Shell Script Note 1

Finding mathematical expressions

VALUE=$[6/3]

value=$ ((6/3))

Let "value + = 1"

Defining local Variables

Local value

defining integers

Declare-i value

Command substitution

Value= ' Command '

value=$ (command)

System variables

$n, nth parameter

$#, number of parameters

$, current shell script name

$?, previous command exit status

$*, returned with "parameter 1 parameter 2"

[email protected], returned with "parameter 1" "Parameter 2"

$$, ID of this process

$!, previous process ID

$-, flag at a glance using the SET command

$PS 1

Clear variables

Unset ariable_name

Number of rows calculated: Wc-l

Sets the shell that executes the script, located in the first row of the #!:#!/bin/bash

echo output does not break line: echo-n

Turn off automatic printing of input characters: Stty-echo

Turn on auto-print input characters: stty Echo

Open command trace: set-x

Turn off command tracking: Set +x

Shell Script Note 1