Subject: cut runs wrong

From: zsw <[email-masked]>
Date: Wed, 5 Aug 2015 10:46:07 +0800 (CST)

I 'm a user of linux   today  I  find the  command    "cut"  runs wrong  , file 123 is :

1 2 3
4 5 6
7 8 9

after use the cut command :

$ cut -f1 123.txt
1 2 3
4 5 6
7 8 9

I  want to know where is wrong ,can you help me? thank you .