match(s, r [, a])

Return the position in s where the regular expression r occurs, or 0 if r is not present, and set the values of RSTART and RLENGTH. Note that the argument order is the same as for the ~ operator: str ~ re. If array a is provided, a is cleared and then elements 1 through n are filled with the portions of s that match the corre‐sponding parenthesized subexpression in r. The 0'th element of a contains the portion of s matched by the entire regular expression r. Subscripts a[n, "start"], and a[n, "length"] provide the starting index in the string and length respectively, of each matching substring.

1. Return the position in s where the regular expression r occurs, or 0 if r is not present

　　如果匹配到，match函數返回第一個字符的position；如果沒有匹配到，match函數返回0。

2. set the values of RSTART and RLENGTH

　　RSTART：若匹配到，則該值為 match函數 所匹配到的字符串的 開始位置；否則 該值為0。
　　RLENGHT：若匹配到，則該值為 match函數 所匹配到的字符串的 總長度；否則 該值為-1。

tmp.txt的內容
frank@ubuntu:~/test/tmp$ cat tmp.txt

1. RSTART 和 RLENGTH的含義

frank@ubuntu:~/test/tmp$ awk '{if(match($0,/^[.+]$/)){print $0, RSTART, RLENGTH}}' tmp.txt
[Frank] 1 7
[Mike] 1 6

這句命令的作用是：匹配以"["開頭和以"]" 結尾的內容。
RSTART：若匹配到，則該值為 match函數 所匹配到的字符串的 開始位置；否則 該值為0。
RLENGHT：若匹配到，則該值為 match函數 所匹配到的字符串的 總長度；否則 該值為-1。

2. match函數的返回值

frank@ubuntu:~/test/tmp$ awk -vr=0 '{r=match($0,/^[.+]$/); print $0, RSTART, RLENGTH, r}' tmp.txt
[Frank] 1 7 1
id=123 0 -1 0
age=18 0 -1 0
0 -1 0
[Mike] 1 6 1
id=456 0 -1 0
age=18 0 -1 0

Return the position in s where the regular expression r occurs, or 0 if r is not present
如果匹配到，match函數返回第一個字符的position；如果沒有匹配到，match函數返回0

　　3. ~ operator

正則匹配運算符
frank@ubuntu:~/test/tmp$ awk -vr=0 '{if($0~/^[.+]$/){print $0}}' tmp.txt
[Frank]
[Mike]

4. match 有第三個參數的情況

frank@ubuntu:~/test/tmp$ awk -vr=0 '{r=match($0,/^[.+]$/,a);{print $0, RSTART, RLENGTH, r, a[0]}}' tmp.txt
[Frank] 1 7 1 [Frank]
id=123 0 -1 0
age=18 0 -1 0
0 -1 0
[Mike] 1 6 1 [Mike]
id=456 0 -1 0
age=18 0 -1 0

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