Shell and bash variable types

The Shell is process-oriented

(Bash for example)

Variables are process variables, process ends, and variables disappear.

Bash Variable type:

Environment variables

Local variables (local variables):

Positional variables

Special variables

Local variables: Set Varname=value

scope for the entire bash process

Local variables:

local Varname=value scope is the current code snippet

environment variable: scope is the current shell process and its child processes

Export varname=VALUE

Or

Varname=value

Export VARNAME

Positional variables:

$

Special variables:

$? Save last command execution status return value

program execution, there may be two kinds of return values:

Status Return code: (0~255)

0: Correct execution

1-255: Various error executions, 1, 2, 127 system reserved

echo $? Look at the results

-------------------------------------------

/dev/null: Software devices, data black holes

-------------------------------------------

Undo Variable

Unset VARNAME

(The $VARNAME represents the action value, not the $ representation of the action variable)

View variables for the current shell

Set (including environment variables and local variables)

To view environment variables in the current shell:

Printenv

Env

Export

modifying variables

Ga=aaa

Modified: ga= $GA: Aa:ss separated by colons

Variable does not do arithmetic arithmetic (default is string save)

A=3

B=3

c= $A + $B

echo $C//3+3

Linux is just a no elf executable file

Script file First line

Shebang: Magic number (according to this selection shell execution)

#！ /bin/bash

If the script cannot execute:

1. Permissions

2. Environment variable (can write absolute path if no environment variable is added)

3. Or use the Interpreter directly (bash) to execute bash f.sh, if you want it to execute independently, you must have execute permissions.

This article from the "90 Design Studio" blog, reproduced please contact the author!

Shell and bash variable types