choosing even-numbered rows from a file

How do I choose even numbered rows o开发者_JAVA百科f a file? I wish to select rows #2, 4, 6, etc. from a file that contains data. Can anyone help me with this?

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sed -n 'n;p' filename

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An awk example (as an alternative to Mark's sed example):

awk 'NR % 2 == 0' filename

Example:

$ cat filename
line 0
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8

$ awk 'NR % 2 == 0' filename
line 1
line 3
line 5
line 7

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With awk:

awk '{getline;print}' filename

With bash:

#!/bin/bash
while read line
do
    read line
    echo $line
done < filename

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If your sed is GNU's:

sed -n 2~2p filename