gawk中的“字符串数字(STRNUM)”

几天前在论坛看到一个帖子  这是个挺有意思的问题。
我自己做了几个试验，发现00e1有这个问题，但是00a1、00b1、00c1等其它字符串却没有这个问题。

前天，怀着忐忑的心情给 [e-mail] 发了一封邮件：

[bug report] gawk doesn’t work correctly when assign special value to variable
To: [e-mail]

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

[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" '$2==""var' 1.txt
gawk -v var="^00e1$" '$2~var' 1.txt

没想到，昨天就收到了来自 Andrew J. Schorr 大神的回复，效率还真是高呢，32个赞：

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":

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

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

看完那篇文档，似有所悟。但是还是没搞清楚为啥00a1、00b1、00c1等字符串没问题呢？
喝完一杯咖啡之后，恍然大悟：科学计数法！泥煤的~~~