上周有遇到过这个问题 awk '{print $$1}' 这个$$是什么用法呢
间接字段寻址,其类似

awk '{print $$1}' ===> awk '{print $($1)}' ===> awk '{Nr=$1; print $Nr}'

示例:

$ echo -e "1 b c d\n2 b c d\n3 b c d\n4 b c d" 
1 b c d
2 b c d
3 b c d
4 b c d

$ echo -e "1 b c d\n2 b c d\n3 b c d\n4 b c d" | awk '{print $$1}'
1  # since filed #1=1 result print first field
b  # since filed #1=2 result print secondfield
c  # since filed #1=3 result print third field
d  # since filed #1=4 result print fourth field

类似$可以根据需要添加更多

awk '{print $$$1}' ===>  awk '{print $$($1)}' ===> awk '{print $($($1))}'