gawk中的字符串數字(STRNUM)介紹

幾天前在論壇看到一個帖子 http://bbs.chinaunix.net/thread-4184581-1-1.html 這是個挺有意思的問題。
我自己做了幾個試驗，發現00e1有這個問題，但是00a1、00b1、00c1等其它字符串卻沒有這個問題。

前天，懷著忐忑的心情給 [email protected] 發了一封郵件：

[bug report] gawk doesn’t work correctly when assign special value to variable
To: [email protected]

1. Symptom:
gawk doesn’s work correctly when assign special value (like 00e1) variable.

2. Steps to repeat this issue:

1) Download and compile the latest gawk 4.1.3
http://ftp.gnu.org/gnu/gawk/
[root]# gawk --version | head -2
GNU Awk 4.1.3, API: 1.1
Copyright (C) 1989, 1991-2015 Free Software Foundation.

2) Prepare a test file
cat > 1.txt << EOF
00e1 00e1
00e2 00e4
00e3 00e1_01
EOF

3) Execute following command to see the result
[root]# gawk -v var="00e1" '$2==var' 1.txt
00e1 00e1
00e2 00e4

The second line should not be there. Because "00e4" is NOT equal to "00e1" obviously.
Is it a bug or by design?

3. Workaround:
gawk -v var="00e1" '$2==""var' 1.txt
gawk -v var="^00e1___FCKpd___0quot; '$2~var' 1.txt

沒想到，昨天就收到了來自 Andrew J. Schorr 大神的回復，效率還真是高呢，32個贊：

On Thu, Aug 06, 2015 at 03:55:50PM +0800, Shell_HAT wrote:
> The second line should not be there. Because "00e4" is NOT equal to "00e1" obviously.
> Is it a bug or by design?

This is a tricky area. Please check the manual for the discussion of "String Type versus Numeric Type":
http://www.gnu.org/software/gawk/manual/html_node/Variable-Typing.html

I think the command-line assignment results in a variable of type STRNUM.

> 3. Workaround:
> gawk -v var="00e1" '$2==""var' 1.txt
> gawk -v var="^00e1___FCKpd___1quot; '$2~var' 1.txt

These examples may also be helpful:

bash-4.2$ gawk 'BEGIN {var = "00e1"} $2 == var' 1.txt
00e1 00e1
bash-4.2$ gawk 'BEGIN {var = 00e1} $2 == var' 1.txt
00e1 00e1
00e2 00e4

Regards,
Andy

看完那篇文檔，似有所悟。但是還是沒搞清楚為啥00a1、00b1、00c1等字符串沒問題呢？
喝完一杯咖啡之後，恍然大悟：科學計數法！泥煤的~~~