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Asked: 2017-12-31 00:01:38 +0800 CST

sed /RegEx/,~N format address

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$ sed '/b/,~8 d' a-i.txt

I know what it does. But, they say "a multiple of 8" for ~8. Why is it expressed as "a multiple of 8"?

sed

1 Answers

  1. Best Answer

    /b/,~8 matches lines starting with a line containing b and continuing until a line is reached whose line number is a multiple of 8

    From man sed:

    addr1,~N
    Will match addr1 and the lines following addr1 until the next line whose input line number is a multiple of N.

    Examples

    This prints any line which contains 5 and all following lines up to and including the next line whose line number is a multiple of 8:

    $ seq 14 | sed -n '/5/,~8 p'
5
6
7
8

    This prints from a line containing 14 to the next line whose line number is a multiple of 8:

    $ seq 22 | sed -n '/14/,~8 p'
14
15
16

    This deletes all lines starting with a line matches 5 and ending with the next line whose line number is a multiple of 8:

    $ seq 10 | sed '/5/,~8 d'
1
2
3
4
9
10

    Similar but different

    This prints the fourth line and every eigtht line thereafter:

    $ seq 22 | sed -n '4~8 p'
4
12
20

    This prints a line matching 4 and the next three lines which follow:

    $ seq 13 | sed -n '/4/,+3 p'
4
5
6
7
    • 5