开始学习AWK，请高手解释NR==FNR是什么意思？

lcz88990200

s2002408030068:527:527::/home/dz02/s2002408030068:/bin/pw
s2002408032819:528:528::/home/dz02/s2002408032819:/bin/pw
s2002408032823:529:529::/home/dz02/s2002408032823:/bin/pw

文件shadow:
s20024080300681$d8NwFclG$v4ZTacfR2nsbC8BnVd3dn1:12676:0:99999:7:::
s20024080328191$UAvNbHza$481Arvk1FmixCP6ZBDWHh0:12676:0:99999:7:::
s20024080328231$U2eJ3oO1$bG.eKO8Zupe0TnyFhWX9Y.:12676:0:99999:7:::

用shadow文件中的密文部分替换passwd中的"x",生一个新passwd文件,如下所示
s20024080300681$d8NwFclG$v4ZTacfR2nsbC8BnVd3dn1:527:527::/home/dz02/s2002408030068:/bin/pw
s20024080328191$UAvNbHza$481Arvk1FmixCP6ZBDWHh0:528:528::/home/dz02/s2002408032819:/bin/pw
s20024080328231$U2eJ3oO1$bG.eKO8Zupe0TnyFhWX9Y.:529:529::/home/dz02/s2002408032823:/bin/pw

awk 'BEGIN{OFS=FS=":"} NR==FNR{a[$1]=$2}NR>FNR{$2=a[$1];print}' shadow passwd

NR==FNR,第一个文件shadow，以$1为下标，将$2的值赋给数组a
NR>FNR，第二个文件passwd，将文件shadow$2的值赋值给文件passwd

请高手解释NR==FNR什么意思？

personball

回复 1# lcz88990200


    一般高手不屑讲这个的，浪费他们精力。。。
lz 自己去搜索一下awk的几个变量的定义就知道了

http://www.cnblogs.com/huangwei/archive/2010/07/28/1787269.html

yestreenstars

就是针对第一个文件进行处理