[20170705]diff比較執行結果的內容.txt

[20170705]diff比較執行結果的內容.txt

--//有時候需要比較2個命令輸出的結果進行比較,比較笨的方法如下,例子:

$  lsnrctl status LISTENER_SCAN2 > /tmp/b2.txt
$  lsnrctl status LISTENER_SCAN3 > /tmp/b3.txt
$  diff -Nur /tmp/b2.txt /tmp/b3.txt

--//很明顯這樣要生成2個文件,然後比較,實際上利用shell可以很簡單的實現.

$  lsnrctl status LISTENER_SCAN3 | diff /tmp/2.txt -
--//這樣減少1個文件的生成,可以再減少文件生成嗎?

$  diff <(lsnrctl status LISTENER_SCAN2) <(lsnrctl status LISTENER_SCAN3)

--//如何理解呢?
$  echo  <(lsnrctl status LISTENER_SCAN2) <(lsnrctl status LISTENER_SCAN3)
/dev/fd/63 /dev/fd/62
--//實際上62,63就是打開的文件句柄.當然執行完馬上關閉.

$  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

--//寫一個簡單的shell腳本就很好理解了(註意這種寫法不是很嚴謹):
--//我直接讀取句柄63,62的內容.

$  cat a.sh
#! /bin/bash
echo  <(lsnrctl status LISTENER_SCAN2) <(lsnrctl status LISTENER_SCAN3)
diff /dev/fd/63 /dev/fd/62

$  . a.sh
/dev/fd/63 /dev/fd/62
6c6
< Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN2)))
---
> Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN3)))
9c9
< Alias                     LISTENER_SCAN2
---
> Alias                     LISTENER_SCAN3
11,12c11,12
< Start Date                30-JUN-2017 12:00:03
< Uptime                    5 days 4 hr. 18 min. 37 sec
---
> 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_scan2.log
---
> Listener Log File         /u01/app/11.2.0.4/grid/network/log/listener_scan3.log
19,20c19,20
<   (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER_SCAN2)))
<   (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.100.109)(PORT=1521)))
---
>   (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER_SCAN3)))
>   (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=192.168.100.107)(PORT=1521)))

--//想到這裡,我終於理解exp/imp on the fly.例子:

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