printf zero padded string - perl

Question

The format of MAC addresses varies with the platform.
E.g. on HPUX I could get something like:
0:0:c:7:ac:1e
While Linux gives me
00:00:0c:07:ac:1e
I used to use awk in a kornshell script on CentOS5 to format this to 00000c07ac1e like shown below.
MAC="0:0:c:7:ac:1e"
echo $MAC | awk -F: '{printf( "%02s%02s%02s%02s%02s%02s\n", $1,$2,$3,$4,$5,$6)}'
Unfortunately our admin server now is Ubuntu 14LTS with a newer version of awk which doesn't support the zero padding in the %s format anymore and I get an undesired 0 0 c 7ac1e
So I now switched to perl and do:
echo $MAC | perl -ne '{#A=split(":"); printf( "%02s%02s%02s%02s%02s%02s", #A)}'
As this may break too in upcoming releases I am looking for a more robust but still compact way to format the string.

Answer 1

Your Perl snippet will not break in future releases. This is basic functionality. Changing it will break many, many programs. (Plus, Perl has a mechanism for introducing backwards incompatible changes without breaking existing program.)
Cleaned up:
echo "$MAC" | perl -ne'#F=split(/:/); printf("%02s%02s%02s%02s%02s%02s\n", #F)'
Shorter:
echo "$MAC" | perl -ne'printf "%02s%02s%02s%02s%02s%02s\n", split /:/'
Without the repetition:
echo "$MAC" | perl -ple'$_ = join ":", map sprintf("%02s", $_), split /:/'
There's -a if you want something more awkish:
echo "$MAC" | perl -F: -aple'$_ = join ":", map sprintf("%02s", $_), #F'

Answer 2

Bit long but should be pretty robust
awk -F: '{for(i=1;i<=NF;i++){while(length($i)<2)$i=0$i;printf "%s",$i;}print ""}'
How it works
1.Loop through fields
2.Whilst the field is less than 2 characters long add zeros to the front
3.print the field
4.print newline character at end.

Answer 3

If you were dealing with a number rather than hex, you could use %.Xd to indicate you want at least X digits.
$ awk -F: '{printf( "%.2d%.2d\n", $1, $2)}' <<< "0:23"
0023
^^
two digits
From The GNU Awk User’s Guide #5.5.3 Modifiers for printf Formats:
.prec
A period followed by an integer constant specifies the precision to
use when printing. The meaning of the precision varies by control
letter:
%d, %i, %o, %u, %x, %X
Minimum number of digits to print.
In this case, you need a more general approach to deal with each one of the blocks of the MAC address. You can loop through the elements and add a 0 in case their length is just 1:
awk -F: '{for (i=1;i<=NF;i++) #loop through the elements
{
if (length($i)==1) #if length is 1
printf("0") #add a 0
printf ("%s", $i) #print the rest
}
print "" #print a new line at the end
}' <<< "0:0:c:7:ac:1e"
This returns:
00000c07ac1e
^^ ^^ ^^
^^ ^^ ^^
Note awk '...' <<< "$MAC" is the same as echo "$MAC" | awk '...'.