1./etc/profile
用户登录时，自动读取/ect目录下profile文件，此文件包括
- 全局或局部环境变量
- PATH信息
- 终端设置
- 安全命令
- 日期信息或放弃操作信息
2.stty用法
stty用于设置终端特性。要查询现在的stty选项，使用stty -a
$stty -a
stty的一个选项为-g，此选项允许以只读格式保存stty现有设置，便于以后重置回stty.
3.显示变量
使用echo命令可以显示单个变量，并在变量名前加$，例如：
$ DOLLAR=99
$ echo ${DOLLAR}
99
$ LAST_FILE=s2
$ echo ${LAST_FILE}
s2
$ ERROR="This is user: $LOGNAME"
$ echo ${ERROR}
This is user: dongjichao
4.清除变量
使用unset命令清除变量
$ PC=enterprise
$ echo ${PC}
enterprise
$ unset PC
$ echo ${PC}
$
5.显示所有本地shell变量
$ set | more
6.测试变量是否已经设置
$ echo "The file is ${FILES:?}"
FILES: parameter null or not set
7.显示环境变量
$ CONSOLE=tty1; export CONSOLE
$ echo $CONSOLE
tty1
使用env命令可以查看所有的环境变量
$ env
8.使用export导出变量
有一父进程
$ cat father.sh
#!/bin/sh
echo "this is the father"
FILM="A Few Good Men"
echo "I like the file :$FILM"
#call the child script
export FILM #去掉此句，在child.sh中变量$FILM则为空
child.sh
echo "back to father"
echo "and the file is :$FILM"
子进程为
$ cat child.sh
#!/bin/sh
echo "called from father.. i am the child"
echo "film name is :$FILM"
FILM="Die Hard"
echo "changing file to :$FILM"
运行father输出：
$ father.sh
this is the father
I like the file :A Few Good Men
called from father.. i am the child
film name is :A Few Good Men
changing file to :Die Hard
back to father
and the file is :A Few Good Men
