[20170705]diff比较执行结果的内容.txt

--//有时候需要比较2个命令输出的结果进行比较,比较笨的方法如下,例子:

$  lsnrctl status listener_scan2 > /tmp/b2.txt
$  lsnrctl status listener_scan3 > /tmp/b3.txt
$  diff -nur /tmp/b2.txt /tmp/b3.txt

--//很明显这样要生成2个文件,然后比较,实际上利用shell可以很简单的实现.

$  lsnrctl status listener_scan3 | diff /tmp/2.txt -
--//这样减少1个文件的生成,可以再减少文件生成吗?

$  diff
--//如何理解呢?
$  echo  /dev/fd/63 /dev/fd/62
--//实际上62,63就是打开的文件句柄.当然执行完马上关闭.

$  ls -l /dev/fd
lrwxrwxrwx 1 root root 13 2014-12-11 02:24:57 /dev/fd -> /proc/self/fd

$  ls -l /dev/fd/
total 0
lrwx------ 1 grid oinstall 64 2017-07-05 16:16:07 0 -> /dev/pts/4
lrwx------ 1 grid oinstall 64 2017-07-05 16:16:07 1 -> /dev/pts/4
lrwx------ 1 grid oinstall 64 2017-07-05 16:16:07 2 -> /dev/pts/4
lr-x------ 1 grid oinstall 64 2017-07-05 16:16:07 3 -> /proc/101318/fd

--//写一个简单的shell脚本就很好理解了(注意这种写法不是很严谨):
--//我直接读取句柄63,62的内容.

$  cat a.sh
#! /bin/bash
echo  diff /dev/fd/63 /dev/fd/62

$  . a.sh
/dev/fd/63 /dev/fd/62
6c6
---
> connecting to (description=(address=(protocol=ipc)(key=listener_scan3)))
9c9
---
> alias                     listener_scan3
11,12c11,12
---
> start date                30-jun-2017 12:00:58
> uptime                    5 days 4 hr. 17 min. 43 sec
17c17
---
> listener log file         /u01/app/11.2.0.4/grid/network/log/listener_scan3.log
19,20c19,20
---
>   (description=(address=(protocol=ipc)(key=listener_scan3)))
>   (description=(address=(protocol=tcp)(host=192.168.100.107)(port=1521)))

--//想到这里,我终于理解exp/imp on the fly.例子:

$ exp scott/book file=>(gzip >t.dmp.gz) tables=emp
$ imp scott/book full=y  file=