RUBY: String formatting and conversion

"% 05d" % 123 the result is "00123"
"% 02x" % 10 returns "0a"
"% 03x" % 10 the result is "00a"
"% 010x" % 10 returns "000000000a" (9 prefixes 0)
"% 10x" % 10 returns "a" (with a prefix of 9 spaces)

We can see that the first digit is the prefix, followed by the length, and then the X table is in hexadecimal notation, and D indicates the 10th hexadecimal notation.

It can be regarded as an amazing trick, but Ruby is a wonderful trick. It is very useful and brings great efficiency to development and makes the language elegant and concise ~