# cat sort.txt
1 2
2 2
3 2
1 1
1 2

# sort -k1 sort.txt

1 1
1 2
1 2
2 2
3 2
# sort -k1,2 sort.txt

1 1
1 2
1 2
2 2
3 2
# sort -u -k1,2 sort.txt

1 1
1 2
2 2
3 2
# sort -u -k1 sort.txt

1 1
1 2
2 2
3 2
#