awk 的怪異現象以及其解決之道：正則表達式範圍與語言環境的悲傷故事

[root@centos ~]# echo abcABC | /bin/gawk '{gsub(/([a-z])/, "x"); print $0}'
xxxxxx
[root@centos ~]# echo abcABC | /bin/gawk '{gsub(/([[:lower:]])/, "x"); print $0}' 
xxxABC

問題1：神奇了，[a-z]不能表示小寫了！ 咋回事兒呢？

[root@centos ~]# /bin/gawk 'BEGIN{match("womasdRDfadfasKNd",/[A-Z][A-Z]+/);print RSTART,RLENGTH}'
1 3

問題2：輸出怎麼是1 3，按道理不應該是7 2麼？

往下看：

[root@centos ~]# /bin/gawk --version
GNU Awk 3.1.5
Copyright (C) 1989, 1991-2005 Free Software Foundation.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
[root@centos ~]# 
[root@centos ~]# echo $LANG
en_US.UTF-8
[root@centos ~]# echo abcABC | /bin/gawk '{gsub(/[a-z]/,"x");print $0}'
xxxxxx
[root@centos ~]# export LANG=C 
[root@centos ~]# echo abcABC | /bin/gawk '{gsub(/[a-z]/,"x");print $0}'
xxxABC
[root@centos ~]# 
[root@centos ~]# 

以上是3.1.5版本的結果。

CU上經過了一番激烈的討論，終於發現了問題之所在，原來以上問題原來是awk的正則表達式與語言環境的一個悲傷的故事導致的，請閱讀：

http://www.gnu.org/software/gawk/manual/html_node/Ranges-and-Locales.html

這個英文文檔只看懂了個大概，裏邊兒說awk在4.0版本中已經解決了這個問題！於是我下載了新版本進行測試，果然OK了！

[root@centos ~]# /usr/local/bin/gawk --version
GNU Awk 4.1.0, API: 1.0
Copyright (C) 1989, 1991-2013 Free Software Foundation.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
[root@centos ~]# 
[root@centos ~]# echo $LANG
en_US.UTF-8
[root@centos ~]# 
[root@centos ~]# /usr/local/bin/gawk '{gsub(/[a-z]/,"x");print $0}'              

[root@centos ~]# echo abcABC | /usr/local/bin/gawk '{gsub(/[a-z]/,"x");print $0}'
xxxABC
[root@centos ~]# 
[root@centos ~]# 
[root@centos ~]# 

以上是4.1.0版本的，很顯然是正確的了！

參考：

1. http://bbs.chinaunix.net/thread-4065242-1-1.html

2. http://bbs.chinaunix.net/thread-4103721-1-1.html