Print every n lines from a file

Question

I\'m trying to print every nth line from file, but n is not a constant but a variable.

For instance, I want to replace sed -n \'1~5p\'

Answer 1

You can do it like this for example:

i=3
sed "2,${i}s/.*/changed line/g" InputFile

Example:

AMD$ cat File
aaaaaaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbbbbbbbb
cccccccccccccccccccccc
ffffdffffdffffdffffdffffdffffdffffffffd
eeeeeeeeeeeeeeeeeeeeeeee
fffffffffffffffffffff
ggggggggggggggggggggg

AMD$ i=4; sed "2,${i}s/.*/changed line/g" File
aaaaaaaaaaaaaaaaaaaaaaaa
changed line
changed line
changed line
eeeeeeeeeeeeeeeeeeeeeeee
fffffffffffffffffffff
ggggggggggggggggggggg

The key is to use " " for variable substitution.