$ perl -le 'printf( "%04x\n", 12)'
000c

##</code><code>##

perl -le 'printf( "\\x%02x\\x%02x\n", 12 )' # WRONG
\x0c\x00

##</code><code>##

perl -le 'printf( "\\x%02x\\x%02x\n", unpack( "C2", 12 ))' WRONG
\x31\x32

##</code><code>##

perl -le 'printf( "\\x%02x\\x%02x\n", unpack( "C2", pack("S", 12)))'
\x0c\x00

##</code><code>##

perl -le 'printf( "\\x%02x\\x%02x\n", unpack( "C2", pack("n", 12)))'
\x00\x0c
# Another way to say that . . .
perl -le 'printf( "\\x%02x\\x%02x\n", unpack( "C2", pack("S>", 12)))'
\x00\x0c