awk打开多个文件的方法

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