Linux-bash Environment variables

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Date: 2015.09.07

Linux_bash Environment variables

Bash explained

Bash can be a command language interpreter

/etc/profile.d/*.sh
~/.bash_profile
Function:
(1) Define environment variables, such as path, PS1
(2) run a command or script
BASHRC class: Provides configuration for non-interactive logon shell
/etc/bashrc
~/.bashrc

Function:
(1) Define command aliases;
(2) define local variables;

Variables: Memory space, variable name, changeable amount

Type:
Environment variables: scope current shell process and its child processes

Local variable: scope current shell process

Local variables: scoped only to a snippet of code in the current shell process (usually a function context)
Position variable: $ $, $
Special variables: $?
How variables are defined:
Bash built-in variables: can be called directly, built in a number of environment variables, such as Path
Custom variables:
Variable assignment: variable name = value
Bash Weak type:
When a variable stores data, it is written by default, and any variable can be directly referenced without being declared;
120:24bits
120:8bits
To define a local variable:

Defining Variables Name=value

Go to the next bash bash

View: Set

For details, see:

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Define Environment variables:
Define environment variables export name=value or use Declare-x name=value

See how many of the environment variables are used: env, printenv, export

See:

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Undo Variable:
unset name

See:

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Reference variable:
${name}, $name

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Reference symbols in bash:
': Strong reference, variable substitution does not occur

"": weak reference, variable substitution will occur

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": Command Reference

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Shell Logon Type:
Interactive login:
Login directly through the terminal;
User Switching implemented by su-l username command;
Non-interactive logon:
A command-line window opens under the graphical interface;
Execute the script;
Su Username;
Configuration file Action Order:
Interactive login:
/etc/profile--/etc/profile.d/*.sh--and ~/.bash_profile--~/.BASHRC--/ETC/BASHRC

Non-interactive logon:
~/.BASHRC--/ETC/BASHRC-/etc/profile.d/*.sh

The more the sequence

How does the new configuration of the Edit profile definition take effect?
(1) Re-login;
(2) Let the current shell process to re-read the specified configuration file;
Source/path/to/somefile
. /path/to/somefile
Note: Side effects

Problem:

1. Define aliases that are valid for all users?

Vim/etc/bashrc

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2. What if only the modification of the PATH environment variable takes effect for the root user?

Vim ~/.bash_profile

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Okay, here we are.

This article is from the "It-style" blog, make sure to keep this source http://huichengu.blog.51cto.com/2495968/1692566

Linux-bash Environment variables