linux awk删除文本重复行需要注意强制类型转换的问题

# cat 1.txt
2.1.10.1
2.1.10.2
2.11.0.1
2.11.0.2

# awk 'BEGIN{FS=OFS="."}{if(!a[$1.$2.$3]++)print}' 1.txt
2.1.10.1

# awk -F '.' '{a[$1.$2.$3]++;}END{for(i in a)print i"  "a[i]}' 1.txt
2110  4

# awk 'BEGIN{FS=OFS="."}{if(!a[$1"."$2"."$3]++)print}' 1.txt
2.1.10.1
2.11.0.1

# awk -F '.' '{a[$1"."$2"."$3]++;}END{for(i in a)print i"  "a[i]}' 1.txt
2.11.0  2
2.1.10  2