cat file.txt | sed -r 's/([0-9]+)/,/g'
{02, 12, 04, 01, 07, 10, 11, 06, 08, 05, 03, 15, 13, 00, 14, 09,},
{14, 11, 02, 12, 04, 07, 13, 01, 05, 00, 15, 10, 03, 09, 08, 06,},
{04, 02, 01, 11, 10, 13, 07, 08, 15, 09, 12, 05, 06, 03, 00, 14,},
{11, 08, 12, 07, 01, 14, 02, 13, 06, 15, 00, 09, 10, 04, 05, 03,}
Explicação:
First capturing group ([0-9]+)
Match a single character (i.e. number) present in the table [0-9]+
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
0-9 a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
In other words, the [0-9]+ pattern matches an integer number (without decimals) even Inside longer strings, even words.
is called a "back reference" or "special escapes" in the sed documentation. It refers to the corresponding matching sub-expressions in the regexp. In other words, in this example, it inserts the contents of each captured number in the table followed by comma.