2 Suggestions by pgy.
source | link

bash - 2929 27 characters

sort|uniq -c|sort -n|tailnr|sed -n1q

Using it:

sort|uniq -c|sort -n|tailnr|sed -n1q
4
3
1
0
6
1
6
4
4
0
3
1
7
7
3
4
1
1
2
8
[ctrl-D]
5 1

i.e. "1" is the mode, and it appears five times.

bash - 29 characters

sort|uniq -c|sort -n|tail -n1

Using it:

sort|uniq -c|sort -n|tail -n1
4
3
1
0
6
1
6
4
4
0
3
1
7
7
3
4
1
1
2
8
[ctrl-D]
5 1

i.e. "1" is the mode, and it appears five times.

bash - 29 27 characters

sort|uniq -c|sort -nr|sed q

Using it:

sort|uniq -c|sort -nr|sed q
4
3
1
0
6
1
6
4
4
0
3
1
7
7
3
4
1
1
2
8
[ctrl-D]
5 1

i.e. "1" is the mode, and it appears five times.

1
source | link

bash - 29 characters

sort|uniq -c|sort -n|tail -n1

Using it:

sort|uniq -c|sort -n|tail -n1
4
3
1
0
6
1
6
4
4
0
3
1
7
7
3
4
1
1
2
8
[ctrl-D]
5 1

i.e. "1" is the mode, and it appears five times.