linux输入输出重定向使用详解

2019-10-14 16:04:14王振洲

               dbms_rowid.rowid_row_number('AAAZdQAAGAAATxjAAk') row# from dual
/


tee命令相当于把stdout副本写入文件,再把stdout传给下一个命令,但是错误内容是无法用tee传递的,如同使用>>追加内容,tee可以使用-a选项追加:

[~]$cat edit.sql /root/test.sh | tee -a temp.sh | cat -n
cat: /root/test.sh: Permission denied
select           dbms_rowid.rowid_object('AAAZdQAAGAAATxjAAk') data_object_id#,
             dbms_rowid.rowid_relative_fno('AAAZdQAAGAAATxjAAk') rfile#,
            dbms_rowid.rowid_block_number('AAAZdQAAGAAATxjAAk') block#,
               dbms_rowid.rowid_row_number('AAAZdQAAGAAATxjAAk') row# from dual
/
[~]$cat temp.sh
select           dbms_rowid.rowid_object('AAAZdQAAGAAATxjAAk') data_object_id#,
dbms_rowid.rowid_relative_fno('AAAZdQAAGAAATxjAAk') rfile#,
dbms_rowid.rowid_block_number('AAAZdQAAGAAATxjAAk') block#,
dbms_rowid.rowid_row_number('AAAZdQAAGAAATxjAAk') row# from dual
/
select           dbms_rowid.rowid_object('AAAZdQAAGAAATxjAAk') data_object_id#,
dbms_rowid.rowid_relative_fno('AAAZdQAAGAAATxjAAk') rfile#,
dbms_rowid.rowid_block_number('AAAZdQAAGAAATxjAAk') block#,
dbms_rowid.rowid_row_number('AAAZdQAAGAAATxjAAk') row# from dual
/

2.输入重定向:

输入重定向,在一些场合,例如数据库监控中用的比较多,常见的是使用内联重定向

[~]$cat < edit.sql
select           dbms_rowid.rowid_object('AAAZdQAAGAAATxjAAk') data_object_id#,
dbms_rowid.rowid_relative_fno('AAAZdQAAGAAATxjAAk') rfile#,
dbms_rowid.rowid_block_number('AAAZdQAAGAAATxjAAk') block#,
dbms_rowid.rowid_row_number('AAAZdQAAGAAATxjAAk') row# from dual
/

例如,如下操作,把 <<EOF > temp.sh到最后EOF之间的内容当作stdin,然后把stdout写入文件temp.sh

[~]$cat <<EOF > temp.s
this is my log
EOF
[~]$cat temp.sh
this is my log

3.自定义文件描述符:

自定义文件描述符的原理是使用基本的三种文件打开模式
只读(<)
截断(>)
追加(>>)
创建一个文件描述符3,用于打开文件
[~]# exec 3< test.sh
下面就可以直接使用文件描述符打开文件了,但是只能使用一次:

[~]# cat <&3
hello
hello

创建文件描述符4,用于写入文件(可以复用):

[~]# exec 4>test.sh
[~]# echo okok >&4
[~]# cat test.sh
okok