1:全局环境变量
1.1:查看全局变量 printenv/env
yusuwudeMacBook-Pro:bin yusuwu$ printenv TERM_PROGRAM=Apple_Terminal TERM=xterm-256color SHELL=/bin/bash ... SHLVL=1 LOGNAME=yusuwu _=/usr/bin/printenv yusuwudeMacBook-Pro:bin yusuwu$
1.2:显示个别环境变量的值 printenv EnvironmentVariableName /echo $EnvironmentVariableName
yusuwudeMacBook-Pro:bin yusuwu$ printenv HOME /Users/yusuwu yusuwudeMacBook-Pro:bin yusuwu$ env HOME env: HOME: No such file or directory yusuwudeMacBook-Pro:bin yusuwu$ echo $HOME /Users/yusuwu yusuwudeMacBook-Pro:bin yusuwu$
1.3:全局变量在子shell中通用
yusuwudeMacBook-Pro:bin yusuwu$ bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ echo $HOME /Users/yusuwu bash-3.2$ exit exit yusuwudeMacBook-Pro:bin yusuwu$
2:局部环境变量
2.1查看局部变量
遗憾的是在linux系统中并没有一个只显示局部变量的命令,set命令会显示某个特定进程设置的所有环境变量,包括局部变量,全局变量以及用户自定义变量.
2.2:设置用户自定义变量
yusuwudeMacBook-Pro:bin yusuwu$ echo $lala yusuwudeMacBook-Pro:bin yusuwu$ lala=hello yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello yusuwudeMacBook-Pro:bin yusuwu$ lala=hello world -bash: world: command not found yusuwudeMacBook-Pro:bin yusuwu$ lala="hello world" yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello world yusuwudeMacBook-Pro:bin yusuwu$ lala= "hello ysw" -bash: hello ysw: command not found yusuwudeMacBook-Pro:bin yusuwu$ lala ="hello ysw" -bash: lala: command not found yusuwudeMacBook-Pro:bin yusuwu$ lala="hello ysw" yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw yusuwudeMacBook-Pro:bin yusuwu$ /bin/bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ echo $lala bash-3.2$ exit exit yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw
通过上面代码可知:
[1]:定义局部变量:变量名=变量值
[2]:变量名,等号和值之间不能有空格,如果在赋值表达式中加上了空格,bash shell 就会把值当成一个单独的命令.
[3]:如果要给变量赋给一个有空格的值,必须用引号来界定字符串的首尾.
[4]:局部变量无法在子shell中使用.
3:设置去全局变量
3.1:在设定全局环境变量的进程所创建的子进程中,该变量都是可见的.创建全局环境变量的方法是先创建一个局部环境变量,然后将它导出到全局环境中.
这个过程通过export命令来完成,变量名前面不需要加$.
yusuwudeMacBook-Pro:bin yusuwu$ echo $lala yusuwudeMacBook-Pro:bin yusuwu$ lala="hello ysw" yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw yusuwudeMacBook-Pro:bin yusuwu$ export lala yusuwudeMacBook-Pro:bin yusuwu$ bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ echo $lala hello ysw bash-3.2$ exit exit yusuwudeMacBook-Pro:bin yusuwu$ unset lala yusuwudeMacBook-Pro:bin yusuwu$ echo $lala yusuwudeMacBook-Pro:bin yusuwu$
3.2:子shell无法使用exprot命令来改变父shell中全局环境变量的值
yusuwudeMacBook-Pro:bin yusuwu$ echo $lala yusuwudeMacBook-Pro:bin yusuwu$ lala="hello ysw" yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw yusuwudeMacBook-Pro:bin yusuwu$ export lala yusuwudeMacBook-Pro:bin yusuwu$ bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ echo $lala hello ysw bash-3.2$ lala="hello yusuwu" bash-3.2$ echo $lala hello yusuwu bash-3.2$ export lala bash-3.2$ echo $lala hello yusuwu bash-3.2$ exit exit yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw yusuwudeMacBook-Pro:bin yusuwu$ bash The default interactive shell is now zsh. To update your account to use zsh, please run `chsh -s /bin/zsh`. For more details, please visit https://support.apple.com/kb/HT208050. bash-3.2$ echo $lala hello ysw bash-3.2$ exit exit yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw yusuwudeMacBook-Pro:bin yusuwu$ unset lala yusuwudeMacBook-Pro:bin yusuwu$ echo $lala yusuwudeMacBook-Pro:bin yusuwu$
3.3:删除环境变量 unset environmentVariable
yusuwudeMacBook-Pro:bin yusuwu$ echo $lala hello ysw yusuwudeMacBook-Pro:bin yusuwu$ unset lala yusuwudeMacBook-Pro:bin yusuwu$ echo $lala yusuwudeMacBook-Pro:bin yusuwu$
