Bash script programming variable one

Bash Variable type

Environment variables

Local variables (local variables)

Positional variables

Special variables

Local variables:

Varname=valoe: scope for the entire bash process

Local variables:

Local Varname=valoe: Scope is the current code snippet

Environment variables:

Similar to local variable: scope is the current shell process and its child processes

Export Varname=valoe

Positional variables:

$ =

Special variables:

$?: Execution status return value of previous command

Program execution, there are two types of possible return values:

1. Program execution Results

2. Program Status return code (0-255)

0: Indicates proper execution

1-255: Indicates error execution, 1,2,127 system reserved

Undo Variable:

Unset VARNAME

View variables in the current shell

Set

View environment variables in the current shell

Printenv

Env

Export

The script starts a child shell process when it executes

command-line-initiated scripts inherit the current shell's environment variables

Scripts that are automatically executed by the system do not inherit and need to be self-defined environment variables

Script: Command stack, according to the actual needs, combined with the command flow control mechanism to implement the source program

The first line of the script must define its execution shell example: #!/bin/bash

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Bash script programming variable one