ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt 
abc
abcd
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 1
a
a
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 2
b
b
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 1-2
ab
ab
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 1-3
abc
abc
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 1-4
abc
abcd
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 1-5
abc
abcd
ubuntu@VM-0-15-ubuntu:~/taoge$ cat b.txt | cut -c 1-6
abc
abcd
ubuntu@VM-0-15-ubuntu:~/taoge$ 

echo 123:456:789 | cut -c3
3

echo 123:456:789 | cut -c3-6
3:45

echo 123:456:789 | cut -c-3
123

echo 123:456:789 | cut -c3-
3:456:789

echo 123:456:789 | cut -c3-6,8-10
3:45:78

echo 123:456:789 | cut -c1,3,5,7
1346

echo 123:456:789 | cut -d : -f 3
789

[xxx@~]$ cut --help

Usage: cut OPTION... [FILE]...
Print selected parts of lines from each FILE to standard output.

Mandatory arguments to long options are mandatory for short options too.
 -b, --bytes=LIST    select only these bytes
 -c, --characters=LIST  select only these characters
 -d, --delimiter=DELIM  use DELIM instead of TAB for field delimiter
 -f, --fields=LIST    select only these fields; also print any line
              that contains no delimiter character, unless
              the -s option is specified
 -n           (ignored)
   --complement    complement the set of selected bytes, characters
              or fields
 -s, --only-delimited  do not print lines not containing delimiters
   --output-delimiter=STRING use STRING as the output delimiter
              the default is to use the input delimiter
   --help   display this help and exit
   --version output version information and exit