1、当awk读取的文件只有两个的时候，比较常用的有三种方法
（1）awk ‘NR==FNR{...}NR>FNR{...}‘ file1 file2
（2）awk ‘NR==FNR{...}NR!=FNR{...}‘ file1 file2
（3）awk ‘NR==FNR{...;next}{...}‘ file1 file2
next表示下一个命令不被执行
2、当awk处理的文件超过两个时，显然上面那种方法就不适用了。因为读第3个文件或以上时，也满足NR>FNR (NR!=FNR)，显然无法区分开来。
所以就要用到更通用的方法了：
（1）ARGIND 当前被处理参数标志: awk ‘ARGIND==1{...}ARGIND==2{...}ARGIND==3{...}... ‘ file1 file2 file3 ...
（2）ARGV 命令行参数数组: awk ‘FILENAME==ARGV[1]{...}FILENAME==ARGV[2]{...}FILENAME==ARGV[3]{...}...‘ file1 file2 file3 ...
（3）把文件名直接加入判断: awk ‘FILENAME=="file1"{...}FILENAME=="file2"{...}FILENAME=="file3"{...}...‘ file1 file2 file3 ...
举例说明，这个例子在面试的时候问过。
a.txt中有一列：
A
B
C
D
E
b.txt中有两列：
A hello world
A good morning
B what
C sad
D interview someone
D feeling bad
E not so good
E want to be happy
F fail to pass the exam
G good result
则打印出b.txt中的行，满足b.txt中第一列等于a.txt的第一列。
#! /usr/bin/ksh
print "Method1:########"
awk ‘ARGIND==1{test[NR]=$1}
ARGIND==2{for(i in test){if(test[i]==$1){print $0}}}‘ a.txt b.txt
print "\nMethod2:########"
#the ‘{" must at the same line of the NR!=FNR
gawk ‘NR==FNR{test[NR]=$1}
NR!=FNR{
for( i in test)
{
if(test[i]==$1)
print $0
}
}‘ a.txt b.txt
print "\nMethod3:########"
gawk ‘NR==FNR{test[NR]=$1}
NR>FNR{
for( i in test)
{
if(test[i]==$1)
print $0
}
}‘ a.txt b.txt
print "\nMethod4:########"
gawk ‘NR==FNR{test[NR]=$1;next}
{
for( i in test)
{
if(test[i]==$1)
print $0
}
}‘ a.txt b.txt
print "\nMethod5:########"
gawk ‘FILENAME==ARGV[1]{test[NR]=$1}
FILENAME==ARGV[2]{
for( i in test)
{
if(test[i]==$1)
print $0
}
}‘ a.txt b.txt
print "\nMethod6:########"
gawk ‘FILENAME=="a.txt"{test[NR]=$1}
FILENAME=="b.txt"{
for( i in test)
{
if(test[i]==$1)
print $0
}
}‘ a.txt b.txt
输出结果为：
Method1:######## A hello world A good morning B what C sad D interview someone D feeling bad E not so good E want to be happy Method2:######## A hello world A good morning B what C sad D interview someone D feeling bad E not so good E want to be happy Method3:######## A hello world A good morning B what C sad D interview someone D feeling bad E not so good E want to be happy Method4:######## A hello world A good morning B what C sad D interview someone D feeling bad E not so good E want to be happy Method5:######## A hello world A good morning B what C sad D interview someone D feeling bad E not so good E want to be happy Method6:######## A hello world A good morning B what C sad D interview someone D feeling bad E not so good E want to be happy