shell脚本问题，可能会用到grep,awk

Question

如下，有两个文件：
f1.txt
111 A
222 B
333 C

f2.txt
i have 111
he has 222
she has 333

想用shell实现最终输出为
f3.txt
i have 111
//A
he has 222
//B
she has 333
//C

Answer 1

awk '{if(ARGIND == 1) group[$1] = $2}{if(ARGIND > 1 && ($3 in group)) printf("%s // %s\n", $0,group[$3])}' 1 2