Convert String to HEX using sed command - bash

Question

I need to convert a string in chinese to its appropriate HEX format. I can do it using sed in the following way
echo -n 欢迎 | xxd -p -u | sed 's/.\{2\}/&\\x/g' | sed 's/^\(.\{0\}\)/\1\\x/' | sed -r 's/(.*)\\x/\1 /'
which gives me output as:
\xE6\xAC\xA2\xE8\xBF\x8E
This is correct answer that I am looking for. Please suggest me making using of sed more efficiently in above command. The above command is being run on ubuntu 16.04 terminal

Answer 1

You can chain sed-commands with ";":
echo -n 欢迎 | xxd -p -u | sed 's/.\{2\}/&\\x/g;s/^\(.\{0\}\)/\1\\x/' | sed -r 's/(.*)\\x/\1 /'
\xE6\xAC\xA2\xE8\xBF\x8E
Since you use sed and sed -r interchangingly, you have to modify the second, remaining sed call, to combine the remaining ones:
echo -n 欢迎 | xxd -p -u | sed 's/.\{2\}/&\\x/g;s/^\(.\{0\}\)/\1\\x/;s/\(.*\)\\x/\1 /'
Having a second look at it, what the output of xxd is without sed, I observed, the solution is much more easy:
echo -n 欢迎 | xxd -p -u | sed -r 's/(..)/\\x\1/g'
Your initial approach appended \x to 2 characters, but you can preceed it your pairs. However chaining multiple sed commands might still be a useful thing to know.

Answer 2

From an efficiency standpoint, about the best option I could come up with would be to replace xdd, 3-pipes, and 3 calls to sed with od and 2 bash parameter expansions. (there may be more efficient ways, but this was what came to mind)
For example, you could assign the result of command substitution $(printf "欢迎" | od -A none -t x1) to a variable which would contain ' e6 ac a2 e8 bf 8e'. Then it is simply a matter of converting to upper-case and then using a substring replacement of 'space' to '\x' (both provided by bash parameter expansions, e.g.
a=$(printf "欢迎" | od -A none -t x1); \
a=${a^^}; \
a=${a// /\\x}; \
echo $a
\xE6\xAC\xA2\xE8\xBF\x8E
(shown with line-continuations above, you can just copy/paste into your terminal to test)
From Your Request in Comment for C
The code in C to output the upper-case hex bytes contained in your string is trivial, e.g.
#include <stdio.h>
int main (void) {
char *s = "欢迎";
while (*s) /* output each byte in upper-case hex */
printf ("\\x%hhX", ((unsigned char)*s++));
putchar ('\n');
return 0;
}
Example Use/Output
$ ./bin/str2hexbytes
\xE6\xAC\xA2\xE8\xBF\x8E
(note: you could use the exact-width types in stdint.h and the exact-width format specifiers provided in inttypes.h for a more formal solution, but it would accomplish the same thing. Similarly, you could use wide-character types, but virtually all modern compilers have no problem handling multibyte characters in an ordinary string or array of char)