regex - Delete lines from file with SED or AWK

Question

Ive seen many variations, very confused on how to solve these 3 problems.

1. deleting all rows except the first from a file
2. deleting a row from file with a line number
3. deleting rows from a file with a range of line numbers

Answer 1

Using sed:

Delete 1st line:

sed '1d' file-name

Delete 10th line:

sed '10d' file-name

Delete line # 5 to 10

sed '5,10d' file-name

All above sed commands will write output on stdout that you can redirect to another file if you want or use -i flag of sed to inline edit the file.