linux系统中实现文件指定列的互换

[root@centos79 test3]# cat a.txt
3 5 6 2
s g 3 5
c f h e

[root@centos79 test3]# cat a.txt
3 5 6 2
s g 3 5
c f h e
[root@centos79 test3]# awk ‘{tmp = $1; $1 = $3; $3 = tmp; print $0}‘ a.txt
6 5 3 2
3 g s 5
h f c e