为什么变量替换在这种awk单行代码中起作用？

Question

The Internet says that to use a shell variable in Awk, you can either double-quote the Awk program (which is a bad idea), or use Awk's variable-passing mechanism (which is the correct approach).

Why then do I get this?

$ export name=Andrew
$ echo 'hello' | awk '{system("echo ${name}, " $1)}'
Andrew, hello

Is it because Awk spawns a shell to execute the system command, the variable substitution is interpreted by that shell rather than by Awk, and that shell, being a sub-shell of the shell that launched Awk, inherits its shell variables?

Answer 1

awk passes the literal string echo ${name}, hello to the system shell to process. Because you exported name prior to calling awk , name=Andrew appears in awk 's environment, and awk passes it on to the system shell in turn. The shell then is able to expand ${name} to Andrew as a result.