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export
Set the export attribute for a shell variable or function.
overview
export [-fn] [name[=word]]...
export -p
The main purpose
- Define one or more variables and set export properties.
- Modify the value of one or more variables and set export properties.
- Removes the exported properties of one or more variables.
- Displays all variables that have exported properties.
- Adds an export attribute for one or more defined functions.
- Removes the export attribute of one or more functions.
- Shows all functions that have an exported attribute.
options
-f: points to a function.-n: Removes the export attribute of the variable.-p: Display all variables with export properties.-pf: Display all functions with export attributes.-nf: Removes the export attribute of the function.--: options after it are invalid.
parameter
name(Optional): Variable name or defined function name.value(Optional): The value of the variable.
return value
exportReturns true unless you provide an invalid option or invalid name.
example
# 显示全部拥有导出属性的变量。
# export -p
# export
# 显示全部拥有导出属性的函数。
# export -pf
# 首先删除要演示的变量名
# unset a b
# 定义变量的同时增加导出属性
export a b=3
# 当然也可以先定义后增加导出属性
b=3
export b
# 修改拥有导出属性的变量的值
export a=5 b=7
# 当然也可以直接赋值修改
a=5;b=7
# 删除变量的导出属性
export -n a b
# 首先删除要演示的函数名
unset func_1 func_2
# 创建函数
function func_1(){
echo '123'; }
function func_2(){
echo '890'; }
# 为已定义函数增加导出属性
export -f func_1 func_2
# 删除函数的导出属性
export -fn a b
# 添加环境变量（JAVA）到`~/.bashrc`
PATH=/usr/local/jdk1.7.0/bin:$PATH
# 添加当前位置到动态库环境变量
export LD_LIBRARY_PATH=$(pwd):${LD_LIBRARY_PATH}
wrong usage
- Add export attribute to undefined functions.
- Execute the remove export attribute operation on functions/variables that do not have an export attribute.
--Use options after .
Q&A
-
Q: What is the use of setting export properties on variables or functions?
- A: They will become environment variables, which can be accessed in the script, especially if the subprocess called in the script needs it. (reference link 4)
-
Q: If the script I wrote modifies the value of an existing environment variable, will it take effect in the current terminal when executed? Will it affect terminals opened before and after?
- A: Only
sourcescripts invoked via the method will take effect, you can checksourcethe command for more information; other methods are only executed in a subshell. The previous ones will not be affected, and the later ones will not be affected unless~/.bashrcthe script loaded when starting the terminal is modified. (reference link 1)
- A: Only
-
Q: I call
~/.bashrcthe functions and variables defined in the script file. Why can't these functions and variables be used when the script is invoked through sh in the newly opened terminal or the script that the current user has execution permission is run directly?- A: Please
~/.bashrcaddexporttheir statements in the file. See also the Knowledge Points paragraph.
- A: Please
-
Q: Can arrays and associative arrays also set export properties?
- A: Yes (if your bash supports them), but there are some problems (see link 2).
-
Q: Why do I display declare at the beginning when I view the export properties of variables or functions?
- A: Because
declarecan also set the export properties of variables or functions, seedeclarethe command for details.
- A: Because
Notice
This command is basha built-in command, please refer to command for related help information help.
knowledge points
The shell execution environment is mentioned in section 3.7.3 of info bash or bash online documentation , and the contents involving variables and functions are as follows:
- shell parameters that are set by variable assignment or with set or inherited from the shell’s parent in the environment
- shell functions defined during execution or inherited from the shell’s parent in the environment
So what does the parameter in the first sentence have to do with the variable? In the first paragraph of Section 3.4 it is mentioned:
A variable is a parameter denoted by a name.
Variables are named parameters.
Then the subshell does inherit the variable or function with the export attribute from the parent shell.
You can refer to the link: Differences in the way of executing scripts
reference link
- Discussion about bashrc profile file
- Discussion about export array
- export -pf Usage
- The difference between environment variables and shell variables
further reading
Generally speaking, when configuring the cross-compilation toolchain, you need to specify the path of the compilation tool, and you need to set the environment variable at this time. View existing environment variables:
[root@localhost ~]# export
declare -x G_BROKEN_FILENAMES="1"
declare -x HISTSIZE="1000"
declare -x HOME="/root"
declare -x hostname="localhost"
declare -x INPUTRC="/etc/inputrc"
declare -x LANG="zh_CN.UTF-8"
declare -x LESSOPEN="|/usr/bin/lesspipe.sh %s"
declare -x logname="root"
declare -x LS_COLORS="no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:bd=40;33;01:cd=40;33;01:or=01;05;37;41:mi=01;05;37;41:ex=01;32:*.cmd=01;32:*.exe=01;32:*.com=01;32:*.btm=01;32:*.bat=01;32:*.sh=01;32:*.csh=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.gz=01;31:*.bz2=01;31:*.bz=01;31:*.tz=01;31:*.rpm=01;31:*.cpio=01;31:*.jpg=01;35:*.gif=01;35:*.bmp=01;35:*.xbm=01;35:*.xpm=01;35:*.png=01;35:*.tif=01;35:"
declare -x mail="/var/spool/mail/root"
declare -x OLDPWD
declare -x PATH="/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"
declare -x pwd="/root"
declare -x SHELL="/bin/bash"
declare -x SHLVL="1"
declare -x SSH_CLIENT="192.168.2.111 2705 22"
declare -x SSH_CONNECTION="192.168.2.111 2705 192.168.2.2 22"
declare -x SSH_TTY="/dev/pts/0"
declare -x TERM="linux"
declare -x USER="root"
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