详细解释AWK语法(NR,FNR,NF)

Question

我正在学习使用 awk 进行文件比较。

我发现语法如下，

awk '
(NR == FNR) { 
    s[$0]
    next 
} 
{ 
    for (i=1; i<=NF; i++) 
        if ($i in s) 
            delete s[$i] 
} 
END { 
    for (i in s) 
        print i 
}' tests tests2

我无法理解语法是什么......你能详细解释一下吗？

它到底有什么作用？

Answer 1

awk '                      # use awk
(NR == FNR) {              # process first file
    s[$0]                  # hash the whole record to array s
    next                   # process the next record of the first file
} 
{                          # process the second file
    for (i=1; i<=NF; i++)  # for each field in record
        if ($i in s)       # if field value found in the hash
            delete s[$i]   # delete the value from the hash
} 
END {                      # after processing both files 
    for (i in s)           # all leftover values in s
        print i            # are output
}' tests tests2

例如，对于文件：

tests:
1
2
3

tests2:
1 2
4 5

程序将输出：

3