perl -le " print chr 041 "
!

$ perl -le " print chr 33  "
!

$ perl -le " print ord q{!}  "
33
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So the integer 33 is written in octal as 041, and if you chr 33 you get !

Make sense?

In a double quoted string 041 is 041, but \041 is chr 33 (octal escape)

$ perl -le " print qq{041}  "
041

$ perl -le " print qq{\041}  "
!
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