永久重定向

如果在脚本中重定向许多数据，那么重定向每个echo语句就不太方便了，这种情况下，可以使用exec命令通知shell脚本执行期间重定向特定的文件描述符

文件名为： sh12.sh 

#!/bin/bash
# redirecting all output to a file
exec 1>testout

echo "This is a test of redirecting all output"
echo "from a script to another file."
echo "without haviing to redirect every individual line"

exec命令启动一个新的shell，并将STDOUT文件描述重定向到一个文件，所有定向到STDOUT的脚本输出都将重定向到这个文件

运行 sh sh12.sh ,你会发现没输出任何东西，然后查看testout文件， cat testout 

输出：

This is a test of redirecting all output
from a script to another file.
without haviing to redirect every individual line

然后将错误信息和正确信息分别重定向不同的文件

文件名 sh13.sh 

#!/bin/bash
# redirecting output to different locations

exec 2>testerror

echo "This is the start of the script"
echo "now reidirecting all output to another location"

exec 1>testout

echo "This output should go to the testout testout file"
echo "but this should go to the testerror file" >&2

运行 sh sh13.sh 

输出：

This is the start of the script
now reidirecting all output to another location

查看testout文件的内容 cat testout 

输出： This output should go to the testout testout file 

查看testerror文件的内容 cat testrror 

输出： but this should go to the testerror file