awk命令末尾数字的作用

1、测试数据

[root@centos7 test]# cat a.txt
1 2 3
4 5 6
7 8 9

2、 数字的作用相当于print？

[root@centos7 test]# cat a.txt
1 2 3
4 5 6
7 8 9
[root@centos7 test]# awk '{if(NR == 1) {$1 = "a"} else if(NR == 2) {$1 = "b"} else {$1 = "c"}}1' a.txt
a 2 3
b 5 6
c 8 9
[root@centos7 test]# awk '{if(NR == 1) {$1 = "a"} else if(NR == 2) {$1 = "b"} else {$1 = "c"}}' a.txt
[root@centos7 test]# awk '{if(NR == 1) {$1 = "a"} else if(NR == 2) {$1 = "b"} else {$1 = "c"} {print $0}}' a.txt
a 2 3
b 5 6
c 8 9

3、

[root@centos7 test]# cat a.txt
1 2 3
4 5 6
7 8 9
[root@centos7 test]# awk '{if(NR == 1) $1 = "a"; else if(NR ==2) $1 = "b"; else $1 = "c"}' a.txt
[root@centos7 test]# awk '{if(NR == 1) $1 = "a"; else if(NR ==2) $1 = "b"; else $1 = "c"}1' a.txt
a 2 3
b 5 6
c 8 9