把一个文件的偶数行,或者奇数行提取出来

>>第一种方法<<

sed -n '1~2p'

sed -n '2~2p'

info sed `FIRST~STEP' This GNU extension matches every STEPth line starting with line FIRST. In particular, lines will be selected when there exists a non-negative N such that the current line-number equals FIRST + (N * STEP). Thus, to select the odd-numbered lines, one would use `1~2'

'FIRST~STEPp'
意为提取行是从FIRST处开始，每隔（步长）为STEP

>>第二种方法<<

awk 'NR%2==1' file
awk 'NR%2==0' file