pack

Converts a list of values into a binary string according to a template.

Takes a TEMPLATE string and a LIST of values and packs them into a binary string. The template is a sequence of format characters, each optionally followed by a repeat count or * (consume all remaining).

Common format characters:

• a, A, Z – ASCII string (null-padded, space-padded, null-terminated)
• c, C – signed/unsigned char (8-bit)
• s, S – signed/unsigned short (16-bit native)
• l, L – signed/unsigned long (32-bit native)
• q, Q – signed/unsigned quad (64-bit native)
• n, N – unsigned short/long in network (big-endian) byte order
• v, V – unsigned short/long in VAX (little-endian) byte order
• f, d – single/double-precision float (native)
• H, h – hex string (high/low nybble first)
• w – BER compressed integer
• U – Unicode code point
• x – null byte padding
• X – back up one byte
• @ – null-pad to absolute position
• (...)N – group with repeat count

Whitespace and #-comments in templates are ignored.

Synopsis

my $bin = pack("A10", "hello");         # space-padded string
my $bin = pack("NnA*", $long, $short, $str);
my $bin = pack("(A2)*", @pairs);        # group repeat

Implementation Notes

perl5 reference: pp_pack.c:3175 PP_wrapped(pp_pack, 0, 1).

C structure: dSP; dMARK; dORIGMARK; dTARGET; SV *cat = TARG; // pad[op_targ] pat_sv = *++MARK; // template is first arg after mark MARK++; // advance past template SvPVCLEAR(cat); // clear cat, preserve UTF-8 off SvUTF8_off(cat); packlist(cat, pat, patend, MARK, SP + 1); SP = ORIGMARK; PUSHs(cat);

See Also

PP runtime: pack | unpack, vec