[root@stu227 he]# touch he.txt
[root@stu227 he]# set -o noclobber
[root@stu227 he]# echo "123" > he.txt

bash: he.txt: cannot overwrite existing file

如果要取消限制，就把set -o 改为set +o

[root@stu227 he]# set +o noclobber
[root@stu227 he]# echo "123" > he.txt
[root@stu227 he]# cat he.txt
123

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