Hack 11. Join Command

jion 命令用来combine连个文件，前提是这两个文件有共同的key，或者说有共同的域。如果两个文件域按顺序有不同的话，就会忽略不同的域，而只去combine相同顺序下的有共同field的行。

例如：　我现在有两个文件，一个是：ｅｍｐｌｏｙｅｅ．ｔｘｔ，另一个是ｂｏｎｕｘ．ｔｘｔ，彼此行记录一一对应〉

[[e-mail]1 hack101]$ cat employee.txt
100 Jason Smith
200 John Doe
300 Sanjay Gupta
400 Ashok Sharma
[[e-mail]1 hack101]$ cat bonus.txt
100 $5,000
200 $500
300 $3,000
400 $1,250
[[e-mail]1 hack101]$ jion employee.txt bonus.txt
-bash: jion: command not found
[[e-mail]1 hack101]$ join employee.txt bonus.txt
100 Jason Smith $5,000
200 John Doe $500
300 Sanjay Gupta $3,000
400 Ashok Sharma $1,250

如果ｂｏｎｕｘ．ｔｘｔ文件中间少了一个记录，那么该行记录就不会被ｃｏｍｂｉｎｅ。

[[e-mail]1 hack101]$ cat bonus.txt
100 $5,000
200 $500
400 $1,250
[[e-mail]1 hack101]$ join employee.txt bonus.txt
100 Jason Smith $5,000
200 John Doe $500
400 Ashok Sharma $1,250

如果ｂｏｎｕｓ．ｔｘｔ文件中间多了一行记录，虽然该记录无法匹配，但后面的记录可以匹配〉

[[e-mail]1 hack101]$ cat bonus.txt
100 $5,000
200 $500
201 $201
300 $oo
400 $1,250
[[e-mail]1 hack101]$ join employee.txt bonus.txt
100 Jason Smith $5,000
200 John Doe $500
300 Sanjay Gupta $oo
400 Ashok Sharma $1,250

经过测试得知：只要被修改的记录是按共同域的合理顺序来排序的，那么ｌｉｎｕｘ就可以做到正常的排序，　如下：

[[e-mail]1 hack101]$ cat bonus.txt
100 $5,000
200 $500
201 $201
202 $333
300 $oo
400 $222
401 $1,250
[[e-mail]1 hack101]$ join employee.txt bonus.txt
100 Jason Smith $5,000
200 John Doe $500
300 Sanjay Gupta $oo
400 Ashok Sharma $222

但是如果顺序不合理的话，ｌｉｎｕｘ就不会按正确的顺序来匹配〉
例如：

[[e-mail]1 hack101]$ cat bonus.txt
100 $5,000
200 $500
301 $201
302 $333
300 $oo
400 $222
401 $1,250
[[e-mail]1 hack101]$ join employee.txt bonus.txt
100 Jason Smith $5,000
200 John Doe $500
join: file 2 is not in sorted order
400 Ashok Sharma $222

--EOF--